{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_60212/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_60212","id":"gutenberg_60212","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/60212","summary":null,"tags":["Category: Philosophy & Ethics","Category: Psychiatry/Psychology","Category: Science - Biology","Mind and body","Psychophysiology"],"text":"Transcriber\u2019s Note\n\nIn PROBLEM I, CHAPTER III, Section 45 (originally page 38), chemical\nformulas represent the numbers of atoms in a molecule with patterns\nlike this: C_{114}. Throughout this eBook, pairs of underscores enclose\nitalicized text, Small-caps text appears as ALL-CAPS, and pairs of\nequals signs enclose boldface text.\n\n\n\n\nWorks by the same Author.\n\n\n  =PROBLEMS OF LIFE AND MIND. The Foundations of a Creed.= Two\n      Volumes. Octavo. Per volume, $3.00.\n\n      CONTENTS: The Method of Science and its Applications to\n      Metaphysics--The Rules of Philosophizing--Psychological\n      Principles--The Limitations of Knowledge--The Principles\n      of Certitude--From the Known to the Unknown--Matter and\n      Force--Force and Cause--The Absolute in the Correlations of\n      Feeling and Motion.\n\n  =THE STORY OF GOETHE\u2019S LIFE.= New Edition. One volume. 16mo. With\n      Portrait. $1.50.\n\n*.* _For sale by all Booksellers. Sent, post-paid, on receipt of price\nby the Publishers,_\n\n\nHOUGHTON, MIFFLIN & CO., BOSTON.\n\n\n\n\n  THE\n  PHYSICAL BASIS OF MIND.\n\n  With Illustrations.\n\n\n  _BEING THE SECOND SERIES_\n  OF\n  PROBLEMS OF LIFE AND MIND.\n\n  BY\n  GEORGE HENRY LEWES.\n\n  [Illustration: The Riverside Press.]\n\n  BOSTON AND NEW YORK:\n  HOUGHTON, MIFFLIN AND COMPANY.\n  The Riverside Press, Cambridge.\n  1891.\n\n\n\n\n  AUTHOR\u2019S EDITION.\n\n  _From Advance Sheets._\n\n\n  _The Riverside Press, Cambridge, Mass., U.\u00a0S.\u00a0A._\n  Printed by H.\u00a0O. Houghton & Company.\n\n\n\n\nPREFACE.\n\n\nThe title indicates that this volume is restricted to the group of\nmaterial conditions which constitute the organism in relation to the\nphysical world--a group which furnishes the data for one half of the\npsychologist\u2019s quest; the other half being furnished by historical and\nsocial conditions.\n\nThe Human Mind, so far as it is accessible to scientific inquiry, has\na twofold root, man being not only an animal organism but an unit in\nthe social organism; and hence the complete theory of its functions and\nfaculties must be sought in this twofold direction. This conception\n(which has been declared \u201cto amount to a revolution in Psychology\u201d),\nalthough slowly prepared by the growing conviction that Man could not\nbe isolated from Humanity, was first expounded in the opening volume of\nthese _Problems of Life and Mind_; at least, I am not aware that any\npredecessor had seen _how_ the specially human faculties of Intellect\nand Conscience were products of social factors co-operating with the\nanimal factors.\n\nIn considering the Physical Basis a large place must be assigned to\nthe mechanical and chemical relations which are involved in organic\nfunctions; yet we have to recognize that this procedure of Analysis is\nartificial and preparatory, that none of its results are final, none\nrepresent the synthetic reality of _vital_ facts. Hence one leading\nobject of the following pages has been everywhere to substitute\nthe biological point of view for the metaphysical and mechanical\npoints of view which too often obstruct research--the one finding its\nexpression in spiritualist theories, the other in materialist theories;\nboth disregarding the plain principle that the first requisite in a\ntheory of biological phenomena must be to view them in the light of\nbiological conditions: in other words, to fix our gaze upon what passes\nin the organism, and not on what may pass in the laboratory, where\nthe conditions are different. Analysis is a potent instrument, but\nis too often relied on in forgetfulness of what constitutes its real\naid, and thus leads to a disregard of all those conditions which it\nhas artificially set aside. We see this in the tendency of anatomists\nand physiologists to assign to _one_ element, in a complex cluster of\nco-operants, the significance which properly belongs to that cluster:\nas when the property of a tissue is placed exclusively in a single\nelement of that tissue, the function of an organ assigned to its chief\ntissue, and a function of the organism to a single organ.\n\nAnother object has been to furnish the reader uninstructed in\nphysiology with such a general outline of the structure and functions\nof the organism, and such details respecting the sentient mechanism,\nas may awaken an interest in the study, and enable him to understand\nthe application of Physiology to Psychology. If he comes upon details\nwhich can only interest specially educated students, or perhaps\nonly by them be really understood, he can pass over these details,\nfor their omission will not seriously affect the bearing of the\ngeneral principles. I have given the best I had to give; and must\nleave each reader to find in it whatever may interest him. The uses\nof books are first to stimulate inquiry by awakening an interest;\nsecondly, to clarify and classify the knowledge already gained from\ndirect contemplation of the phenomena. They are stimuli and aids to\nobservation and thought. They should never be allowed to see for us,\nnor to think for us.\n\nThe volume contains four essays. The first, on the _Nature of Life_,\ndeals with the speciality of organic phenomena, as distinguished\nfrom the inorganic. It sets forth the physiological principles which\nPsychology must incessantly invoke. In the course of the exposition I\nhave incorporated several passages from four articles on Mr. Darwin\u2019s\nhypotheses, contributed to the _Fortnightly Review_ during the year\n1868. I have also suggested a modification of the hypothesis of Natural\nSelection, by extending to the _tissues and organs_ that principle of\ncompetition which Mr. Darwin has so luminously applied to _organisms_.\nShould this generalization of the \u201cstruggle for existence\u201d be accepted,\nit will answer many of the hitherto unanswerable objections.\n\nThe second essay is on the _Nervous Mechanism_, setting forth what is\nknown and what is inferred respecting the structure and properties of\nthat all-important system. If the sceptical and revolutionary attitude,\nin presence of opinions currently held to be established truths,\nsurprises or pains the reader unprepared for such doubts, I can only\nask him to submit my statements to a similar scepticism, and confront\nthem with the ascertained evidence. After many years of laborious\ninvestigation and meditation, the conclusion has slowly forced\nitself upon me, that on this subject there is a \u201cfalse persuasion of\nknowledge\u201d very fatal in its influence, because unhesitatingly adopted\nas the ground of speculation both in Pathology and Psychology. This\npersuasion is sustained because few are aware how much of what passes\nfor observation is in reality sheer hypothesis. I have had to point out\nthe great extent to which Imaginary Anatomy has been unsuspectingly\naccepted; and hope to have done something towards raising a rational\nmisgiving in the student\u2019s mind respecting \u201cthe superstition of the\nnerve-cell\u201d--a superstition which I freely confess to have shared in\nfor many years.\n\nThe third essay treats of _Animal Automatism_. Here the constant\ninsistance on the biological point of view, while it causes a rejection\nof the mechanical theory, admits the fullest recognition of all the\nmechanical relations involved in animal movements, and thus endeavors\nto reconcile the contending schools. In this essay I have also\nattempted a psychological solution of that much-debated question--the\nrelation between Body and Mind. This solution explains why physical\nand mental phenomena must necessarily present to our apprehension\nsuch profoundly diverse characters; and shows that Materialism, in\nattempting to deduce the mental from the physical, puts into the\nconclusion what the very terms have excluded from the premises;\nwhereas, on the hypothesis of a physical process being only the\nobjective aspect of a mental process, the attempt to interpret the one\nby the other is as legitimate as the solution of a geometrical problem\nby algebra.\n\nIn the final essay the _Reflex Theory_ is discussed; and here once\nmore the biological point of view rectifies the error of an analysis\nwhich has led to the denial of Sensibility in reflex actions, because\nthat analysis has overlooked the necessary presence of the conditions\nwhich determine Sensibility. In these chapters are reproduced several\npassages from the _Physiology of Common Life_.\n\nAccording to my original intention, this volume was to have included an\nexposition of the part I conceive the brain to play in physiological\nand psychological processes, but that must be postponed until it can be\naccompanied by a survey of psychological processes which would render\nthe exposition more intelligible.\n\n  THE PRIORY, March, 1877.\n\n\n\n\nCONTENTS.\n\n\n  PROBLEM I. THE NATURE OF LIFE.\n\n\n  CHAPTER I.\n                                                                PAGE\n  THE PROBLEM STATED                                               3\n    (_The Position of Biology_)                                    4\n    (_Organisms_)                                                  8\n    (_Vital Force_)                                               14\n    (_Vital Force controlling Physical and Chemical Forces_)      16\n\n\n  CHAPTER II.\n\n  DEFINITIONS OF LIFE                                             24\n\n\n  CHAPTER III.\n\n  ORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE                   37\n    (_Organism and Medium_)                                       45\n    (_The Hypothesis of Germinal Matter_)                         57\n    (_Organisms and Machines_)                                    67\n\n\n  CHAPTER IV.\n\n  THE PROPERTIES AND FUNCTIONS                                    70\n    (_Does the Function determine the Organ?_)                    78\n\n\n  CHAPTER V.\n\n  EVOLUTION                                                       89\n    (_Natural Selection and Organic Affinity_)                   115\n    (_Recapitulation_)                                           152\n\n\n  PROBLEM II. THE NERVOUS MECHANISM.\n\n\n  CHAPTER I.\n\n  SURVEY OF THE SYSTEM,                                          157\n    (_The Early Forms of Nerve-Centres_),                        168\n    (_The Peripheral System_),                                   171\n    (_Ganglia and Centres_),                                     172\n\n\n  CHAPTER II.\n\n  THE FUNCTIONAL RELATIONS OF THE NERVOUS SYSTEM,                176\n\n\n  CHAPTER III.\n\n  NEURILITY,                                                     189\n    (_Origins of Nerve-Force_),                                  201\n    (_The Hypothesis of Specific Energies_),                     207\n\n\n  CHAPTER IV.\n\n  SENSIBILITY,                                                   211\n\n\n  CHAPTER V.\n\n  ACTION WITHOUT NERVE-CENTRES,                                  227\n\n\n  CHAPTER VI.\n\n  WHAT IS TAUGHT BY EMBRYOLOGY?,                                 237\n\n\n  CHAPTER VII.\n\n  THE ELEMENTARY STRUCTURE OF THE NERVOUS SYSTEM,                251\n    (_Difficulties of the Investigation_),                       252\n    (_The Nerve-Cell_),                                          258\n    (_The Nerves_),                                              270\n    (_The Neuroglia_),                                           273\n    (_The Relations of the Organites_),                          278\n    (_Recapitulation_),                                          299\n\n  CHAPTER VIII.\n\n  THE LAWS OF NERVOUS ACTIVITY                                   310\n    (_The Energy of Neurility_)                                  311\n    (_The Propagation of Excitation_)                            314\n    (_Stimuli_)                                                  321\n    (_Stimulation_)                                              324\n    (_The Law of Discharge_)                                     326\n    (_The Law of Arrest_)                                        333\n    (_The Hypothesis of Inhibitory Centres_)                     336\n    (_Anatomical Interpretations of the Laws_)                   339\n\n\n  PROBLEM III. ANIMAL AUTOMATISM.\n\n\n  CHAPTER I.\n\n  THE COURSE OF MODERN THOUGHT                                   345\n\n\n  CHAPTER II.\n\n  THE VITAL MECHANISM                                            363\n\n\n  CHAPTER III.\n\n  THE RELATION OF BODY AND MIND                                  376\n\n\n  CHAPTER IV.\n\n  CONSCIOUSNESS AND UNCONSCIOUSNESS                              399\n\n\n  CHAPTER V.\n\n  VOLUNTARY AND INVOLUNTARY ACTIONS                              415\n\n\n  CHAPTER VI.\n\n  THE PROBLEM STATED                                             431\n\n\n  CHAPTER VII.\n\n  IS FEELING AN AGENT?                                           440\n\n\n  PROBLEM IV. THE REFLEX THEORY.\n\n\n  CHAPTER I.\n\n  THE PROBLEM STATED                                             467\n\n\n  CHAPTER II.\n\n  DEDUCTIONS FROM GENERAL LAWS                                   490\n\n\n  CHAPTER III.\n\n  INDUCTIONS FROM PARTICULAR OBSERVATIONS                        509\n    (_Cerebral Reflexes_)                                        511\n    (_Discrimination_)                                           520\n    (_Memory_)                                                   522\n    (_Instinct_)                                                 522\n    (_The Acquisition of Instinct_)                              536\n    (_Acquisition_)                                              546\n\n\n  CHAPTER IV.\n\n  NEGATIVE INDUCTIONS                                            550\n\n\n\n\nPROBLEM I.\n\nTHE NATURE OF LIFE.\n\n    \u201cLa Physiologie a pour but d\u2019exposer les ph\u00e9nom\u00e8nes de la vie\n    humaine et les conditions d\u2019o\u00f9 ils d\u00e9pendant. Pour y arriver\n    d\u2019une mani\u00e8re s\u00fbre, il faut n\u00e9cessairement avant tout d\u00e9terminer\n    quels sont les ph\u00e9nom\u00e8nes qu\u2019on d\u00e9signe sous le nom de vie en\n    g\u00e9n\u00e9ral. C\u2019est pourquoi la premi\u00e8re chose \u00e0 faire est d\u2019\u00e9tudier\n    les propri\u00e9t\u00e9s g\u00e9n\u00e9rales du corps qu\u2019on appelle organiques ou\n    vivans.\u201d--TIEDEMANN, _Trait\u00e9 de Physiologie de l\u2019Homme_, I. 2.\n\n    \u201cSome weak and inexperienced persons vainly seek by dialectics and\n    far-fetched arguments either to upset or establish things that are\n    only to be founded on anatomical demonstration and believed on the\n    evidence of the senses. He who truly desires to be informed of the\n    question in hand must be held bound either to look for himself, or\n    to take on trust the conclusions to which they who have looked have\n    come.\u201d--HARVEY, _Second Dissertation to Riolan_.\n\n\n\n\nTHE NATURE OF LIFE.\n\n\n\n\nCHAPTER I.\n\nTHE PROBLEM STATED.\n\n\n1. Although for convenience we use the terms Life and Mind as\nrepresenting distinct orders of phenomena, the one objective and the\nother subjective, and although for centuries they have designated\ndistinct entities, or forces having different substrata, we may now\nconsider it sufficiently acknowledged among scientific thinkers that\nevery problem of Mind is necessarily a problem of Life, referring to\none special group of vital activities. It is enough that Mind is never\nmanifested except in a living organism to make us seek in an analysis\nof organic phenomena for the material conditions of every mental fact.\nMental phenomena when observed in others, although interpretable by our\nconsciousness of what is passing in ourselves, can only be objective\nphenomena of the vital organism.\n\n2. On this ground, if on this alone, an acquaintance with the\ngeneral principles of structure and function is indispensable to\nthe psychologist; although only of late years has this been fully\nrecognized, so that men profoundly ignorant of the organism have had\nno hesitation in theorizing on its highest functions. In saying that\nsuch knowledge is indispensable, I do not mean that in the absence\nof such knowledge a man is debarred from understanding much of the\nresults reached by investigators, nor that he may not himself make\nuseful observations and classifications of psychological facts. It is\npossible to read books on Natural History with intelligence and profit,\nand even to make good observations, without a scientific groundwork of\nbiological instruction; and it is possible to arrive at empirical facts\nof hygiene and medical treatment without any physiological instruction.\nBut in all three cases the absence of a scientific basis will render\nthe knowledge fragmentary and incomplete; and this ought to deter\nevery one from offering an opinion on debatable questions which pass\nbeyond the limit of subjective observations. The psychologist who has\nnot prepared himself by a study of the organism has no more right to\nbe heard on the genesis of the psychical states, or of the relations\nbetween body and mind, than one of the laity has a right to be heard on\na question of medical treatment.\n\n\nTHE POSITION OF BIOLOGY.\n\n3. Science is the systematic classification of Experience. It\npostulates unity of Existence with great varieties in the Modes of\nExistence; assuming that there is one Matter everywhere the same,\nunder great diversities in the complications of its elements. The\ndistinction of Modes is not less indispensable than the identification\nof the elements. These Modes range themselves under three supreme\nheads: Force, Life, Mind. Under the first, range the general properties\nexhibited by _all_ substances; under the second, the general properties\nexhibited by _organized_ substances; under the third, the general\nproperties exhibited by organized _animal_ substances. The first\nclass is subdivided into _Physics_, celestial and terrestrial, and\n_Chemistry_. Physics treats of substances which move as masses,\nor which vibrate and rotate as molecules, without undergoing any\nappreciable change of structural integrity; they show changes of\n_position_ and _state_, without corresponding changes in their\nelements. Chemistry treats of substances which undergo molecular\nchanges of composition _destructive_ of their integrity. Thus the blow\nwhich simply moves one body, or makes it vibrate, explodes another. The\nfriction which alters the temperature and electrical state of a bit of\nglass, ignites a bit of phosphorus, and so destroys its integrity of\nstructure, converting phosphorus into phosphoric acid.\n\n4. The second class, while exhibiting both physical and chemical\nproperties, is markedly distinguished by the addition of properties\ncalled vital. Their peculiarity consists in this: they undergo\nmolecular changes of composition and decomposition which are\nsimultaneous, and _by this simultaneity preserve their integrity of\nstructure_. They change their state, and their elements, yet preserve\ntheir unity, and even when differentiating continue specific. Unlike\nall other bodies, the organized are born, grow, develop, and decay,\nthrough a prescribed series of graduated evolutions, each stage being\nthe indispensable condition of its successor, no stage ever appearing\nexcept in its serial order.\n\n5. The third class, while exhibiting all the characteristics of the\ntwo preceding classes, is specialized by the addition of a totally\nnew property, called Sensibility, which subjectively is Feeling. Here\norganized substance has become animal substance, and Vegetality has\nbeen developed into Animality by the addition of new factors,--new\ncomplexities of the elementary forces. Many, if not most, philosophers\npostulate an entirely new Existence, and not simply a new Mode, to\naccount for the manifestations of Mind; they refuse to acknowledge\nit to be a vital manifestation, they demand that to Life be added a\nseparate substratum, the Soul. This is not a point to be discussed\nhere. We may be content with the assertion that however great the\nphenomenal difference between Humanity and Animality (a difference we\nshall hereafter see to be the expression of a new factor, namely, the\nsocial factor), nevertheless the distinctive attribute of Sensibility,\nout of which rise Emotion and Cognition, marks the inseparable\n_kinship_ of mental with vital phenomena.\n\nThus all the various Modes of Existence may, at least in their\nobjective aspect, be ranged under the two divisions of Inorganic and\nOrganic,--Non-living and Living,--and these are respectively the\nobjects of the cosmological and the biological sciences.\n\n6. The various sciences in their serial development develop the\nwhole art of Method. Mathematics develops abstraction, deduction,\nand definition; Astronomy abstraction, deduction, and observation;\nPhysics adds experiment; Chemistry adds nomenclature; Biology adds\nclassification, and for the first time brings into prominence the\nimportant notion of _conditions of existence_, and the variation\nof phenomena under varying conditions: so that the relation of the\norganism to its medium is one never to be left out of sight. In\nBiology also clearly emerges for the first time what I regard as the\ntrue notion of causality, namely, the _procession_ of causes,--the\ncombination of factors in the product, and not an _ab extra_\ndetermination of the product. In Vitality and Sensibility we are made\naware that the causes are _in_ and not _outside_ the organism; that\nthe organic effect is the organic cause in operation; that there is\nautonomy but no autocracy; the effect issues as a resultant of the\nco-operating conditions. In Sociology, finally, we see brought into\nprominence the _historical conditions of existence_. From the due\nappreciation of the conditions of existence, material and historical,\nwe seize the true significance of the principle of Relativity.\n\n7. Having thus indicated the series of the abstract sciences we have\nnow to consider more closely the character of Biology. The term was\nproposed independently yet simultaneously in Germany and France, in\nthe year 1802, by Treviranus and Lamarck, to express \u201cthe study of the\nforms and phenomena of Life, the conditions and laws by which these\nexist, and the causes which produce them.\u201d Yet only of late years has\nit gained general acceptance in France and England. The term Cosmology,\nfor what are usually called the Physical Sciences, has not yet come\ninto general use, although its appropriateness must eventually secure\nits recognition.\n\nBiology,--the abstract science of Life,--embracing the whole organic\nworld, includes Vegetality, Animality, and Humanity; the biological\nsciences are Phytology, Zo\u00f6logy, and Anthropology. Each of the\nsciences has its cardinal divisions, statical and dynamical, namely,\nMorphology--the science of form,--and Physiology--the science of\nfunction.\n\nMorphology embraces--1\u00b0, _Anatomy_, i.\u00a0e. the description of the parts\nthen and there present in the organism; and these parts, or organs, are\nfurther described by the enumeration of their constituent tissues and\nelements; and of these again the proximate principles, so far as they\ncan be isolated without chemical decomposition. 2\u00b0, _Organogeny_, i.\u00a0e.\nthe history of the evolution of organs and tissues.\n\nPhysiology embraces the properties and functions of the tissues and\norgans--the primary conditions of Growth and Development out of\nwhich rise the higher functions bringing the organism into active\nrelation with the surrounding medium. The first group of properties\nand functions are called those of vegetal, or organic life; the second\nthose of animal, or relative life.\n\n\nORGANISMS.\n\n8. It will be needful to fix with precision the terms, Organism, Life,\nProperty, and Function.\n\nAn organism, although usually signifying a more or less complex unity\nof organs, because the structures which first attracted scientific\nattention were all thus markedly distinguished from inorganic\nbodies, has by the gradual extensions of research been necessarily\ngeneralized, till it now stands for any organized substance capable of\nindependent vitality: in other words, any substance having the specific\ncombination of elements which manifests the serial phenomena of growth,\ndevelopment, and decay. There are organisms that have no differentiated\norgans. Thus a microscopic formless lump of semifluid jelly-like\nsubstance (Protoplasm) is called an organism, because it feeds itself,\nand reproduces itself. There are advantages and disadvantages in such\nextensions of terms. These are notable in the parallel extension of\nthe term Life, which originally expressing only the complex activities\nof complex organisms, has come to express the simplest activities of\nprotoplasm. Thus a Monad is an organism; a Cell is an organism; a Plant\nis an organism; a Man is an organism. And each of these organisms is\nsaid to have its Life, because\n\n    \u201cThrough all the mighty commonwealth of things\n     Up from the creeping worm to sovereign man\u201d[1]\n\nthere is one fundamental group of conditions, one organized substance,\none vitality.\n\nObviously this unity is an abstraction. In reality, the life manifested\nin the Man is _not_ the life manifested in the Monad: he has Functions\nand Faculties which the Monad has no trace of; and if the two organisms\nhave certain vital characteristics in common, this unity is only\nrecognized in an _ideal construction_ which lets drop all concrete\ndifferences. The Life is different when the organism is different.\nHence any definition of Life would be manifestly insufficient which\nwhile it expressed the activities of the Monad left unexpressed the\nconspicuous and important activities of higher organisms. A sundial\nand a repeater will each record the successive positions of the sun\nin the heavens; but although both are instruments for marking time,\nthe sundial will not do the work of the repeater; the complexity and\ndelicacy of the watch mechanism are necessary for its more varied and\ndelicate uses. A semifluid bit of protoplasm will feed itself; but it\nwill not feed and sustain a complex animal; nor will it feel and think.\n\n9. Neglect of this point has caused frequent confusion in the attempts\nto give satisfactory definitions. Biologists ought to have been warned\nby the fact that some of the most widely accepted definitions exclude\nthe most conspicuous phenomena of Life, and are only applicable to the\nvegetable world, or to the vegetal processes in the animal world. A\ndefinition, however abstract, should not exclude essential characters.\nThe general consent of mankind has made Life synonymous with Mode of\nExistence. By the life of an animal is meant the existence of that\nanimal; when dead the _animal_ no longer exists; the substances of\nwhich the organism was composed exist, but under another mode; their\nconnexus is altered, and the organism vanishes in the alteration.\nIt is a serious mistake to call the corpse an organism; for that\n_special_ combination which constituted the organism is not present in\nthe corpse. This misconception misleads some speculative minds into\nassigning life to the universe. The universe assuredly exists, but it\ndoes not live; its existence can only be identified with life, such as\nwe observe in organisms, by a complete obliteration of the speciality\nwhich the term Life is meant to designate. Yet many have not only\npleased themselves with such a conception, but have conceived the\nuniverse to be an organism fashioned, directed, and sustained by a soul\nlike that of man--the _anima mundi_. This is to violate all scientific\ncanons. The life of a plant-organism is not the same as the life of an\nanimal-organism; the life of an animal-organism is not the same as the\nlife of a human-organism; nor can the life of a human-organism be the\nsame as the life of the world-organism. The unity of Existences does\nnot obliterate the variety of Modes; yet it is the speciality of each\nMode which Science investigates; to some of these Modes the term Life\nis consistently applied, to others not; and if we merge them all in a\ncommon term, we must then invent a new term to designate the Modes now\nincluded under Life.\n\n10. In resisting this unwarrantable extension of the term I am not\nonly pointing to a speculative error, but also to a serious biological\nerror common in both spiritualist and materialist schools, namely\nthat of assigning Life to other than organic agencies. Instead of\nrecognizing the speciality of this Mode of Existence as dependent on\na speciality of the organic conditions, the spiritualist assigns Life\nto some extra-organic Vital Principle, the materialist assigns it to\nsome inorganic agent--physical or chemical. Waiving for the present all\ndiscussion of Vitalism, let us consider in what sense we must separate\norganic from all inorganic phenomena.\n\n11. There is a distinction between inorganic and organic which may\nfitly be called radical: it lies at the root of the phenomena, and must\nbe accepted as an ultimate fact, although the synthesis on which it\ndepends is analytically reducible to a complication of more primitive\nconditions. It has been already indicated in \u00a7 5. All organisms above\nthe very simplest are syntheses Of three terms: Structure, Aliment,\nand Instrument. Crystals, like all other anorganisms have structure,\nand in a certain sense they may be said to grow (_Mineralia crescunt_),\nthough the growth is by _increase_ and not by _modification_:[2]\nthe motherlye, which is the food of the crystal, is never brought\nto the crystal, nor prepared for it, by any instrumental agency of\nthe crystal. Organisms are exclusively instrumental; the organ is an\ninstrument. The structural integrity of an organism is thus preserved\nthrough an alimentation which is effected through special instruments.\nNothing like this is visible in anorganisms.\n\nThe increase of a crystal is further distinguishable from the growth\nof an organism, in the fact Of its being simple accretion without\ndevelopment; and the structure of the crystal is distinguishable from\nthat of an organism in the fact that its integrity is preserved by\nthe _exclusion_ of all molecular change, and not by the simultaneous\nchanges of molecular decomposition and recomposition. Inorganic\nsubstances are sometimes as unstable as organic, sometimes even more\nunstable; but their instability is the source of their structural\ndestruction--they change into other species; whereas the instability\nof _organized_ substances (_not_ of organic) is the source of their\nstructural integrity: the tissue is renovated, and its renovation is a\nconsequence of its waste.\n\n12. But while the distinction is thus radical, when we view the\norganism from the _real_--that is, from the synthetic point of view--we\nmust also urge the validity of the analytical point of view, which\nseizes on the conditions here complicated in a special group, and\ndeclares these conditions to be severally recognizable equally in\nanorganisms and in organisms. All the fundamental properties of Matter\nare recognizable in organized Matter. The elementary substances and\nforces familiar to physicists and chemists are the materials of the\nbiologist; nor has there been found a single organic substance, however\nspecial, that is not reducible to inorganic elements. We see, then,\nthat organized Matter is only a special combination of that which in\n_other_ combinations presents chemical and physical phenomena; and we\nare prepared to find Chemistry and Physics indispensable aids in our\nanalysis of organic phenomena. Aids, but only aids; indispensable, but\ninsufficient.\n\n13. There is therefore an ambiguity in the common statement that\norganized matter is not _ordinary_ matter. Indisputable in one sense,\nthis is eminently disputable when it is interpreted as evidence of\na peculiar Vital Force \u201cwholly unallied with the primary energy of\nMotion.\u201d If by \u201cordinary matter\u201d be meant earths, crystals, gases,\nvapors, then assuredly organized matter is not ordinary. \u201cBetween the\n_living_ state of matter and its _non-living_ state,\u201d says Dr. Beale,\n\u201cthere is an absolute and irreconcilable difference; so far from our\nbeing able to demonstrate that the non-living passes by gradations\ninto or gradually assumes the scale or condition of the _living_, the\ntransition is sudden and abrupt, and matter already in the living\nstate may pass into the non-living condition in the same sudden and\ncomplete manner.\u201d[3] The ambiguity here is sensible in the parallel\ncase of the difference between crystallizable and coagulable matter, or\nbetween one crystal and another. If we can decompose the organic into\nthe inorganic, this shows that the elements of the one are elements\nof the other; and if we are not yet able to recompose the inorganic\nelements into organic matter (not at least in its more complex forms),\nmay this not be due to the fact that we are ignorant of the proximate\nsynthesis, ignorant of the precise way in which the elements are\ncombined? I may have every individual part of a machine before me, but\nunless I know the proper position of each, I cannot with the parts\nreconstruct the machine. Indeed the very common argument on which so\nmuch stress is laid in favor of some mysterious Principle as the source\nof organic phenomena, namely, that human skill is hopelessly baffled in\nthe attempt to make organic substances, still more a living cell, is\nfutile. Men can make machines, it is said, but not organisms, _ergo_\norganisms must have a spiritual origin. But the fact is that no man can\nmake a machine, _unless_ he take advantage of the immense traditions of\nour race, and apply the skill of millions who have worked and thought\nbefore him, slowly and tentatively discovering the necessary means\nof mechanical effect. The greatest thinker, or the deepest scholar,\nwho did not place himself in the line of the tradition, and learn the\nprinciples of mechanism, and the properties of the materials, would be\nas incapable of making a watch, as the physiologist now is of making\na cell. But the skill of man has already succeeded in making many\norganic substances, and will perhaps eventually succeed in making a\ncell, certainly will, if ever the special synthesis which binds the\nelements together should be discovered. Not that such a discovery would\nalter the position of Biology in relation to Chemistry. The making of\nalbumen, nay, the construction of an organism in the laboratory, would\nnot in the least affect the foundation of Biology, would not obliterate\nthe radical difference between organisms and anorganisms. It is the\nspeciality of organic phenomena which gives them a special place,\nalthough the speciality may only be due to a complication of general\nagencies.\n\n\nVITAL FORCE.\n\n14. A similar ambiguity to that of the phrase \u201cordinary matter\u201d lies\nin the equally common phrase \u201cVital Force,\u201d which is used to designate\na special group of agencies, and is then made to designate an agent\nwhich has no kinship with the general group; that is to say, instead of\nbeing employed in its real signification--that which alone represents\nour knowledge--as the abstract statical expression of the complex\nconditions necessary to the manifestation of vital phenomena, or as\nthe abstract dynamical expression of the phenomena themselves, it\nis employed as an expression of their unknown Cause, which, because\nunknown, is dissociated from the known conditions, and erected into\na mysterious Principle, having no kinship with Matter. In the first\nsense the term is a shorthand symbol of what is known and inferred.\nThe known conditions are the relations of an organism and its medium,\nthe organism being the union of various substances all of which have\ntheir peculiar properties when isolated; properties that disappear\nin the union, and are replaced by others, which result from the\ncombination--as the properties of chlorine and sodium all disappear in\nthe sea-salt which results from their union; or as the properties of\noxygen and the properties of hydrogen disappear and are replaced by the\nproperties of water. When therefore Vital Force is said to be exalted\nor depressed, the phrase has rational interpretation in the alteration\nwhich has taken place in one or more of the conditions, internal and\nexternal: a change in the tissues, the plasma, or the environment,\nexalts or depresses the energy of the vital manifestations; and to\nsuppose that this is effected through the agency of some extra-organic\nPrinciple is a purely gratuitous fiction.\n\n15. That we are ignorant of one or more of the indispensable conditions\nsymbolized in the abstract term Vitality or Vital Force, is no reason\nfor quitting the secure though difficult path of Observation, and\nrushing into the facile but delusive path of Fiction, which proposes\nmetempirical Agents (in the shape of Vital and Psychical Principles)\nto solve the problems of Life and Mind. We may employ the term Vital\nForce to label our observations, together with all that still remains\nunobserved; and we are bound to recognize the line which separates\nobservation from inference, what is proved from what is inferred;\nbut while marking the limits of the known, we are not to displace\nthe known in favor of the unknown. It is said that because of our\nignorance we must assume these causes of Life and Mind to be _unallied_\nwith known material causes, and belonging to a different order of\nexistences. This is to convert ignorance into a proof; and not only\nso, but to allow what we do not know to displace what we do know. The\norganicist is ready to admit that much has still to be discovered; the\nvitalist, taking his stand upon this unknown, denies that what has been\ndiscovered is really important, and declares that the real agent is\nwholly unallied to it. How _can_ he know this?\n\nHe does not know it; he assumes it; and the chief evidence he adduces\nis that the ordinary laws of inorganic matter are incapable of\nexplaining the phenomena of organized matter; and that physical and\nchemical forces are controlled by vital force. I accept both these\npositions, stripping them, however, of their ambiguities. The laws of\nordinary matter are clearly incompetent in the case of matter which is\nnot ordinary, but _specialized_ in organisms; and when we come to treat\nof Materialism we shall see how unscientific have been the hypotheses\nwhich disregard the distinction. The question of control is too\ninteresting and important to be passed over here.\n\n\nVITAL FORCE CONTROLLING PHYSICAL AND CHEMICAL FORCES.\n\n16. The facts relied on by the vitalists are facts which every\norganicist will emphasize, though he will interpret them differently.\nWhen, for example, it is said that \u201cLife resists the effect of\nmechanical friction,\u201d and the proof adduced is the fact that the\nfriction which will thin and wear away a dead body is actually the\ncause of the thickening of a living--the skin of a laborer\u2019s hand\nbeing thickened by his labor; the explanation is not that Life, an\nextra-organic agent, \u201cresists mechanical friction\u201d--for the mechanical\neffect is _not_ resisted (the skin is rubbed off the rower\u2019s hand\nsooner than the wood is rubbed off the oar)--but that Life, i.\u00a0e.\norganic activity repairs the waste of tissue.\n\n17. Again, although many of the physical and chemical processes which\ninvariably take place under the influences to which the substances\nare subjected out of the organism, will not take place at all, or\nwill take place in different degrees, when the substances are in the\norganism, this is important as an argument against the notion of vital\n_phenomena_ being deducible from physical and chemical _laws_, but is\nvalueless as evidence in favor of an extra-organic agent. Let us glance\nat one or two striking examples.\n\n18. No experimental inquirer can have failed to observe the often\ncontradictory results which seemingly unimportant variations in the\nconditions bring about; no one can have failed to observe what are\ncalled chemical affinities wholly frustrated by vital conditions. Even\nthe ordinary laws of Diffusion are not always followed in the organism.\nThe Am\u0153ba, though semifluid, resists diffusion when alive; but when it\ndies it swells and bursts by osmosis. The exchange of gases does not\ntake place in the tissues, precisely as in our retorts. The _living_\nmuscle respires, that is, takes up oxygen and gives out carbonic\nacid, not on the principle of simple diffusion, but by two separable\nphysiological processes. The carbonic acid is given out, even when\nthere is no oxygen whatever present in the atmosphere, and its place\nmay then be supplied by hydrogen; and this physiological process is so\ndifferent from the physical process which goes on in the dead muscle\n(the result of putrefaction), that it has been proved by Ranke to go\non when the temperature is so low that all putrefaction is arrested.\nThe same experimenter finds[4] that whereas living nerve will take up,\nby imbibition, 10 per cent of potash salts, it will not take up 1 per\ncent of soda salts, presented in equal concentration; and he points\nto the general fact that the absorption of inorganic substances does\n_not_ take place according to the simple laws of diffusion, but that\nliving tissues have special laws, the nerve, for instance, having\na greater affinity for neutral potash salts than for neutral soda\nsalts. Let me add, by way of anticipating the probable argument that\nmay urge this in favor of Vital Principle which is lightly credited\nwith the prescience of final causes, that so far from this \u201celective\naffinity\u201d of the tissues being intelligent and always favorable,\nRanke\u2019s experiments unequivocally show that it is more active towards\ndestructive, poisonous substances, than towards the reparative,\nalimentary substances; which is indeed consistent with the familiar\nexperience that poisons are more readily absorbed than foods, when both\nare brought to the tissues. Thus it is well known that of all the salts\nthe sulphate of copper is that which plants most readily absorb--and\nit kills them. The special affinities disappear as the vitality\ndisappears, and dying plants absorb all salts equally.\n\n19. The more the organism is studied, the more evident it will become\nthat the simple laws of diffusion, as presented in anorganisms rarely\nif ever take effect in tissues; in other words, what is called\nImbibition in Physics is the somewhat different process of Absorption\nin Physiology.[5] The difference is notable in this capital fact, that\nwhereas the physical diffusion of liquids and gases is determined\nby differences of density, the physiological absorption of liquids\nand gases is determined by the molecular organization of the tissue,\nwhich is perfectly indifferent to, and resists the entrance of, all\nsubstances incapable of entering into organic combination, either as\naliment or poison. A curious example of the indifference of organized\nsubstances to some external influences and their reaction upon others,\nis the impossibility of provoking ciliary movement in an epithelial\ncell, during repose, by any electrical, mechanical, or chemical stimuli\nexcept potash and soda. Virchow discovered that a minute quantity of\neither of these, added to the water in which the cell floated, at once\ncalled forth the ciliary movements.\n\n20. The true meaning of the resistance of Vitality to ordinary chemical\naffinity is, that the conditions involved in the phenomena of Vitality\nare not the conditions involved in the phenomena of Chemistry; in other\nwords, that in the living organism the substances are placed under\nconditions different from those in which we observe these substances\nwhen their chemical affinities are displayed in anorganisms. But we\nneed not go beyond the laboratory to see abundant examples of this\nso-called resistance to chemical affinity, when the conditions are\naltered. The decomposition of carbonates by tartaric acid is a chemical\nprocess which is wholly resisted if alcohol instead of water be the\nsolvent employed. The union of sulphur with lead is said to be due\nto the affinity of the one for the other; but no one supposes this\naffinity to be irrespective of conditions, or that the union will take\nplace when any one of these conditions is absent. If we fuse a compound\nof lead and iron in a crucible containing sulphur, we find it is the\niron, and not the lead, which unites with the sulphur; yet we do not\nconclude that there is a Crucible Principle which frustrates chemical\naffinity and resists the union of sulphur and lead; we simply conclude\nthat the presence of the iron is a condition which prevents the\ncombination of the sulphur with the lead: not until all the iron has\ntaken up its definite proportion of sulphur will the affinity of the\nlead come into play. This is but another illustration of the law that\n_effects are processions of their causes_, summations of the conditions\nof their existence. If the fire burns no hole in the teakettle so long\nas there is water to conduct the heat away, this is not due to any\nprinciple more mysterious than the presence of a readily conducting\nwater.[6]\n\n21. In accordance with the law of Causation just mentioned, which\nhas been expounded in detail in our First Series (Vol. II. p. 335),\nthe special combinations of Matter in organisms must present special\nphenomena. Therefore since the province of Biology is that of\nexplaining organic phenomena by means of their organic conditions,\nit must be radically distinguished from the provinces of Physics and\nChemistry, which treat not of organized but of inorganic matter. It\nis idle, it is worse, for it is misleading, to personify the organic\nconditions, known and inferred, in a Vital Principle; idle, because we\nmight with equal propriety personify the conditions of crystallization\nin a Crystal Principle; misleading, because the artifice is quickly\ndropped out of sight, and the abstract term then becomes accepted as\nan entity, supposed to create or rule the phenomena it was invented to\nexpress.\n\n22. Inquirers are but too apt to misconceive the value of Analysis,\nwhich is an artifice of Method indispensable to research, though\nneeding the complementary rectification by Synthesis before a real\nexplanation can be reached. Analysis decomposes the actual fact into\nideal factors, separates the group into its components, and considers\neach of these, not as it exists in the group, in the reality, but as\nit exists when theoretically detached from the others. The oxygen\nand hydrogen into which water is decomposed did not exist as these\ngases in the water; the albumen and phosphate we extract from a nerve\ndid not exist _as_ isolated albumen and phosphate in the nerve, they\nwere molecularly combined. In like manner the physical and chemical\nprocesses which may analytically be inferred in vital processes do\nnot really take place in the same way as out of the organism. The\nreal process is always a vital process, and must be explained by the\nsynthesis of all the co-operant conditions. The laws of Physics and\nChemistry formulate abstract expressions of phenomena, wherever and\nwhenever these appear, without reference to the _modes of production_;\nand in _this_ sense the movement of a limb is no less a case of\nDynamics than the movement of a pulley--the decomposition of a tissue\nis a case of Chemistry no less than the decomposition of a carbonate;\nthe electromotor phenomena observed in muscle are as purely physical\nas those observed in a telegraph. But when a biologist has to explain\nthe movements of the limbs, or the decompositions of tissues, he has\nto deal with the phenomena and their modes of production, he has\na particular group before him, and must leave out nothing that is\ncharacteristic of it. The movements of the pulley do not depend on\nContractility and Sensibility, which in turn depend on Nutrition. The\ndecomposition of the carbonate does not depend on conditions resembling\nthose of a living tissue. Vaucanson\u2019s duck was surprisingly like a\nliving duck in many of its movements; but in none of its actions was\nthere any real similarity to the actions of a bird, because the machine\nwas unlike an organism in action. The antithesis of mechanism and\norganism will be treated of in \u00a7 78.\n\n23. We conclude, then, that defining physical phenomena as the\nmovements which take place _without_ change of structure, and chemical\nphenomena as the movements _with_ change of structure, although\nboth classes may be said to take place in the organism, and to be\nthe primary conditions on which organic phenomena depend, they do\nnot embrace the whole of the conditions, nor are the sciences which\nformulate them capable of formulating either the special phenomena\ncharacteristic of organisms or their special modes of production. The\nbiologist will employ chemical and physical analysis as an essential\npart of his method; but he will always rectify what is artificial in\nthis procedure, by subordinating the laws of Physics and Chemistry\nto the laws of Biology revealed in the synthetic observation of\nthe organism as a whole. The rectification, here insisted on, will\nbe recognized as peculiarly urgent in Psychology, which has greatly\nsuffered from the misdirection of Analysis.\n\n24. No one will misunderstand this specialization of Biology to mean\na separation of Life from the series of objective phenomena, and\nthe introduction of a new entity; the specialization points to a\nMode of Existence. All classifications are artifices, but they have\ntheir objective grounds; the ground of difference on which Biology\nis separated from Chemistry and Physics, though all three may be\nmerged in a common identity, is such as to justify the term radical.\nA vital process is no more to be considered physico-chemical, because\nphysico-chemical conditions are presupposed in it, than a feeling is\nto be considered a nutritive process, because Nutrition is presupposed\nin all Feeling. Organic substances have been made by chemists, and\ninorganic \u201ccells\u201d have also been made; but these substances were not\norganized, these \u201ccells\u201d would not live. The germ-cell is the workshop\nof generation, the secreting-cell the workshop of secretion, the\nmuscle-cell the workshop of contraction. What is required over and\nabove organic substances and cell-forms, is that special state called\n_organization_. See \u00a7 49.\n\nThose who contemplate the manifestations without also taking into\naccount their modes of production may see nothing but physico-chemical\nfacts in vital facts. It is by a similar limitation of the point of\nview that Vitality is often confounded with Movement, and portions\nof organic matter are said to live, simply on the evidence of their\nmovements.[7]\n\n\n\n\nCHAPTER II.\n\nDEFINITIONS OF LIFE.\n\n\n25. Biology, the science of Life, being thus assigned its place in the\nhierarchy of objective laws, we now proceed to consider what the term\nLife symbolizes.\n\nBy a large preliminary simplification, Life may be defined as _the\nmode of existence of an organism in relation to its medium_. To render\nthis of any value, however, a clear conception of the organism is\nfirst indispensable; and this must be preceded by an examination of\nthe various attempts to define life in anticipation of such a clear\nconception.\n\n26. Every phenomenon, or group of phenomena, may be viewed under\ntwo aspects--the _statical_, which considers the conditions of\nexistence; and the _dynamical_, which considers these conditions in\ntheir resultant,--in their _action_. The statical definition of Life\nwill express the connexus of the properties of organized substance,\nall those conditions, of matter, form, and texture, and of relation\nto external forces, on which the organism depends. These various\nconditions, condensed into a single symbol, constitute Vitality or\nVital Force, and are hence taken as the Cause of vital phenomena.\nThe dynamical definition will express the connexus of Functions and\nFaculties of the organism, which are the statical properties of\norganized substance in action, under definite relations.\n\nIt is obvious that the term Life must vary with the varying\nsignificates it condenses,--every variation in the complexity of the\norganism will bring a corresponding fulness in the signification of\nthe term. The life of a plant is less significant than the life of\nan animal; and the life of a mollusc less than that of a fish. But\nnot only is the term one of varying significance, it is always an\nabstract term which drops out of sight particular concrete differences,\nregistering only the universal resemblances.\n\n       *       *       *       *       *\n\n27. It would be a profitless labor to search out, and a wearisome\ninfliction to set down, the various definitions which have been\nproposed and accepted; but certain characteristic examples may be\nselected. All that I am acquainted with belong to two classes: 1\u00b0, the\n_meta_-physiological hypothesis of an _extra_-organic agent, animating\nlifeless matter by unknown powers; 2\u00b0, the physiological hypothesis\nwhich seeks the cause of the phenomena (i.\u00a0e. the conditions) _within_\nthe organism itself,--a group of conditions akin to those manifested\nelsewhere, but differently combined. The first hypotheses are known\nunder the names of Animism and Vitalism,--more commonly the latter. The\nsecond are known as Organicism and Materialism,--but the latter term\nonly applies to some of the definitions.\n\n28. Under Vitalism are included all the hypotheses of a soul, a spirit,\nan arch\u00e6us, a vital principle, a vital force, a _nisus formativus_,\na plan or divine idea, which have from time to time represented the\nmetaphysical stage of Biology. The characteristic of that stage is\nthe personification of a mystery, accompanied by the persuasion that\nto name a mystery is to explain it. In all sciences when processes\nare imperfectly observed, the _theory_ of the processes (which is a\nsystematic survey of the available evidence marshalled in the order\nof causal dependence) is supplemented by _hypothesis_, which fills up\nwith a guess the gap left by observation. The difference between the\nmetaphysical and the positive stages of a science lies in the kind of\nguess thus introduced to supplement theory, and the degree of reliance\naccorded to it. I have more than once insisted on the scientific\ncanon that \u201cto be valid, an explanation must be expressed in terms of\nphenomena already observed\u201d; now it is quite clear that most of the\nextra-organic hypotheses do not fulfil this condition; no one having\never _observed_ a spirit, an arch\u00e6us, or a vital principle; but only\n_imagined_ these agents to explain the facts observed. As an example of\nthe difference, and a proof that the value of an hypothesis does not\nrest on the facility with which it connects observations, and seems\nto explain them, take the three hypotheses of animal spirits, nervous\nfluid, and electricity, by which neural processes have been explained.\nThe animal spirits are imaginary; the nervous fluid is without a basis\nin observation, no evidence of such a fluid having been detected;\nbut electricity (or, speaking rigorously, the movements classed as\nelectrical), although not proved to be _the_ agent in nerve-action,\nis proved to exist in nerves as elsewhere, and its modes of operation\nare verifiable. It, therefore, and it alone of the three hypotheses,\nis in conformity with the scientific canon. It may not, on full\ninvestigation, meet all requirements; it may be rejected as imperfect;\nbut it is the kind of guess which scientific theory demands.\n\nThe second difference noticeable between the metaphysical and the\npositive stages is the degree of reliance accorded to hypothesis;\nwhich is very much the same as that noticeable in the uncritical and\ncritical attitudes of untrained and trained intellects. The one accepts\na guess as if it were a proof; is fascinated by the facility of linking\ntogether isolated observations, and, relying on the guess as truth,\nproceeds to deduce conclusions from it; the other accepts a guess as\nan aid in research, trying by its aid to come upon some observation\nwhich will reveal the hidden process; but careful never to allow the\nguess to _supersede observation_, or to form a basis of deductions not\nimmediately verified.\n\n29. A glance at the metaphysiological definitions will detect both the\nkind of guess and the kind of reliance which prevailed. The mystery\nwas not simply recognized, it was personified as an entity: Will and\nIntelligence were liberally accorded to it, for it was supposed to\nshape matter, and direct force into predestined paths by prescience of\na distant end. The observed facts of the egg passing through successive\nchanges into a complex organism were so marvellous, so unlike any\nfacts observable in the inorganic world, that they seemed to demand a\ncause drawn from higher sources. The mystery of life obtruded itself\nat every turn. It was named, and men fancied it explained. But in\ntruth no mystery is got rid of by explanation, however valid; it is\nonly shifted farther back. Explanation is the resolution of a complex\nphenomenon into its conditions of existence--the product is reduced to\nits factors; the explanation is final when this resolution has been\nso complete that a reconstruction of the product is possible from\nthe factors. The vast majority of explanations--especially in the\norganic region--are no more than what mathematicians call \u201ca first\napproximation.\u201d It is through successive approximations that science\nadvances; but even when the final stage is reached a mystery remains.\nWe may know that certain elements combine in certain proportions\nto produce certain substances; but why they produce these, and not\ndifferent substances, is no clearer than why muscles contract or\norganisms die. This Why is, however, an idle question. That alone which\ntruly concerns us is the How, and not the Why.\n\n30. Biology is still a long way off the How. But it can boast of\nmany approximations; and its theories are to be tested by the degree\nof approximation they effect. In this light the physiological,\n_intra_-organic, hypotheses manifestly have the advantage. Many of them\nare indeed very unacceptable; they are guided by a mistaken conception\nof the truths reached by Analysis. For when men first began to discard\nthe extra-organic hypotheses, and to look into the organism itself,\nthey were so much impressed by the mechanical facts observed, that they\nendeavored to reduce all the phenomena to Mechanics. The circulation\nbecame simply a question of hydraulics. Digestion was explained as\ntrituration. The chemists then appeared, and their shibboleths were\n\u201caffinities\u201d and \u201coxidations.\u201d With Bichat arose the anatomical school,\nwhich decomposing the organism into organs, the organs into tissues,\nand these tissues into their elements, sought the analytical conditions\nof existence of the organism in the properties of these tissues, and\nthe functions of these organs. The extra-organic agent was thus finally\nshown to be not only a fiction, but a needless fiction.\n\nEvery student of the history of the science will note how from the very\nnecessities of the case the metaphysiologists, without relinquishing\ntheir Vital Principle, have been led more and more to enter on the\ntrack of the physiologists, pursuing their researches more and more\ninto the processes going on in the organism, and assigning more and\nmore causal efficiency to these, with a corresponding restriction\nof the province of their extra-organic cause. Hence in the ranks of\nthe vitalists have been found some of the very best observers and\ntheorists; but they were such in despite of, and not in consequence\nof, their hypothesis, which was only invoked by them when evidence\nwas at fault. Nor, unscientific as vitalism is, can we deny that it\nhas been so far serviceable to the science, that it has corrected the\nmaterialist error of endeavoring to explain organic phenomena by\nphysico-chemical laws; and has persistently kept in view the radical\ndifference between organic and inorganic.\n\n31. These remarks may justify a selection of definitions, classified\nunder the two heads. The selection is fitly opened by the Aristotelian\ndefinition which prevailed for centuries.\n\nAristotle distinguishes Life, which he says means \u201cthe faculties of\nself-nourishment, self-development, and self-decay,\u201d from the Vital\nPrinciple. Every natural body manifesting life may be regarded as an\nessential existence (\u03bf\u1f50\u03c3\u03af\u03b1); but _then it is an existence only as a\nsynthesis_ (\u1f61\u03c2 \u03c3\u03c5\u03b8\u03ad\u03c4\u03b7); and since an organism is such a synthesis,\nbeing possessed of Life, it cannot be the Vital Principle (\u03c8\u03c5\u03c7\u03ae).\nTherefore it follows that the Vital Principle must be an essence, as\nbeing the Form of a natural body holding life in _potentiality_. The\nVital Principle is the primary reality of an organism. \u201cIt is therefore\nas idle to ask whether the Vital Principle and Organism are one, as\nwhether the wax and the impress on it are one.... Thus if an eye\nwere an animal, Vision would be its Vital Principle: for Vision is,\nabstractedly considered, the essence of the eye; but the eye is the\nbody of Vision, and if Vision be wanting, then, save in name, it is no\nlonger an eye.\u201d\n\nApart from certain metaphysical implications, inevitable at that\nperiod, there is profound insight in this passage. His adversary\nTelesio quite misconceives the meaning here assigned to the Vital\nPrinciple.[8]\n\n32. Let us pass over all the intermediate forms of the hypothesis, and\ndescend to Kant, who defines Life \u201can internal principle of action\u201d\n(this does not distinguish it from fermentation); an organism he says\nis \u201cthat in which every part is at once means and end.\u201d \u201cEach part\nof the living body has its cause of existence in the whole organism;\nwhereas in non-living bodies each part has its cause in itself.\u201d\nJohannes M\u00fcller adopts a similar view: \u201cThe harmonious action of the\nessential parts of the individual subsist only by the influence of a\nforce, the operation of which is extended to all parts of the body,\nand does not depend on any single parts; this _force must exist before\nthe parts_, which are in fact formed by it during the development of\nthe embryo.... The vital force inherent in them generates from the\norganic matter the essential organs which constitute the whole being.\nThis _rational creative force_ is exerted in every animal strictly in\naccordance with what the nature of each requires.\u201d\n\n33. This is decidedly inferior to Aristotle, who did not confound\nthe vegetative with the rational principle. It rests on the old\nmetaphysical error of a _vis medicatrix_, an error which cannot\nsustain itself against the striking facts which constantly point to\na _vis destructrix_, a destructive tendency quite as inexorable as\nthe curative tendency. And the experimental biologist soon becomes\nimpressed with the fact that the tissues have indeed a _selective_\naction, by which from out the nutrient material only these substances\nare assimilated which will enter into combination with them; but this\nselective action is fatal, no less than reparative: substances which\npoison the tissue are taken up as readily as those which nourish\nit. The idea of prescience, therefore, cannot be sustained; it is\nindeed seldom met with now in the writings of any but the Montpellier\nschool, who continue the traditions of Stahl\u2019s teaching. It has been\nso long exploded elsewhere that one is surprised to find an English\nphysiologist clinging to a modification of it--I mean Dr. Lionel Beale,\nwho repeatedly insists on Life as \u201ca peculiar Force, _temporarily\nassociated_ with matter,\u201d a \u201cpower capable of controlling and directing\nboth matter and force,\u201d an \u201c_undiscovered_ form of force _having no\nconnection with primary energy or motion_.\u201d \u201cThe higher phenomena of\nthe nervous system are probably due primarily to the movements of the\ngerminal matter due to vital power, which vital power of this the\nhighest form of germinal matter is in fact the living _I_.\u201d\n\n34. Apart from the primary objection to all these definitions,\nnamely, that they seek to express organic phenomena in terms of an\nextra-organic principle, to formulate the facts _observed_ in terms\nof a cause _inferred_, there is the fatal objection that they speak\nconfidently on what is avowedly unknown. If the force be, as Dr. Beale\nsays, \u201cundiscovered,\u201d on what grounds can he assert that it has _no_\nconnection with the forces which are known? All that the observed facts\nwarrant is the assertion that organic phenomena are special (which\nno one denies), and must therefore depend on special combinations of\nmatter and force. But on this ground we might assume a crystallizing\nForce, and a coagulating Force, having no connection with the molecular\nforces manifested elsewhere: these also are special phenomena, not to\nbe confounded with each other.\n\n35. Schelling defines Life as \u201ca principle of individuation\u201d and a\n\u201ccycle of successive changes determined and fixed by this internal\nprinciple.\u201d Which is so vague that it may be applied in very different\nsenses. Bichat\u2019s celebrated definition (which is only a paraphrase of\na sentence in Stahl), \u201cthe sum of the functions which resist Death,\u201d\nalthough an endeavor to express the facts from the Intra-organic point\nof view, is not only vague, but misrepresents one of the cardinal\nconditions, by treating the External Medium as antagonistic to Life,\nwhereas Life is only possible in the relation to a Medium.\n\n36. Were it not so vague, the definition proposed by Dug\u00e8s and B\u00e9clard\nwould be unexceptionable: the former says it is \u201cthe special activity\nof organized beings\u201d; the latter, \u201cthe sum of the phenomena proper to\norganized bodies.\u201d When supplemented by a description of organized\nbodies, these formul\u00e6 are compendious and exact. The same remark\napplies to the definition of Lamarck: \u201cthat state of things which\npermits organic movements; and these movements, which constitute active\nlife, result from a stimulus which excites them.\u201d\n\n37. De Blainville, and after him Comte and Charles Robin, define\nit thus: \u201cLife is the twofold internal movement of composition and\ndecomposition at once general and continuous.\u201d This, excellent as\nregards what is called vegetal life, is very properly objected to by\nMr. Herbert Spencer in that it excludes those nervous and muscular\nfunctions which are the most conspicuous and distinctive of vital\nphenomena. The same objection must be urged against Professor Owen\u2019s\ndefinition: \u201cLife is a centre of intussusceptive assimilative force\ncapable of reproduction by spontaneous fission.\u201d\n\n38. In 1853, after reviewing the various attempts to express in a\nsentence what a volume could only approximately expound, I proposed the\nfollowing: \u201cLife is a series of definite and successive changes, both\nof structure and composition, which take place within an individual\nwithout destroying its identity.\u201d This has been criticised by Mr.\nHerbert Spencer and by Dr. Lionel Beale, and if I had not withdrawn\nit before their criticisms appeared, I should certainly have modified\nand enlarged it afterwards. I mention it, however, because it is an\napproach to a more satisfactory formula in so far as it specifies two\ncardinal characteristics distinguishing organisms from all anorganisms,\nnamely, the incessant evolution through definite stages, and the\npreservation of specific integrity throughout the changes; not only\nthe organism as a whole is preserved amidst incessant molecular\nchange, but each tissue lives only so long as the reciprocal molecular\ncomposition and decomposition persist. On both of these points I shall\nhave to speak hereafter. The definition, however, is not only defective\nin its restriction to the molecular changes of Nutrition, taking no\naccount of the Properties and Functions of the organism; but defective\nalso in giving no expression to equally important relations of the\norganism to the medium.\n\n39. This last point is distinctly expressed in Mr. Spencer\u2019s\ndefinition: \u201cLife is the continuous adjustment of internal relations\nto external relations.\u201d Considered as a formula of the most general\nsignificance, embracing therefore what is common to all orders of vital\nphenomena, this is the best yet proposed.[9] If I propose another it\nwill not be to displace but to run alongside with Mr. Spencer\u2019s; and\nthis only for more ready convenience. Before doing so I must say a few\nwords by way of clearing the ground.\n\n40. What does the term Life stand for? What are the concrete\nsignificates of this abstract symbol? As before stated, it is sometimes\na compendious shorthand for the special phenomena distinguishing living\nfrom non-living bodies; and sometimes it expresses not these observed\nphenomena, but their conditions of existence, which are by one school\npersonified in an abstract and extra-organic cause. Thus the life of\nan animal, a man, or a nation, means--1\u00b0, the special manifestations\nof these organisms, and groups of organisms; or 2\u00b0, the causes which\nproduce these manifestations. We are often misunderstood by others, and\nsometimes vague to ourselves, when we do not bear these two different\nmeanings in view. It was probably some sense of this which made\nAristotle distinguish Vitality from Life, as that of the one uniform\ncause separated from its multiple effects; it was certainly the motive\nof Fletcher, who thus expressly limits the meanings: \u201c_Vitality_ or\n_Irritability_, the property which characterizes organized beings\nof being acted on by certain powers otherwise than either strictly\nmechanically or strictly chemically; _Life_, the sum of the actions\nof organized beings resulting directly from their vitality so acted\non.\u201d[10]\n\nVitality and Life being thus discriminated as the statical and\nthe dynamical aspects of the organism, we find in relation to the\nformer two radically opposed conceptions: the metaphysiological or\nextra-organic, and the physiological or intra-organic. The first\nconceives Vitality to be a Vital Principle, or extra-organic agent,\nsometimes a soul, spirit, arch\u00e6us, idea, and sometimes a force, which\neasily becomes translated into a property.\n\nThe conception of an entity must be rejected, because it is\nmetempirical and unverifiable, \u00a7 34. The conception of a force must\nbe rejected, because it is irreconcilable with any definite idea we\nhave of force. What the term Force signifies in Physics and Chemistry,\nnamely, mass animated by velocity, or _directed pressure_, which is\nthe activity of the agent,--is precisely that which these vitalists\npertinaciously exclude. They assume a force which has nothing in\ncommon with mass and velocity; which is _not a resultant, but a\nprinciple_; which instead of being a _directed quantity_, is itself\nautonomous and _directive_, shaping matter into organization, and\nendowing it with powers not assignable to matter. If this vital force\nhas any mass at its back, it is a spiritual mass; if it is directed,\nthe direction issues from a \u201cMind somewhere.\u201d Now this conception is\npurely metempirical. Not only is it inexact to speak of Vitality as\na force, it is almost equally inexact to speak of it as a property;\nsince it is a term which includes a variety of properties; and when\nFletcher assigns the synonym of Irritability, this at once reveals the\ninexactness; for beside this property, we must place Assimilation,\nEvolution, Disintegration, Reproduction, Contractility, and\nSensibility,--all characteristic properties included in Vitality.\n\n41. Having thus rejected the conceptions of entity, force, and\nproperty, we are left in presence of--1\u00b0, the organic conditions as the\nelements, and 2\u00b0, of their synthesis (in the state called organization)\nas the personified principle. Vital forces, or the vital force, if\nwe adopt the term for brevity\u2019s sake, is a _symbol of the conditions\nof existence of organized matter_; and since organisms are specially\ndistinguishable from anorganisms by this speciality of their synthesis,\nand not by any difference in the nature of the elements combined, this\nstate of organization is the \u201cforce\u201d or \u201cprinciple\u201d of which we are in\nquest. To determine what Life means, we must observe and classify the\nphenomena presented by living beings. To determine what Vitality--or\norganization--means, we must observe and classify the processes which\ngo on in organized substances. These will occupy us in the succeeding\nchapters; here I may so far anticipate as to propose the following\ndefinitions:--\n\n42. Life is the functional activity of an organism in relation to\nits medium, as a synthesis of three terms: Structure, Aliment, and\nInstrument; it is the sum of functions which are the resultants of\nVitality; Vitality being the sum of the properties of matter in the\nstate of organization.\n\n43. Vital phenomena are the phenomena manifested _in_ organisms when\nexternal agencies disturb their molecular equilibrium; and _by_\norganisms when they react on external objects. Thus everything done in\nan organism, or by an organism, is a vital act, although physical and\nchemical agencies may form essential components of the act. If I shrink\nwhen struck, or if I whip a horse, the blow is in each case physical,\nbut the shrinking and the striking are vital.\n\nEvery part of a living organism is therefore vital, as _pertaining_\nto Life; but no part has this Life when isolated; for Life is the\nsynthesis of all the parts: a federation of the organs when the\norganism is complex, a federation of the organic substances when the\norganism is a simple cell.\n\n44. All definitions, although didactically placed at the introduction\nof a treatise, are properly the final expression of the facts which\nthe treatise has established, and they cannot therefore be fully\napprehended until the mind is familiarized with the details they\nexpress. Much, therefore, which to the reader may seem unintelligible\nor questionable in the foregoing definition, must be allowed to pass\nuntil he has gone through the chapters which follow.\n\n\n\n\nCHAPTER III.\n\nORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE.\n\n\n45. There is a marked difference between organ_ic_ and organ_ised_\nsubstances. The organic are non-living, though capable of living\nwhen incorporated in organized tissue (albumen is such a substance);\nor they may be incapable of living because they have lived, and are\nproducts of waste, e.\u00a0g. urea. The organized substance is a specific\ncombination of organic substances of various kinds, a combination\nwhich is organization. Any organized substance is therefore either an\nindependent organism, or part of a more complex organism. Protoplasm,\neither as a separate organism or as a constituent of a tissue, is\norganized substance.\n\nOrganic substances are numerous and specific. They are various\ncombinations of proximate principles familiar to the chemist, which may\nconveniently be ranged under three classes: The first class of organic\nsubstances comprises those composed of principles having what is called\na mineral origin; these generally quit the organism unchanged as they\nentered it. The second class comprises those which are crystallizable,\nand are formed _in_ the organism, and generally quit it in this state\nas excretions. The third class comprises the colloids, i.\u00a0e. substances\nwhich are coagulable and not crystallizable, and are formed in and\ndecomposed in the organism, thus furnishing the principles of the\nsecond class. All the principles are in a state of solution. Water is\nthe chief vehicle of the materials which enter and the materials which\nquit the organism; and bodies in solution are solvents of others, so\nthat the water thus acquires new solvent properties.\n\n45_a_. Two points must be noted respecting organic substances: they are\nmostly combinations of _higher multiples_ of the elements; and their\ncombinations are not _definite_ in quantity. Albumen, for example,\nhas (according to one of the many formulas which have been given) an\nelementary composition of 216 atoms of Carbon, 169 of Hydrogen, 27 of\nNitrogen, 3 of Sulphur, and 68 of Oxygen; whereas in its final state,\nin which it quits the organism as Urea, it is composed of 2 atoms\nof Carbon, 4 of Hydrogen, 2 of Nitrogen, and 2 of Oxygen, all the\nSulphur having disappeared in other combinations. In like manner in\nthe organism Stearin falls from C_{114}, H_{110}, O_{12}, to Oxalic\nAcid, which is C_{4}, H_{2}, O_{8}. It is obvious that the necessary\nmodifiability of organic substance is due to this multiplicity of its\nelementary parts and the variety of its molecular structure.\n\n45_b_. Nor is the indefiniteness of the quantitative composition less\nimportant, though seldom adequately appreciated, or even suspected.\nRobin and Verdeil[11] are the only writers I can remember who have\ndistinctly brought the fact into prominence. That all inorganic\nsubstances are definite in composition, every one knows. Quicklime,\nfor example, may be got from marble, limestone, oyster-shells, or\nchalk; but however produced, it always contains exactly 250 ounces\nof calcium to 100 ounces of oxygen; just as water is always OH_{2}.\nNot so the pre-eminently vital substances, those which are coagulable\nand not crystallizable: no precise formula will express one of these;\nfor the same specific substance is found to vary from time to time,\nand elementary analyses do not give uniform results. Thus, if after\ncausing an acid to combine with one of these substances, we remove\nthe acid, we are not certain of finding the substance as it was\nbefore--as we are, for example, after urea is combined with nitric\nacid and then decomposed. The same want of definiteness is of course\neven more apparent in the _combinations_ of these proximate principles\ninto organized substance. Protoplasm differs greatly in different\nplaces. Epithelial cells differ. Muscular and nervous fibres are never\nabsolutely the same in different regions. A striped and unstriped\nmuscular fibre, the muscular fibre of a sphincter or of a limb, a\nnerve-fibre in a centre, in a trunk, or in a gland, will present\nvariations of composition. The elastic fibres of the ligaments are\nlarger in the horse than in man; and in other animals they are smaller.\nThese differences are sometimes due to the constituents, and sometimes\nto the arrangement of the constituents; the conversion of Albumen into\nFibrine without elementary loss or addition, is a good example of the\nlatter. That the tissues of one man are not absolutely the same as\nthe tissues of another, in the sense in which it is true to say that\nthe chalk of one hill is the same as that of another, or as gold in\nAustralia is the same as gold in Mexico, is apparent in their very\ndifferent reactions under similar external conditions: the substance\nwhich poisons the one leaves the other unaffected. The man who has once\nhad the small-pox, or scarlet fever, is never the same afterwards,\nsince his organism has now become insusceptible of these poisons. And\nSir James Paget has called attention to the striking fact revealed in\ndisease, namely, that in the same tissue--say the bone or the skin--a\nmorbid substance fastens only on certain small portions leaving all\nthe rest unaltered, but fastens on exactly corresponding spots of the\nopposite sides of the body; so that on both arms, or both legs, only\nthe corresponding bits of tissue will be diseased. \u201cManifestly when\ntwo substances display different relations to a third their composition\ncannot be identical; so that though we may speak of all bone or\nof all skin as if it were all alike, yet there are differences of\nintimate composition. No power of artificial chemistry can detect the\ndifference; but a morbid material can.\u201d[12] It is to this variability\nof composition that we must refer individual peculiarities, and those\nstriking forms of variety known as idiosyncrasies, which cause some\norganisms to be affected by what seem inexplicable influences--physical\nand moral.\n\nIn spite of all these variations, however, there are certain specific\nresemblances dependent of course on similarity of composition and\nstructure, so that the muscle of a crustacean is classed beside the\nmuscle of a vertebrate, although the elementary analysis of the two\nyields different results. Nerve-tissue, according to my experience,\nis the most variable of all, except the blood; variable not only from\nindividual to individual, and from genus to genus, but even in the same\nindividual it never contains the same quantities of water, phosphates,\netc. Hence it is that different nerves manifest different degrees of\nexcitability, and the same nerve differs at different times. Thus the\nfifth pair, in a poisoned animal, retains its excitability long after\nthe others are paralyzed; and the patient under chloroform feels a\nprick on the brow or at the temples, when insensible at any other spot.\nThe pneumogastric which is excitable during digestion is--in dogs at\nleast--inexcitable when the animal is fasting.\n\n46. The organic substances are what analysis discovers in organized\nsubstances, but none of them, not even the highest, is living, except\nas organized. Albumen alone, or Stearin alone, is as incapable of\nVitality, as Plumbago, or Soda; but all organic substances are\ncapable of playing a part in vital actions; and this part is the\nmore important in proportion to their greater molecular variety.\nOrganization is a special synthesis of substances belonging to all\nthree classes; and the organized substance, thus formed, alone merits\nthe epithet living. We see how organized substances, being constituted\nby principles derived from the inorganic world, and principles derived\nfrom the organic world, have at once a dependence on the external\nMedium, and an independence of it, which is peculiar to living beings.\nAn analogous dependence and independence is noticeable with respect to\nthe parts; and this is a character not found in inorganic compounds.\nThe organism, even in its simplest forms, is a structure of different\nsubstances, each of which is complex. While one part of a crystal is\natomically and morphologically identical with every other, and is the\nwhole crystal \u201cwrit small,\u201d one part of an organism is unlike another,\nand _no part_ is like the whole. Hence the dependence of one organ and\none tissue on another, and each on all. Yet, while every part is, so to\nspeak, a condition of existence of every other, and the unity of the\norganism is but the expression of this solidarity,--wherever organized\nsubstance has been differentiated into morphological elements (cells,\netc.), each of these has its own course of evolution independently of\nthe others,--is born, nourished, developed, and dies.\n\n47. The interdependence of nerve and muscle is seen in this, that the\nmore the muscle is excited the feebler its contractions become; this\ndecrease in contractility is compensated by an increased excitability\nin its nerve; so that while the muscle demands a more powerful\nstimulus, the nerve acquires a more energetic activity. Ranke\u2019s curious\nand careful experiments seem to prove that this depends on the wearied\nmuscle absorbing more water, owing to the acids developed by its\nactivity, and on the nerve losing this water--a nerve being always\nmore irritable when its quantity of water diminishes.\n\n48. Herein we see illustrated the great law of organized activity,\nthat it is a simultaneity of opposite tendencies, as organized matter\nis a synthesis of compositions and decompositions, always tending\ntowards equilibrium and disturbance, storing up energy and liberating\nit. Unlike what is observed in unorganized matter, the conditions of\nwaste bring with them conditions of repair, and thus--within certain\nlimits--every loss in one direction is compensated by gain in another.\nThere is a greater flow of nutrient material, or, more properly\nspeaking, a greater assimilation of it by the tissue, where there has\nbeen made a greater opening for it by previous disintegration. The\nalkaline state of the nutrient material, and the acid state of the\nmaterial that has been used,--the alkaline state which characterizes\nrepose and assimilation, and the acid state which characterizes\nactivity and deassimilation, are but cases of this general law; on the\nsynthesis of these opposite tendencies depends the restless change,\ntogether with the continued specific integrity, of organized matter.\n\n49. The state of organization may therefore be defined as the\n_molecular union of the proximate principles of the three classes\nin reciprocal dissolution_. An organism is formed of matter thus\norganized, which exists in two states--the _amorphous_ and the\n_figured_. The amorphous substances are liquid, semi-liquid, and solid;\nthe figured are the cells, fibres, and tubes, called \u201canatomical\nelements.\u201d For these I prefer the term suggested, I believe, by Milne\nEdwards, namely, _organites_, because they are the individual elements\nwhich mainly constitute the organs, and are indeed by many biologists\nconsidered as elementary organisms. These organites, which go to form\nthe tissues, and by the tissues the organs, have their specific form,\nvolume, structure, and chemical reactions. They exist in textures\nor tissues, or separately (e.\u00a0g. blood corpuscles), and are in many\nrespects like the simplest organisms known, such as Monads, Vibrios,\nAm\u0153b\u00e6, etc.\n\n50. The simplest form of life is not--as commonly stated--a cell, but\na microscopic lump of jelly-like substance, or protoplasm, which has\nbeen named _sarcode_ by Dujardin, _cytode_ by Haeckel, and _germinal\nmatter_ by Lionel Beale. This protoplasm, although entirely destitute\nof texture, and consequently destitute of organs, is nevertheless\nconsidered to be living, because it manifests the cardinal phenomena\nof Life: Assimilation, Evolution, Reproduction, Mobility, and\nDecay. Examples of this simplest organism are Monads, Protam\u0153b\u00e6,\nand Polythalamia.[13] Few things are more surprising than the vital\nactivity of these organites, which puzzle naturalists as to whether\nthey should be called plants or animals. All microscopists are familiar\nwith the spectacle of a formless lump of albuminous matter (a Rhizopod)\nputting forth a process of its body as a temporary arm or leg, or else\nslowly wrapping itself round a microscopic plant, or morsel of animal\nsubstance, thus converting its whole body into a mouth and a stomach;\nbut these phenomena are surpassed by those described by Cienkowski,[14]\nwho narrates how one Monad fastens on to a plant and sucks the\nchlorophyll first from one cell and then from another; another Monad,\nunable to make a hole in the cell-wall, thrusts long processes of its\nbody into the opening already made, and drags out the remains of the\nchlorophyll left there by its predecessor; while a third Monad leads a\npredatory life, falling upon other Monads that have filled themselves\nwith food. Here, as he says, we stand on the threshold of that dark\nregion where Animal Will begins; and yet there is here only the\nsimplest form of organization.[15]\n\n51. Now let our glance pass on to the second stage--the Cell. Here we\nhave a recognized differentiation in the appearance of a nucleus amid\nthe protoplasm. The nucleus is chemically different from the substance\nwhich surrounds it; and although perhaps exaggerated importance has\nbeen attributed to this nucleus, and mysterious powers have been\nascribed to it, yet as an essential constituent of the cell it commands\nattention. Indeed, according to the most recent investigations, the\ndefinition of a cell is \u201ca nucleus with surrounding protoplasm.\u201d The\ncell-wall, or delicate investing membrane--that which makes the cell a\nclosed sac--is no longer to be regarded as a necessary constituent, but\nonly as an accessory.[16]\n\n52. The cell may be either an organism or an organite. It may lead an\nisolated life as plant or animal, or it may be united with others and\nlead a more or less corporate existence; but always, even as an element\nof a higher organism, it preserves its own individuality. At first we\nsee that the corporate union is very slight, merely the contact of one\ncell with another of its own kind, as in the filament of a Conferva.\nRising higher, we see the cell united with others different from\nit; plants and animals appear, having structures composed of masses\nof various cells. Rising still higher, we see animal forms of which\nthe web is woven out of myriads upon myriads of cells, with various\ncell-products, processes, fibres, tubes.\n\n\nORGANISM AND MEDIUM.\n\n53. But we have only one half of the great problem of life, when we\nhave the organism; and it is to this half that the chief researches\nhave been devoted, the other falling into neglect. What is that\nother? The Medium in which the organism lives. Every individual\nobject, organic or inorganic, is the product of two factors:--first,\nthe relation of its constituent molecules to each other; secondly,\nthe relation of its substance to all surrounding objects. Its\nproperties, as an object or an organism, are the results of its\nconstituent molecules, and of its relation to external conditions.\nOrganisms are the results of a peculiar group of forces, exhibiting\na peculiar group of phenomena. Viewing these in the abstract, we\nmay say that there are three regulative laws of life:--(1) The _Lex\nFormationis_--the so-called _nisus formativus_, or \u201corganizing force\u201d;\n(2) the _Lex Adaptationis_, or adaptive tendency; (3) the _Lex\nHereditatis_, or tendency to reproduce both the original form and its\nacquired modifications. We have always to consider the organizing\nforce in relation to all surrounding forces--a relation succinctly\nexpressed in the word Adaptation. Just as water is water only under a\ncertain relation of its constituent molecules to the temperature and\natmospheric pressure--just as it passes into other forms (ice or steam)\nin adapting itself to other conditions; so, likewise, the organism only\npreserves its individuality by the adjustment of its forces with the\nforces which environ it.\n\n54. This relation of Organism and Medium, the most fundamental of\nbiological data, has had a peculiar fortune: never wholly unrecognized,\nfor it obtrudes itself incessantly in the facts of daily experience,\nit was very late in gaining recognition as a principle of supreme\nimportance; and is even now often so imperfectly apprehended that one\nschool of philosophers indignantly rejects the idea of the Organism and\nMedium being the two factors of which Life is the product. Not only\nis there a school of vitalists maintaining the doctrine of Life as an\nentity independent both of Organism and Medium, and using these as its\ninstruments; but there is also a majority among other biologists, who\nbetray by their arguments that they fail to keep steadily before them\nthe fundamental nature of the relation. Something of this is doubtless\ndue to the imperfect conception they have formed of what constitutes\nthe Medium; instead of recognizing in it the sum of external conditions\naffecting the organism--i.\u00a0e. the sum of the relations which the\norganism maintains with external agencies,--they restrict, or enlarge\nit, so as to misapprehend its significance--restrict it to only a few\nof the conditions, such as climate, soil, temperature, etc., or enlarge\nit to embrace a vast array of conditions which stand in no directly\nappreciable relation to the organism. Every one understands that an\norganism is dependent on proper food, on oxygen, etc., and will perish\nif these are withheld, or be affected by every variation in such\nconditions. Every one understands that an animal which can devour or be\ndevoured by another, will flourish or perish according to the presence\nof its prey or its enemy. But it is often forgotten that among external\nexistences, all those which stand in no appreciable relation to the\norganism are not properly to be included in its Medium. In consequence\nof this oversight we frequently hear it urged as an objection to the\nEvolution Hypothesis, that manifold organisms exist under the _same_\nexternal conditions, and that organisms persist unchanged amid a\ngreat variety of conditions. The objection is beside the question. In\nthe general sum of external forces there are certain items which are\nnearly related to particular organisms, and constitute their Medium;\nthose items which are so distantly related to these organisms as to\ncause no reactions in them, are, for them, as if non-existent.[17] Of\nthe manifold vibrations which the ether is supposed to be incessantly\nundergoing, only certain vibrations affect the eye as light; these\nconstitute the Medium of Sight; the others are as if they were not.\nOnly certain vibrations of the air affect the ear as Sound; to all\nother vibrations we are deaf; though ears of finer sensibility may\ndetect them and be deaf to those which affect us.\n\n55. \u201cThe external conditions of existence\u201d is therefore the correct\ndefinition of the Medium. An animal may be surrounded with various\nfoods and poisons, but if its organism is not directly affected by them\nthey cannot be food or poison to it. An animal may be surrounded with\ncarnivorous rivals, but if it is not adapted to serve them as food, or\nis too powerful to be attacked by them, they only indirectly enter into\nits Medium, by eating the food it would eat. The analogy is similar\nwith anorganisms and their relation to their media. Every physical or\nchemical phenomenon depends on the concurrence of definite conditions:\nnamely, the substance which manifests the change, and the medium in\nwhich the change is manifested. Alter the medium, solid, liquid, or\ngaseous, change its thermal or electrical state, and the phenomenon is\naltered. But although similar alterations in the medium notoriously\ninfluence the organism, yet, because a great many variations in\nexternal conditions are unaccompanied by appreciable changes in the\norganism, there are biologists who regard this as a proof of Life being\nindependent of physical and chemical laws; an error arising from their\nnot recognizing the precise nature of organic conditions.\n\n56. To give greater precision to the conception of a Medium it will\nbe desirable to adopt the distinction much insisted on by Claude\nBernard, namely, 1\u00b0, an External or Cosmical Medium, embracing the\nwhole of the circumstances outside the organism, capable of directly\naffecting it, and 2\u00b0, an Internal or Physiological Medium, embracing\nthe conditions inside the organism, and in direct relation with\nit--that is to say, the plasma in which its tissues are bathed, by\nwhich they are nourished. To these add its temperature and electrical\nconditions. Bernard only includes the nutritive fluid; but inasmuch as\neach organism possesses a temperature and electrical state of its own,\nand these are only indirectly dependent on the external temperature\nand electricity, and as it is with these internal conditions that\nthe organism is in direct relation, I include them with the plasma\namong the constituents of the Physiological Medium. Any change in the\nExternal Medium, whether of temperature or electricity, of food or\nlight, which does not disturb the Internal Medium, will of course leave\nthe organism undisturbed; and for the most part all the changes in\nthe External Medium which do affect the organism, affect it by first\nchanging the Internal Medium. External heat or cold raises or depresses\nthe internal temperature _indirectly_ by affecting the organic\nprocesses on which the internal temperature depends. We see here the\nrationale of acclimatization. Unless the organism can adapt itself to\nthe new External Medium by the readjustment of its Internal Medium, it\nperishes.\n\n57. We are now enabled to furnish an answer to the very common\nobjection respecting the apparent absence of any direct influence of\nexternal conditions. Let the objection first be stated in the words\nof a celebrated naturalist, Agassiz: \u201cIt is a fact which seems to be\nentirely overlooked by those who assume an extensive influence of\nphysical causes upon the very existence of organized beings, that the\nmost diversified types of animals and plants are everywhere found under\nidentical circumstances. The smallest sheet of fresh water, every\npoint of the sea-shore, every acre of dry land, teems with a variety\nof animals and plants. The narrower the boundaries which are assigned\nas the primitive home of all these beings, the more uniform must be\nthe conditions under which they must be assumed to have originated; so\nuniform indeed that in the end the inference would be that the same\nphysical causes can produce the most diversified effects.\u201d\n\nObviously there is a complete misstatement of the argument here; and\nthe excess of the misstatement appears in the following passage: \u201cThe\naction of physical agents upon organized beings presupposes the very\nexistence of those beings.\u201d Who ever doubted it? \u201cThe simple fact that\nthere has been a period in the history of our earth when none of these\norganized beings as yet existed, and when, nevertheless, the material\nconstitution of our globe and the physical forces acting upon it were\nessentially the same as they are now, shows that these influences are\ninsufficient to call into existence any living being.\u201d[18] Although\nmost readers will demur to the statement that because the material\nconstitution of our globe was \u201cessentially the same\u201d before and after\nanimal life appeared, therefore there could have been no special\nconditions determining the appearance of Life, the hypothesis of\nEvolution entirely rejects the notion of organic forms having been\ndiversified by diversities in the few physical conditions commonly\nunderstood as representing the Medium. Mr. Darwin has the incomparable\nmerit of having enlarged our conception of the conditions of existence\nso as to embrace _all_ the factors which conduce to the result. In\nhis luminous principle of the Struggle for Existence, and the Natural\nSelection which such a struggle determines, we have the key to most of\nthe problems presented by the diversities of organisms; and the Law of\nAdaptation, rightly conceived, furnishes the key to all organic change.\n\n58. In consequence of the defective precision with which the phrase\n\u201cMedium,\u201d or its usual equivalent \u201cphysical conditions,\u201d is employed,\nseveral biological errors pass undetected. Haeckel[19] calls attention\nto the common mistake of supposing the organism to be passive under the\ninfluence of external conditions, whereas every action, be it of light\nor heat, of water or food, necessarily calls forth a corresponding\nreaction, which manifests itself in a modification of the nutritive\nprocess. He points out the obverse of this error in the current notion\nthat Habit is solely due to the spontaneous action of the organism,\nin opposition to the influence of external agency,--as if every\naction were not the response to a stimulus. Corresponding with the\nfluctuations in the Medium there must necessarily be fluctuations of\nAdaptation, and I think we may safely assume that it is only when these\nfluctuations cease that the Adaptation becomes Habit. This is the\ninterpretation of the phrase \u201cHabit is _second_ Nature,\u201d and is very\ndifferent from the common interpretation which attributes it to the use\nor disuse of organs; as if use or disuse were a spontaneous uncaused\nactivity.\n\n59. The organism, simple or complex, is, we have already seen, built\nup from materials originally derived from the External Medium, but\nproximately from the Internal Medium. This statement, however, requires\nsome qualification, especially in view of the hypothesis that organized\nsubstance was originally created such as we now find it, and not\nevolved from inorganic materials. Whether this hypothesis be adopted,\nor rejected, we have the fact that the immense majority of organisms\n_now_ existing--if not all--are products of pre-existing organisms;\nand therefore organized matter is now mainly, if not solely, formed by\norganized matter.\n\nWe take, therefore, as our point of departure, the protoplasm; this\nis the first of the three terms of the vital synthesis: Structure,\nAliment, and Instrument. The evolution of this is proximately\ndependent on the _pabulum_ afforded it in the Internal Medium, which\nis the true nutrient material, and to which what is usually called\n_food_ stands in an external relation: for between the reception of\nfood and its assimilation by the organite, there is an indispensable\nintermediary stage, through which matter passes from the unorganized\nto the organized state. This intermediate is now recognized in plants\nas in animals. The old belief that plants were nourished _directly_\nfrom the soil and atmosphere can no longer be sustained. The process\nof Nutrition is alike in both: in both the materials drawn from the\nExternal Medium are formed into proximate principles and organic\nsubstances. It is daily becoming more and more probable that the\ninorganic materials, water and oxygen, so freely entering into the\norganism, never pass directly from the External Medium to the tissues,\nbut have to pass through the Internal Medium where they are changed,\nso that the water is no longer free, but exists in a fixed state\nwhich has no analogue out of the living substance. Only a part of\nthe water can be pressed out mechanically; the rest--that which is\nalready incorporated with the other elements--can only be got rid\nof in a vacuum and at a high temperature. Oxygen, also, comports\nitself differently in the tissue; as is proved by the fact that its\nphysiological absorption is markedly different from any chemical\noxidation in a dead or decomposing tissue.[20] Be this as it may, we\nknow that organic substances have to be unbuilt and rebuilt in the\norganism; that the albumen of our food never passes directly into\nthe albumen of our tissues; any more than the milk drunk by a nursing\nmother will pass into her breasts, and increase her supply, except by\nnourishing her.\n\n60. In the First Series of these Problems the term Bioplasm was\nemployed to designate this organized part of the Internal Medium. I\nwas led to adopt it as a corresponding term to that of Psychoplasm,\nby which I wished to designate the _sentient_ material of the\npsychological medium. There can be little doubt that the term Bioplasm\nwas an unconscious reproduction of the title of Dr. Beale\u2019s work,\nwhich I must have seen advertised. I withdraw it now that I have read\nDr. Beale\u2019s work, and see that the signification he attaches to the\nterm is almost identical with Protoplasm. In lieu thereof, the term\nPlasmode (from _plasma_, anything formed, and _odos_, a pathway) may\nbe substituted: it represents the _nutrient_ material on its way to\nform Protoplasm, which is _formative_ material; while the materials\n_formed_ may be termed Organites and Products: the organite being\nthe cell or cell-derivative (fibre, tube); the products being the\ngaseous liquid and solid derivatives of vital processes, which are\n_secretions_ when they form intercellular substance or return into the\nplasmode and re-enter the vital circle; _excretions_ when they are\nrejected, as incapable of further assimilation. The liver-cell will\nfurnish an example of each kind of product. The bile, though containing\nprinciples serviceable in the chemical transformations, is for the\nmost part excreted; but besides bile, the liver-cell produces starchy\nand saccharine principles which are true secretions, and re-enter the\nplasmode.\n\n61. The organite is thus composed of sap, substance, and product;\nthe organism, of plasmode, tissue, and product. A glance at the\nvegetable-cell shows it to be constituted by the primordial utricle,\nor protoplasm, the outermost layer of which is condensed into a\nmembrane, or cell-wall, and the cavity thus enclosed is filled with\nsap. The cell-wall grows as the protoplasm grows, and the protoplasm\ndraws its material from the plasmode. A glance at the blood, the great\nreservoir of the river of life, shows us plasmode in the serum, and\norganites in the corpuscles; the one distinguished by sodic salts,\nthe other by potassic salts. The plasmode, or serum, is in a constant\nchange of composition and decomposition, giving up to the various\ntissue-organites and intercellular plasmodes the requisite materials,\nand receiving from organites and plasmodes the products of their\nchanges. The serum is fed from the food _and_ the tissues; and it feeds\nthe several plasmodes which bathe the several tissues. Passing into the\ncapillaries, it becomes transformed as it passes through their walls\ninto the intercellular spaces, saturating the acid products of the\ncell-activities with its alkalies, and furnishing the protoplasms with\ntheir needed materials.\n\n62. It will be understood that, although in appearance these stages\nare sharply defined, in reality they are insensible. But from the\nanalytical point of view we may regard Nutrition as the office\nof the plasmode, and Evolution as the office of the protoplasm.\nAlthough evolution or genesis of form depends on assimilation, it is\nnot a necessary consequence: the plasmode or the protoplasm might\npreserve such perfect equality in the waste and repair, such complete\nequilibrium, as not to undergo any development. The ova, for example,\nwhich exist in the ovaries at birth are not all subsequently developed;\nand if with modern embryologists we conclude that there is no\nreplacement of these by proliferation we shall in them have examples of\norganites remaining unchanged through a period of fifty years.[21] But\nsuch an equilibrium is perhaps only possible in complete inactivity.\n\n63. Again, although the office of the plasmode is primarily that of\nforming protoplasm, I think there is evidence to suggest that it not\nonly does this, but that some of it is used in the direct development\nof energy, especially heat and electricity. The various forms of starch\nand sugar taken in with the food or formed in the liver, certainly do\nnot as such enter into protoplasm. The same with alcohol.\n\n64. It is perhaps in forgetfulness of the artificial nature of\nanalytical distinctions that controversies rage respecting what are\ncalled intercellular substances and cell-walls. Now that the wall\nis no longer regarded as an essential constituent of the cell, but\nas a secondary formation, two opinions are maintained: first, that\nit is merely a concentration of the external layer of protoplasm;\nsecondly, that it is a product of secretion from the protoplasm.\nBoth positions may be correct. Certainly in some cases there is no\nother appreciable difference between wall and protoplasm than that\nof a greater consistence; whereas in many other cases there exists a\ndecided difference in their chemical reactions, showing a difference\nof composition. Taking both orders of fact, we may conclude that the\ncell-wall is sometimes part of the organite, and sometimes product: a\nblood-cell and a cartilage-cell may be cited as examples of each. And\nthis argument applies to the intercellular substance also.\n\n65. The terms plasmode and protoplasm are general, and include many\nspecies. There are different plasmodes for the different tissues,\nso that we find phosphates of soda in the blood-serum, phosphates\nof potash in the nerve-plasma, phosphates of magnesia in the\nmuscle-plasma, and phosphates of lime in the bone-plasma; having\nseverally to form the specifically different protoplasms of these\ntissues. Observe, moreover, the gradations of these in respect of their\nphysical state: the blood being the most liquid, the nerve a degree\nmore solid, the muscle still more solid, and the bone almost entirely\nsolid; and since solubility of material is a necessary condition of\nthe chemical changes, we can understand how the blood, the nerve, the\nmuscle, and the bone represent degrees of vital activity: the greater\nthe instability of organized substance, the more active its molecular\nrenovation. Many serious errors result from overlooking the specific\ndifferences of protoplasms; among them may be mentioned that very\ncommon one of asserting that the ovum of a man is not distinguishable\nfrom the ovum of any other mammal, nor the ovum of a mammal from that\nof a reptile; nay, we sometimes see it stated that the protoplasm from\nwhich a mammal may be developed is the same as that which is the germ\nof an oak. So long as this simply asserts that we have at present no\nmeans of distinguishing them by any chemical or physical tests, there\ncan be no objection raised; but it is a serious misconception, which\nany embryological investigation ought to rectify, to suppose that the\novum is not specific from the first.\n\n66. Between the organites and their plasmodes there is the necessary\nrelation, which corresponds with the relation between organisms and\ntheir mediums. Once formed, the organites are arranged side by side,\nor end on end, into textures or tissues, and these are grouped into\norgans, every organ being constituted by a collection of tissues, as\nevery apparatus is by a collection of organs, and the organism by the\nfederation of all the parts. We have more than once insisted on the\nnecessity of synthetic interpretation to complete the indications of\nanalysis: which means that no account of vital phenomena is _real_\nunless it takes in all the co-operant factors, both those of the\norganism and the medium. Neglect of this canon vitiates Dr. Beale\u2019s\notherwise remarkable labors.\n\n\nTHE HYPOTHESIS OF GERMINAL MATTER.\n\n67. It may help to elucidate certain important points if I here examine\nthe hypothesis which Dr. Beale has worked out with such patient skill,\nbut with what seem to me such unphysiological results. He deserves, I\nthink, more applause than has been awarded to him, not only for the\nadmirable patience with which he has pursued the idea, but also for\nthe striking definiteness of the idea itself--always a great advantage\nin an hypothesis, since it gives precision to research. If biologists\nhave paid but little attention to it, this is no doubt due to the\ntheoretical, still more than to the observational contradictions it\npresents. Histologists dispute his facts, or his interpretations;\nwhile other biologists do not see their way in the application of\nhis hypothesis. Respecting all disputed points of observation I\nshall be silent, for I have myself made no systematic researches in\nthis direction, such as would entitle me to form an estimate of the\nevidence. But my dissent from the hypothesis is founded on biological\nprinciples so fundamental that I should be willing to take my stand\nentirely on the facts he himself puts forward.[22]\n\n68. The hypothesis is that nothing in the organism has any claim\nto vitality except the minute masses of protoplasm (by him called\nbioplasm), which in the egg represent, he thinks, about the\none-thousandth part of the whole mass, the rest being lifeless matter,\nnamely, pabulum, and formed material. This bioplasm is the _germinal\nmatter_ out of which, by a _process of dying_, arise the tissues and\nhumors constituting the _formed material_--these, with the pabulum\nwhich feeds the germinal matter, being all dead material. The germinal\nmatter itself, though living, only lives because there is temporarily\nassociated with it that Vital Force of which we have already spoken (\u00a7\n14). In virtue of this association, a particle of matter not exceeding\nthe one hundred-thousandth of an inch in diameter is said to be alive;\nand, presumably, to contain within it all those manifold powers which\nthe term Life condenses. The pabulum brought under the influence of\nthis Vital Force is transformed into germinal matter which, escaping\nfrom this mysterious influence, _dies into tissue_. Muscle-fibres and\nnerve-fibres are thus not living parts, nor are their actions vital. So\nthat, to be consistent, we must not speak of the organism as living,\nbut as a dead structure _produced_ by the Vital Force, and _set in\naction_ by the aid of scattered bits of germinal matter. He has not, I\nthink, stated whether each of these bioplasms has its own Vital Force,\nso that the organism is the theatre of millions of Vital Forces; or\nwhether it is one Vital Force which animates the whole organic world of\nplants and animals. But nothing can be less equivocal than his position\nrespecting the lifelessness of every part of the organism except the\ngerminal matter.\n\n69. The germinal matter may be selected as the primary stage of the\nformed material, the initial point of growth, and thus stand for the\npre-eminently distinctive centre of Nutrition; but were we to limit all\nNutrition to the germinal matter, as defined by Dr. Beale, and deny\nthe co-operation of all the formed material, we should still not be\njustified in restricting Life to simple Nutrition. We cannot exclude\nsuch phenomena as those of Sensation and Motion, nor can we assign\nthese to the germinal matter.[23] To suppose this, would be equivalent\nto saying that the steam which issues from a teakettle is capable of\nthe actions of a locomotive engine. The steam from the kettle is like\nthe steam from the boiler, it has molecular energy, and by this will\nco-operate in the production of mechanical work, if the mechanism be\nadjusted to it. The molecular energy of the protoplasm in muscular\nfibre may be indispensable to the movements of the muscles, but these,\nand not the protoplasmic movements alone, are muscular contractions. An\nhypothesis, therefore, which is obliged to declare that muscle-fibre\nand nerve-fibre are not living, even when active in the organism,\nseems to me defective at its base. If we view these apart from the\norganism, they may, like all the other formed materials, be regarded\nas dead; and no one doubts that epidermis, nail, horn, hair, and bone\nare dead in this sense, that they cannot live independently, and do not\nreproduce themselves. But so long as even these form constituents of\nthe living organism, they also are _living_ (\u00a7 42).[24] It is only by a\nmisconception of the analytical artifice that so simple a truth could\nhave been missed.\n\n70. But this misconception meets us at many a turn. The Vitalist\nhypothesis of an extra-organic agent of course refuses to regard Life\nas the expression of all the co-operant conditions; and even opponents\nof that hypothesis often fall into the same error of principle, when\nthey attempt to explain Life by localizing it in the cells; which is\nsimply a morphological substitution for the once popular doctrine that\nonly the vascular parts were organized, and every part destitute of\nblood-vessels was dead. This idea seemed supported by the facts of the\nmost highly vascular parts being the most vital, and of a parallelism\nexisting between the vital activity of those organs which when injected\nseemed almost entirely composed of blood-vessels, as the liver and\nbrain, and those which showed scarcely a trace of vessels, as cartilage\nand bone; it seemed supported also by the appearance of blood-vessels\nin all new formations, and by the idea of the blood as the nutrient\nfluid. Then came the cell-doctrine, and the belief that the cell was\nthe really ultimate morphological element--which may be true--and that\n\u201chere alone there is any manifestation of life to be found, so that\nwe must not transfer the seat of vital action anywhere beyond the\ncell,\u201d[25]--which is very questionable.\n\n71. We have already seen that the cell is an anatomical element, or\norganite; the organism is but an aggregate of organites _and_ their\nplasmodes. But Biology, which deals with the organism as a whole, and\nwith functions which are the resultants of all the vital properties,\nmust not be restricted to any single factor, however important.\nIt would assuredly be deemed absurd to say that diamond rings and\nlead-pencils were the same, because the diamond and the plumbago,\nwhich are the specific elements of each, are both the same chemical\nelement,--carbon. The substance is really different in diamond and\nplumbago, is different in properties, and is, in rings and pencils,\nunited with different substances into objects having very different\nproperties. Whatever analysis may discover as to the identities of\norganic structures, we cannot explain a single vital phenomenon\nwithout taking into account the three terms, Structure, Aliment,\nand Instrument; and whenever a cell is said to be the seat of vital\naction, these three terms must be implied. In Dr. Beale\u2019s hypothesis\nthe restriction is carried to its extreme; not content with the cell,\nhe withdraws vital action from the cell as a whole, assigning it to\nthe protoplasm and nucleus--cell-contents and cell-wall being, in his\nview, dead. If it be true that the protoplasm is alone concerned in\nNutrition, yet Nutrition is not Life. Occupied mainly with formative\nprocesses, it leaves other indispensable processes to other parts. He\ninstances the removal of all the tissues during the metamorphoses of\ninsects:--\u201cnew organs and textures are laid down afresh and developed\n_ab initio_, instead of being built up upon those first formed.\u201d But to\nshow how he restricts the idea of Life, he adds: \u201cSuch complete change,\nhowever, necessitates a state of existence during which _action_ or\n_function remains in complete abeyance_.\u201d[26]\n\nThe muscles and nerves which are instrumental in this functional life\nare said to be dead. It is true that the muscle-fibre does not develop\nfresh fibres. But it is equally true that the protoplasm of muscle does\nnot alone execute _muscular_ contraction. Each has its special office.\nHence I reject the idea that formed material is dead. He further says\n\u201cformed material may _be_ changed, it cannot _change_ itself.\u201d The\nantithesis is doubly inexact: 1\u00b0, nothing changes itself, but only\nyields to pressure, or reacts on being stimulated; and 2\u00b0, all the\nevidence at hand is against the notion that the formed material is\nnot the seat of incessant molecular change; it is wasted and repaired\nmolecule by molecule. K\u00f6lliker properly protests against the growing\ntendency of histologists to deify protoplasm, and to make it the sole\nseat of vital changes, the cell-wall and cell-products having also, he\nsays, their physiological importance. It is manifestly erroneous to\ndeny vital changes to the red blood-corpuscles on the ground of their\nno longer containing germinal matter.[27]\n\n72. The analytical view may separate certain parts as active, and\nother parts as passive, and thus regard the cells as the seats of\nvital activity, the intercellular substance as merely accessory and\ninstrumental; but the real or synthetical view must recognize both\nparts as equally indispensable, equally vital. Take cartilage, for\ninstance, with its enormous preponderance of intercellular substance\n(formed material), and consider how absolutely impossible any of its\nuses would be were it reduced to the germinal matter of its corpuscles!\nAnd so of all the tissues.\n\n73. If formed material is not to be excluded from the living parts of\nthe organism, neither is the plasmode, out of which the germinal matter\narises, since here we have the nutritive changes in their highest\nactivity; and because the property of Nutrition is here most active,\nthe other property of Development is in abeyance. Dr. Beale holds that\npabulum necessarily becomes germinal matter; but when we come to treat\nof Nutrition it will appear that this is not more true than that Food\nnecessarily becomes Tissue: some of it does; but much of it is used up\nfor heat and other purposes.\n\n74. What is true and important in the distinction between germinal\nmatter and formed material is, that from the former onwards there is a\ngradual process of devitalization, the older parts of every organite\nand tissue approaching more and more to the state of inorganic matter.\nBut to show how vain is the attempt to restrict Vitality to any one\nout of a complex of co-operant factors, we might set up a chemical\nhypothesis to the effect that Vitality depends on phosphates, and\nwith it explain the phenomena quite as well as with the hypothesis of\ngerminal matter. For not only is it found that the productive quality\nof a soil depends on its richness in phosphates, but, as Lehmann has\nshown, wherever cells and fibres make their appearance phosphates\nare found, even in the lowest organisms, which, however, contain but\nlittle. Phosphates abound in seeds and ova, in muscles and ganglia,\nand are deficient in the woody parts of plants and the elastic fibres\nof animals. The infant absorbs phosphates in large quantities and\nexcretes them in small quantities. Nervous activity is accompanied\nby the consumption of a third more phosphorus than accompanies\nmuscular activity. Phosphates are among the most energetic of organic\nstimulants. But who would endow the phosphates with Vitality, on the\nground of their indispensable presence in all vital processes?\n\n75. Life, as we saw, is the expression of the whole organism. Many of\nthe parts are incapable of manifesting any vital phenomena except in\nconnection with all the rest; and of those parts which may be separated\nfrom the organism and continue to manifest some vital phenomena, none\nare capable of manifesting all. When the connexus of the parts is\ndestroyed the organism is dead. Long after that cessation which we call\nDeath, there are still evidences of Vitality in some of the parts:\nthe heart will continue to beat, the glands will secrete, the hair\nwill grow, the temperature will still be above that of the surrounding\nmedium, the muscles will be excitable; these vital properties are\nthe activities of organized substances, and so long as the state of\norganization is preserved they are preserved; but the Life, which\nis the synthesis of all the vital properties, vanishes with the\ndestruction of that synthesis.\n\n76. May we not generalize this, and say that every special form of\nexistence, organic or inorganic, is determined by the synthesis of its\nelements? Atoms are grouped into molecules, molecules into masses,\nmasses into systems. Out of the textureless germinal membrane and\nthe yolk, with no additions from without except oxygen and heat,\nare developed all the textures and organs of the chick; and this\nchick weighs no more than the egg out of which it was evolved. The\ndevelopment has been a succession of syntheses--epigenesis upon\nepigenesis. We may, if we please, regard each organite, as it appears,\nliving its separate life, and each tissue its separate life; but we\nmust not confound under the same symbol modes of existence so widely\ndifferent as the activities of an organite, and the activities of an\norganism constituted by millions of organites.\n\n77. If therefore we cannot restrict Life to the processes of Nutrition,\nDr. Beale\u2019s hypothesis, whatever value it may have as explaining\nhistogenesis, is quite unacceptable. Neither Vital Force nor Bioplasm\ncovers the whole ground. For the former there is no better evidence\nthan our ignorance of the real synthesis; for the latter the evidence\nis positive in its nature, but its interpretation is questionable. Dr.\nBeale selects as the germinal matter those portions of tissue which\nare susceptible of being deeply stained by the carmine solution, the\nformed material being only stained in a faint degree; the nucleus\nand nucleolus are the portions of germinal matter which are most\ndeeply stained; and hence he concludes that the older the matter the\nfainter will be its coloration. There is no dispute as to the value\nof the staining process, invented by Gerlach, for the discrimination\nof chemically different parts of a tissue; and Dr. Beale has made\nexcellent use of it in his researches.[28] But I altogether dispute\nthe conclusion that the staining process reveals the parts which are\nexclusively vital; and for this reason: it depends solely on the acid\nreaction of those parts; and we cannot divorce the acid from the\nalkaline agencies, both being indispensable. Nay, it has been proved\nthat in the _living animal_ no organized substance can be stained. Lord\nGodolphin Osborne first discovered, in 1856, that the protoplasm of\ngrowing wheat was susceptible of coloration;[29] but Gerlach, in 1858,\nfound that this never took place in the _animal_ during life. He kept\ntadpoles and intestinal worms for weeks in colored fluids, without a\nsingle spot becoming stained; although no sooner did these animals die\nthan the staining began. Nor even when he injected the colored fluids\nunder the skin and into the stomach, was the slightest coloration\nproduced.[30]\n\nTo Gerlach\u2019s testimony may be added that of Stein, who, in his\nmagnificent work on _Infusoria_, says that not only has no foreign\nsubstance ever been found in the protoplasm of the _Opalina_, but\nin the _Acineta_, and all the embryos of the higher Infusoria known\nto him, he has been unable to color the living substance.[31] This\nresistance of the living protoplasm is surely a serious objection\nto the hypothesis that only those parts of the dead organism which\nare stained were the truly vital parts. Ranke sums up the results\nof his experiments thus: \u201cThey all show that the living cell resists\nthe imbibition of every substance which it cannot assimilate. It is\nprecisely the impossibility of staining the cell that proves this\nconclusively, since every particle of carmine absorbed would have\nrevealed its presence.\u201d\n\nIt is not to be supposed that Dr. Beale was unacquainted with Gerlach\u2019s\nexperiments. He has at any rate so far qualified the statement of his\nhypothesis as to admit that it is only after death that the germinal\nmatter is stained. \u201cThe living matter\u201d (he says, _How to Work with the\nMicroscope_, p. 107) \u201cpossesses an acid reaction, or to speak more\ncorrectly, an acid reaction is always developed immediately after its\ndeath.\u201d Now, since this acid reaction only presents itself after death,\nand it is this which is revealed by the carmine, we have no right to\nconclude that the carmine singles out the vital parts. Every one knows\nthat the living muscle and nerve, when in repose, present an alkaline\nor faintly neutral reaction, and after excitation this is changed into\nan acid reaction, which increases with the exhaustion of the tissue. In\nstrict logic, therefore--if we could logically apply such a test--it\nis the unstained parts that ought to be called vital. But, in truth,\nalkalinity and acidity are equally indispensable.\n\n78. The main object of my bringing this question forward was to\nillustrate the danger of being misled by analysis: a danger we shall\nsee to be very serious in psychological inquiries. The aid derived from\nanalysis need never be undervalued; all that we have to bear in mind is\nthat it is only a logical artifice, and that our real explanation must\nalways be synthetic. Because of the tendency to rely on analysis there\nhas been an imperfect discrimination of the profound difference between\n\n\nORGANISMS AND MACHINES;\n\nand while on the one hand the legitimate striving of the biologist\nto display the mechanism of organic actions has been denounced by a\ncertain school as Materialism and a hateful attempt to \u201crob Life of\nits mystery,\u201d there has been on the other hand a misconception of this\nmechanism, as if its dependent actions were of the nature of machines,\nthat is to say, as if organized mechanisms were strictly comparable\nwith machines constructed of inorganic parts. No doubt the laws of\nMechanics are the same in both, for these are abstract laws which take\nno account of concrete differences. But when elaborate parallels are\ndrawn up between steam-engines and animal organisms, the coal consumed\nin the one likened to the food in the other, and the force evolved in\nthe combustion in both being the same, there is a complete obliteration\nof all that specially distinguishes vital activity.\n\n79. Between an organism and a machine there is the superficial\nresemblance that both have a complex structure, and are constructed of\ndifferent and dependent parts. But underneath this resemblance there\nis a radical diversity.[32] The arrangement of parts in the organism\nis more than a _juxtaposition_, it is a _solidarity_, arising from\nthe fact of their being all differentiations from a common substance\nwhich is a special combination of the three classes of proximate\nprinciples. Thus they are not parts which have been _put together_, but\nwhich have been _evolved_, each out of a pre-existing part, and each\nco-operating in the very existence of the other. The machine is made\nof independent and primarily unrelated parts; its integrity depends\non the continued preservation of the substance of each part; waste\nis here destruction. The organism is constituted by interdependent\nand primarily related parts; its integrity depends on the continued\ndestruction and renovation of their substance; waste is a condition of\nvitality. The actions of the machine are _sub_ordinated; the actions\nof an organism are _co_-ordinated. The lever moves a wheel, and the\nwheel in moving liberates a spring, each transmitting a communicated\nimpulse, but otherwise each acts independently--no slight modification\nin the structure or movement of the wheel will modify the structure or\nthe movements of the lever, no alteration in the tension of the spring\nwill affect the structure of the wheel. But in the organism all are\nparts of one sympathetic whole; each reacts on each; each is altered\nby the other. Not a nerve is stimulated, nor a muscle moved, but the\nentire organism is affected. A condensation here is the cause of a\ngreater imbibition there. The injection of salt or sugar under the skin\nof the frog\u2019s leg will produce cataract in its eye. The activity of\na secreting cell in the ovary, or liver, alters the condition of the\nbrain; the activity of the brain will check the secretion of a gland,\nor relax the sphincters of the bladder. When we observe the growth of\nhorns, or the appearance of the beard, concomitant with the secretion\nof spermatic cells--and especially when we observe with these a\nsurprising change in the physical and moral capabilities and tendencies\nof the organism--we understand how the remotest parts of this mechanism\nare bound together by one subtle yet all-powerful tie. Nothing of\nthis is visible in a machine. In a machine the material is so far of\nsecondary importance that it may be replaced by materials of various\nkinds: a pulley may be worked with a hempen cord, a silken cord, or an\niron chain; a wheel may be wood, iron, copper, brass, or steel; the\nactions will in each case be similar. Not so the organic mechanism:\nthe slightest variation, either in composition or intimate structure,\nwill affect, and may frustrate the organic activity. It is only in the\nskeleton that the specific character of the materials may be changed;\nand here only in the substitution of one phosphate for another in the\nsolid masonry.[33]\n\n80. Another marked characteristic of the organism is that it has a\nconnexus of actions, the simultaneous effect of a continuous evolution,\nappearing in stages and ages. And in the animal organism there is a\n_consensus_ as well as a _connexus_, through which there is evolution\nof Mind; and in the Social Organism an evolution of Civilization.\nThis consensus forms an intermediate stage through which the animal\nactions are sensitive as well as nutritive, and the nutritive are\nregulated by the sensitive. It is obvious that nothing like this is to\nbe found in a machine; and we conclude, therefore, that any view of the\norganism which regards its mechanism without taking in these cardinal\ncharacteristics must be radically defective. We no more deny the\nexistence of mechanical phenomena in denying that the organism is like\na machine, than we deny the existence of chemical phenomena in denying\nthat Vitality is chemical.\n\n\n\n\nCHAPTER IV.\n\nTHE PROPERTIES AND FUNCTIONS.\n\n\n81. The terms Property and Function are not always used with desirable\nprecision. There is, however, a marked distinction between the property\nwhich characterizes a tissue in whatever organ the tissue may be found,\nand the function which is exhibited by an organ composed of several\ntissues. We ought never to speak of a function unless we imply the\nexistence of a correlative organ; and it is therefore incorrect to\nspeak of the function of Nutrition, since _all_ the tissues nourish\nthemselves; but we may speak of certain organs as special instruments\nin facilitating Nutrition. Thus also with respiration, usually, but not\naccurately, spoken of as the function of the lungs; the lungs being\nsimply the most effective of the instruments by which the interchange\nof gases (which also takes place in every tissue) is facilitated. If\nby Respiration we mean Breathing, then, indeed, Respiration is the\nfunction of the lungs; if we mean the absorption of oxygen and the\nexhalation of carbonic acid, Respiration is a general property of\nvital tissue. A fragment of muscle removed from the body respires, so\nlong as its organization is intact; but it does not _breathe_--it has\nno accessory instruments, nor does it need them. The co-operation of\nnerve centres, diaphragm, ribs, circulating system, etc., necessary\nin the complex organism to bring the due amount of oxygen to the\ntissues, and convey away the carbonic acid, is here needless. In\nthe ascending animal series we find this necessity growing with the\ncomplexity of the organism. The whole skin respires in the amphibia,\nand to some extent in man also: a frog will live for ten or fourteen\ndays after extirpation of its lungs, the skin respiring sufficiently\nto keep up a feeble vitality. But the skin does not suffice; and, very\nearly, certain portions are specialized into organs (at first in the\nshape of external gills, and finally as internal lungs), for the more\nenergetic, because more specialized, performance of this office. In the\nsimpler organisms the blood is easily reached by the air; therefore no\ninstrument is needed. In primitive societies the transport of goods is\neffected by men and women carrying them; in civilized societies by the\naid of horses and camels, and wagons drawn by oxen; till finally these\nare insufficient, and railways are created, whose power of transport\ntranscends the earlier methods, as the breathing of a mammal transcends\nthe respiration of a mollusc. Breathing is the special function of an\norgan--the lungs (or more strictly, the thoracic apparatus)--as Railway\nTransport is a special social function. Although each of the tissues\nforming this organ can, and does, exhale carbonic acid and absorb\noxygen--and each of the railway servants can, and does, transport\nobjects to and from the locomotive--yet the main work is thrown upon\nthe special apparatus.\n\n82. What is meant by properties of tissue and functions of organs\nmay be thus illustrated. Let us suppose ourselves investigating the\nstructure of a ship. We find it composed of various _materials_--wood,\niron, copper, hemp, canvas, etc.; and these under various\n_configurations_ are formed into particular parts serving particular\npurposes, such as deck, masts, anchor, windlass, chains, ropes, sails,\netc. In all these parts the materials preserve their properties; and\nwherever wood or iron may be placed, whatever purpose the part may\nserve, the properties of wood and iron are unaffected; and it is\nthrough a combination of these properties that the part is effective;\nwhile through the connection of one part with another the purpose\nbecomes realized. The purposes to which masts, ropes, or sails are\nsubservient may be called their functions; and these of course only\nexist, _as such_, in the ship. It is the same with the organism. We\nfind it composed of various Tissues, and these are combined into\nvarious Organs or Instruments.[34] The properties of Tissues remain\nthe same, no matter into what Organs they may be combined; they\npreserve and exert their physical, chemical, and vital properties,\nas wood and iron preserve their properties. Each Tissue has its\ncharacteristic quality; and the Organ which is constructed out of a\ncombination of several Tissues, more or less modified, is effective\nsolely in virtue of these properties,[35] while the Function of that\norgan comes into play through its combination with other organs. For\nexample, muscular tissue has a vital property which is characteristic\nof it, Contractility; and muscles are organs constituted by this\ntissue and several others;[36] such organs have the general function\nof Contraction, but whether this shall be specially manifested in\nthe beating of the heart, the winking of the eyelid, the movement\nof the chest, or the varied movements of the limbs, will depend on\nthe _anatomical connections_. The reader unfamiliar with Biology is\nrequested to pay very particular attention to this point; he will find\nmany obscurities dissipated if he once lays hold of the \u201cprincipal\nconnections.\u201d\n\n82_a_. Although Bichat\u2019s conception was of great value, it was\nnot sufficiently disengaged from the metaphysical mode of viewing\nbiological phenomena. Both he and his disciples will be found treating\nProperties as entities, and invoking them as _causes_ of the phenomena\ninstead of recognizing them simply as abstract _expressions_ of the\nphenomena. Readers of my First Series will remember how often I have\nhad occasion to point out this common error: men having baptized\nobserved facts with a comprehensive name, forget the process of\nbaptism, and suppose the name to represent a mysterious agency. The\nfact that gases combine is expressed in the term affinity; and then\nAffinity is understood to be the cause of the combinations. The fact\nthat bodies tend towards each other is called their gravitation, and\nGravitation is then said to cause the tendency. The doctrine of vital\nproperties has been thus misunderstood. While no one imagines that\nhe can operate on affinity otherwise than by operating on the known\nconditions under which gases combine, many a biologist and physician\nspeaks as if he could operate on the Irritability of a tissue, or the\nCo-ordination of muscles, by direct action on these abstractions.\n\nLet it be therefore once for all expressly stated that by the property\nof a tissue is simply meant the _constant mode of reaction of that\ntissue under definite conditions_. The property is not a cause,\notherwise than the conditions it expresses are a cause. And these\nconditions are first those of the organized structure itself, and\nsecondly those of the medium in which it lives. Oxygen unites with\nHydrogen to form water, but only under certain pressures; so likewise\nmuscles manifest Contractility on being stimulated (that is their mode\nof reaction), but only under certain degrees of temperature, humidity,\nand a certain chemical composition of the plasmode. The property is\nso truly an expression of the co-operant conditions, that it is found\nto vary with those conditions, and to vanish when they vary beyond a\ncertain limit.\n\nAn attempt has been made to restrict the notion of a property to an\nultimate fact. Whatever is not reducible to known conditions is to\nbe accepted as a property. Combustion, for example, is reducible to\nthe molecular combination of oxygen and some other gas; but this\ncombination itself is not reducible, and it is therefore christened\naffinity. I cannot accept this view. Admitting our inability to say\n_why_ gases combine under certain conditions (and in this sense all\nfacts are inexplicable and ultimate, unless we take the _how_ as\nample explanation of the _why_), I must still say that since affinity\nitself depends on the co-operation of known conditions, it is not less\nexplicable than combustion. But the point is unimportant: what we have\nhere to settle is the meaning of a property of tissue,--and that is the\nmode of reaction which that tissue manifests under constant conditions,\ninternal and external.\n\n83. The evolution of Life is the evolution of special properties and\nfunctions from general properties and functions. The organism rises in\npower as it ramifies into variety. Out of a seemingly structureless\ngerminal membrane, by successive differentiations certain portions\nare set apart for the dominant, or exclusive, performance of certain\nprocesses; just as in the social organism there is a setting apart\nof certain classes of men for the dominant or exclusive performance\nof offices, which by their co-operation constitute Society. The\nsoldier fights, but ceases to build or reap, weave or teach; the\nmason builds; the agriculturist sows and reaps; the priest and\nthinker teach; the statesman governs. In simple societies each\ndoes all, or nearly all; but the social life thus manifested is\nmarkedly inferior to the energetic life of a complex society. So with\norganisms. An am\u0153ba manifests the general properties of Nutrition,\nReproduction, Sensibility, and Movement. But it has no special organs,\nconsequently no special functions. The polype has a certain rudimentary\nspecialization of parts: it has a simple alimentary cavity, and\nprehensile tentacles; and although by these it can seize and digest its\nprey, it can only do so in a limited way--all the manifold varieties\nand power of prehension and digestion observed in more complex\norganisms are impossible with such organs as the polype possesses.\n\n84. Differences of structure and connection necessarily bring about\ncorresponding differences in Function, since Function is the _directed\nenergy_ of the Properties of tissues. One organ will differ from\nanother in structure, as the liver from the pancreas, or the kidney\nfrom the spleen; or one organ may closely resemble another but differ\nfrom it only in _connections_, as a sensory and a motor nerve, or an\nextensor and a flexor muscle. We must therefore always bear both points\nin mind. Every modification, structural or connectional, is translated\nby a corresponding modification in the office. The hand and the foot\nshow this well. The tissues are the same in both, the properties are\nthe same, and both have the same general function of Prehension; but\ntheir morphological differences carry corresponding differences in\ntheir uses.\n\nSuppose we have a galvanic battery, we know that its electric force\nmay be variously applied. Two pieces of charcoal fixed to the ends of\nits conducting wires give us the electric light; replacing the charcoal\nby a telegraphic apparatus we can transmit a message from one continent\nto the other; the wires dipped in a solution effect a chemical\ndecomposition, dipped into a mixture of gases they effect a chemical\ncomposition. In these, and many other applications, the property of the\nbattery is constant; but the functions it subserves have varied with\nthe varying co-operants. So with the properties of tissue.[37] Not only\nhave we to bear in mind the organic connections of the tissues, but\nalso the relation of the organs to their media. Swimming and Walking,\nfor example, are both functions of the locomotive apparatus, but they\nare specially differenced by the media in which the animal moves.\n\n85. The properties of tissues are their peculiar modes of reaction, and\neach tissue has its dominant characteristic, such as the Contractility\nof the muscle, and the Neurility of the nerve. But there has of late\nyears sprung up a misleading conception, partly a consequence of the\ncell-theory, and partly of the almost inevitable tendency of analysis\nto disregard whatever elements it provisionally sets aside; this\nconception is the removal of the property from its _tissue_, and the\nlocalization of it in one of the _organites_--cell or fibre. This has\nbeen conspicuously mischievous in the case of the nerve-cell, which has\nbeen endowed with mysterious powers, and may be said to have usurped\nthe place of nerve-tissue. I shall have to speak of this in the next\nproblem. Here I only warn the student against the common error. The\nproperties of a tissue depend on the structure and composition of\nthat tissue, together with its plasmode and products; they vary as\nthese vary. To select any one element in this complex, and ascribe the\nreaction of the tissue to that, is only permissible as a shorthand\nexpression.\n\n86. What has just been expounded may be condensed in the following\nbiological law:--\n\n    _Identity of tissue everywhere implies identity of property; and\n    similarity of tissue corresponding similarity of property. Identity\n    of organic connection everywhere implies identity of function; and\n    similarity of organic connection similarity of function._\n\n87. This law, first formulated by me in 1859, and then applied to the\ninterpretation of nervous functions, was so little understood that for\nthe most part it met with either decided denial or silent neglect;\nno doubt because of the general disinclination to admit that the\nproperties and functions of the spinal cord could be _similar_ to those\nof the brain, in correspondence with the similarity of their tissues\nand organic connections. Even Professor Vulpian, who adopted it, as\nwell as my principal interpretations, hesitated, and relapsed into the\northodox view in assigning three different properties to one and the\nsame tissue in cord, medulla oblongata, and cerebrum.[38] In the course\nof our inquiries we shall so frequently have to invoke this law that I\nearnestly beg the reader to meditate upon it, and ask himself upon what\nother grounds, save those of structure and connection, the properties\nand functions can possibly rest? If on no other, then similarity in\nstructure and connection by logical necessity involves similarity in\nproperty and function.\n\n\nDOES THE FUNCTION DETERMINE THE ORGAN?\n\n88. Closely connected with this law, which simply formulates the\nself-evident principle that _every action is rigorously determined by\nthe nature of the agent, and the conditions under which the act takes\nplace_, is the surprising question whether functions are dependent\nupon organs, or organs dependent on functions?--a question which\nsometimes takes this shape: Is Life the result of organization, or is\norganization the result of Life?\n\nThe vitalist, who holds that Life is an extra-organic agent, is logical\nin declaring organization to be the consequence of Life;[39] but there\nare many organicists who conclude from certain facts that organs are\ndeveloped by functions, and that organization is a result of Life.\nThere seems, however, to be some equivoque here. I cannot otherwise\nunderstand how Mr. Spencer should have written: \u201cThere is one fact\nimplying that Function must be regarded as taking the precedence of\nStructure. Of the lowest rhizopods which present no distinctions\nof parts, and nevertheless feed and grow and move about, Professor\nHuxley has remarked that they exhibit Life without Organization.\u201d[40]\nThe equivoque here arises from the practice of calling all living\nbodies \u201corganisms,\u201d even those destitute of the differentiations\ncalled organs; but if we substitute the term \u201cliving body\u201d in lieu of\n\u201corganism,\u201d the equivoque will disappear, and Function no longer seem\nto precede Structure. Neither Mr. Spencer nor Mr. Huxley would affirm\nthat Life can be manifested without a living body; and every living\nbody must have a structure of some sort--unless by structure be meant\na special configuration of parts. The properties of a body, whether it\nbe simple or complex in structure, result from the properties of its\ncomponents; and the vital phenomena vary with these varying components.\nThe substance of a Rhizopod is indeed simple as compared with that of\nhigher organisms, but is complex as compared with anorganisms; and\ncorresponding with this simplicity of structure there is simplicity of\nvital function.[41]\n\n89. The _properties_ of steam are exhibited by the kettle on the fire,\nno less than by the gigantic engine which animates a manufactory;\nbut the _uses_ of steam (the functions of the engine) vary with the\nvarying structure, and the applications of that structure to other\nstructures. Precisely analogous is the case of the organ and its\nfunction, in relation to the living substance of which it is a peculiar\nmodification. Vital actions are manifested by a lump of protoplasm; but\nthese actions are as sharply demarcated from the actions of more highly\norganized animals, as the phenomena of a steam-engine are from those of\na teakettle.\n\n90. Mr. Spencer has nowhere defined what he means by Structure, nor\ngiven a definition of Organ, and this neglect makes it difficult\nrightly to appreciate his view. But whether we take structure to\nsignify the _substance_ of the living body, or the _differentiations_\nof that substance into separate tissues and organs, in either case\nthe actions (functions) of which this structure is the agent must be\nrigorously determined by it. Mr. Spencer has avowed this in declaring\nthat the \u201cgeneral physiologist may consider functions in their widest\nsense as the correlatives of tissue.\u201d Is this true in the widest sense\nand not true in the narrowest? I am puzzled to find him insisting that\n\u201cfunction from beginning to end is the determining cause of structure.\nNot only is this manifestly true where the modification of structure\narises by reaction from modification of function; but it is also\ntrue where a modification of structure otherwise produced apparently\ninitiates a modification of function.\u201d Such language would be\nconsistent were he a vitalist who believed in a Principle independent\nof Matter which shapes matter into organic forms; but as a positive\nthinker he can scarcely escape the admission that since Function is the\nactivity of the Agent (Function in the widest sense being the action\nof the whole Organism, and in its narrowest sense the action of the\nspecial Organ) there cannot be an _activity preceding the agent_. I\nsuspect that he does not always bear in mind the distinction between\nProperty and Function, and consequently is led into statements at\nvariance with the principles he professes. As far as I understand the\ncourse of his thought, it runs somewhat thus: With the increased use\nof an organ its volume may be increased, its structure altered; this\nalteration will, by reaction, cause alterations in other organs, and\nthus the result of a change in the habitual activities of an animal\nwill be an alteration in the arrangement of its parts.\n\n91. We speak loosely of an organ being developed by increased activity;\nbut this is loose speech, and investigation shows that the organ is not\ndeveloped _by_, but accompanies the increased activity, every increment\nof activity being necessarily preceded by a corresponding increment\nof structure. This is evident _\u00e0 priori_: the force manifested is\ninherent in the structure manifesting it. Thus we ought not to say\n\u201cthe vascular system furnishes good instances of the increased growth\nthat _follows_ increased function\u201d; we ought to say, \u201cthat _permits_\nincreased function.\u201d The muscle having a contractile power represented\nby 10, expends, we will suppose, 7 units of force in its normal\nactivity, and these are replaced by its normal nutrition. If from an\nextra demand upon it 9 units are expended, the muscle becomes fatigued,\nif 10, exhausted, and it will no longer contract, the whole disposable\nsum of its contractility being dissipated. During all these stages the\nstructure of the muscle--or to prevent all equivoque, let us say the\nsubstance of the muscle--has been changing, not indeed in any degree\nappreciable to the eye, but appreciable by the more decisive tests of\nchemical and physiological reactions. Yet inasmuch as in the ordinary\ncourse of things the waste is quickly repaired, the muscle in repose\nonce more regains its original state, once more represents 10 units of\ncontractility. Now let us consider what takes place when extra labor\nis thrown upon the muscle, when exercise causes growth. At the outset\nof a walking tour we may not be able to compass more than twenty miles\na day, at its close we manage thirty. Is it the increased activity\nof the function which has caused this increase of structure? In one\nsense, yes; but let us understand it. Had the increase of activity\nbeen temporary, there would have been only a temporary increase of\nstructure. But when the ordinary expenditure of 7 units rises to 9,\non several successive days, this extra expenditure of tissue has had\nto be met by an extra nutrition--i.\u00a0e. more plasmode has been formed\nand more protoplasm. It is a physiological law, easily explained,\nthat, within due limits, extra waste brings about extra repair: as the\nchannels are widened and multiplied, the _derived_ currents become\nstronger, and the increased flow of nutrition which was temporary\nbecomes permanent, because this increase is no longer dependent on an\nextra stimulus, but on an enlarged channel.[42] When the channels have\nnot become multiplied or enlarged, which must be the case whenever the\nextra stimulus is fluctuating and temporary, the extra expenditure is\nnot followed by increased size of the muscle: the currents resume their\nold directions, no longer being diverted.\n\n92. Let the social organism furnish us with an illustration. At the\npresent moment there is a movement against the retail shopkeepers of\nLondon in favor of Co-operative Stores. The stimulus of getting better\ngoods and cheaper, attracts the flow of custom from its old channels;\nand if this continue a certain time the new arrangements will be so\nthoroughly organized, and will work so easily, that Co-operative Stores\nwill to a great extent supplant the retail shops. But if from any\ncauses the stimulus slackens before this reorganization has passed from\nthe oscillating into the permanent stage--if the goods are not found\nto be superior, or the cheapness not worth the extra trouble--the old\ninfluences (aiding our indolence) which have been long and continuously\nat work, will cause the social organism to resume its old aspect,\nand the co-operative \u201cvarieties\u201d will disappear, or exist beside the\nancient \u201cspecies.\u201d\n\nIn the one case as in the other a glance at the process is enough\nto detect that the increase in the activity has been preceded by\na corresponding increase in the structure. The muscle has not been\nenlarged _by_ extra activity, but _with_ it. The co-operative action\nhas grown with each additional co-operator. Looking at the cases from\nafar we may justly say that development has been due to function; but\nlooking to the process we see that each increment of activity was\nnecessarily dependent on an increment of substance. When changes of\nhabit or adaptation are said to produce modifications in structures,\nthis is true in as far as one modification of structure necessarily\nbrings with it correlative modifications, the growth of one part\naffecting the growth of all more or less; but we must remember that\nto render the structure capable of new adaptations corresponding\nmodifications must have been going on. The retail shopkeepers might\nsecurely laugh at the co-operative movement if the respectable families\nwould not or could not become co-operant. When Mr. Spencer urges that\n\u201cnot only may leaf-stalks assume to a great degree the character of\nstems when they have to discharge the functions of stems by supporting\nmany leaves, and very large leaves, but they may assume the characters\nof leaves when they have to undertake the functions of leaves,\u201d I would\nask if he is not reversing the actual process? The stem cannot assume\nthe functions of a leaf until it has first assumed the character of a\nleaf. The assumptions of both must be gradual, and _pari passu_.\n\n93. The hand is an organ, its function is prehension. The performance\nof this function in any of its numerous applications is rigorously\nlimited by the structure of the hand--the bones, muscles, nerves,\ncirculating and absorbent vessels, connective tissue, fat, etc. Fatigue\nthe nerve, and the function will be feebly performed; exhaust it,\nand the function ceases; diminish the action of the heart, tie an\nartery, or vitiate the structure of the blood, and the function will\nbe correspondingly affected; stiffen the tendons, soften the bones,\ndiminish the synovial fluid, or increase the fat--in short, make _any_\nalteration whatever in the structure of the hand, and an alteration\nis necessarily produced in its function. So rigorously is function\ndependent upon structure, that the hand of one man will execute\nactions which are impossible to another. The hand of a baby is said to\nbe the same in structure as the hand of a man; and since the powers\n(functions) of the two are notoriously different, we might rashly\nconclude that here function was dissociated from structure. The case is\nillustrative. In baby and man the structure is similar, not the same;\nthe resemblance is of kind, not of degree; and the function likewise\nvaries with the degree. The penny cannon which delights the child is\nsimilar in structure to the ten-pounder which batters down walls; and\nthough, speaking generally, we may say that the function of both is to\nfire gunpowder for human ends, no one expects the penny cannon to be\nemployed in warfare. In physiology, as in mechanics, the effect varies\nwith the forces involved.\n\nThere can be no doubt that an exaggerated activity will produce a\nmodification in the active organ, for this is only the familiar case of\nincreased growth with increased exercise, and this is the biological\nmeaning in which Function can be said not, indeed, to _create_, but to\n_modify_ an existing Organ. Preceding the activity there must be the\nagent. Every organ although having its special function has also the\nproperties of all the tissues which constitute it. The function is only\nthe synthesis of these properties to which a dominant tissue gives a\nspecial character. The eye, for example, though specially characterized\nby its retinal sensibility to light, is largely endowed with muscles,\nand its movements are essential to Vision. The intestinal canal, again,\nthough specially characterized by its secretions for the decomposition\nof food, has muscles which are essential to Digestion. In many animals,\nespecially vegetable-feeders, there is an exaggeration of the muscular\nactivity in certain parts of the intestinal canal which is only\npossible through a corresponding development of the muscular tissue, so\nthat in some birds, crustaceans, and molluscs we find a gizzard, which\nis wholly without a mucous membrane to secrete fluids, and which aids\nDigestion solely by trituration.\n\n94. Mr. Spencer, as I have already suggested, seems to have been\nled into his view by not keeping distinctly present to his mind the\ndifferences between Properties of tissue and Function, the activity\nof an organ. \u201cThat function takes precedence of structure,\u201d he says,\n\u201cseems implied in the definition of Life. If Life consist of inner\nactions so adjusted as to balance outer actions--if the actions are\nthe _substance_ of Life, while the adjustment constitutes its _form_;\nthen may we not say that the actions formed must come before that which\nforms them--that the continuous change which is the basis of function\nmust come before the structure which brings the function into shape?\u201d\nThe separation of \u201cactions formed\u201d from \u201cthat which forms them\u201d is\ninadmissible. An action cannot come _before_ the agent: it is the\nagent in act. The continuous change, which is the basis of Vitality,\nis a change of molecular arrangements; and the organ which gives a\nspecial _direction_ to the vital activity, e.\u00a0g. which shapes the\nproperty of Contractility into the function of Prehension, this organ\nmust itself be formed before it can manifest this function. It is true\nthat in one sense the organs are formed by, or are differentiated in,\na pre-existent organism; true that the general activity of living\nsubstance must precede the special activity of any organ, as the\nexpansions of steam must precede any steam-engine action; but the\ngeneral activity depends on the general structure; and the special\nactions on the special structures. If by Organization we are to\nunderstand not simply organized substance, but a more or less complex\narrangement of that substance into separate organs, the question is\ntantamount to asking whether the simplest animals and plants have life?\nAnd to ask the question, whether Life precedes organic substance? is\ntantamount to asking whether the convex aspect of a curve precedes\nthe concave! or whether the motions of a body precede the body! To\ndisengage ourselves from the complicated suggestions of such a word as\nLife, let us consider one of the vital phenomena, Contraction. This\nis a phenomenon manifested by simple protoplasm, and by the highly\ndifferentiated form of protoplasm known as muscle. In one sense it\nwould be correct to say that Contractility as a general property of\ntissue precedes Contraction, which is specialized in muscle. But\nit would be absurd to say that _muscular_ contraction preceded the\nexistence of muscle, and formed it. The contractions of the protoplasm\nare not the same as muscular contractions any more than the hand of\na baby is the same as a man\u2019s; the general property which both have\nin common depends on the substance both have in common; the special\nproperty which belongs to the muscle depends on its special structure.\nAn infinite activity of the contractile protoplasm would be incompetent\nto form a muscle, unless it were accompanied by that peculiar change in\nstructure which constitutes muscle. The teakettle might boil forever\nwithout producing a steam-engine or the actions of a steam-engine. That\nwhich is true of one function is true of all functions, and true of\nLife, which is the sum of vital activities.\n\n95. It is this haziness which made Agassiz \u201cregret to observe that\nit has almost become an axiom that identical functions presuppose\nidentical organs. There never was a more incorrect principle leading\nto more injurious consequences.\u201d[43] And elsewhere he argues that\norgans can exist without functions. But this is obviously to pervert\nthe fundamental idea of an organ. \u201cThe teeth of the whale which never\neat through the gums, and the breasts of the males of all classes\nof mammalia,\u201d are cited by him as examples of such organs without\nfunctions; but in the physiological significance of the term these are\nnot organs at all. It is no more to be expected that the breasts of\nthe male should act in lactation, than that the slackened string of a\nviolin should yield musical tones; but the breasts of the male may be\neasily stimulated into yielding milk, and the slackened string of the\nviolin may be tightened so as to yield tone. Even the breasts of the\nfemale do not yield milk except under certain conditions, and in the\nabsence of these are on a par with those of the male.\n\n96. Organized substance has the general properties of Assimilation,\nEvolution, Sensibility, and Contractility; each of the special\ntissues into which organized substance is differentiated manifests a\npredominance of one of these properties. Thus although the embryo-cells\nall manifest contractility, it is only the specialized muscle-cell\nwhich continues throughout its existence to manifest this property,\nand in a dominant form; the muscle-cell also assimilates and develops,\nbut besides having these properties in common with all other cells, it\nhas the special property of contracting with an energy not found in\nthe others. All cells respire; but the blood-cells have this property\nof absorbing oxygen to a degree so far surpassing that of any other\ncell that physiologists have been led to speak of their containing a\npeculiar respiratory substance. In like manner all, or nearly all,\nthe tissues contain _myeline_--which indeed is one of the chief\nconstituents of the yolk of eggs--but only in the white sheath of the\nnerves is it detached and specialized as a tissue.\n\n97. But while Sensibility and Contractility are general properties\nof organized substance, specialized in special tissues; Sensation\nand Contraction are functions of the organs formed by such tissues;\nand these organs are only found in animal organisms. It is a serious\nerror, which we shall hereafter have to insist on, to suppose that\nSensation can be the property of ganglionic cells, or, as it is more\noften stated, the property of the central gray matter. Sensation is\nthe function of the organism; it varies with the varying organ; the\nsensation of Touch not being the same as the sensation of Sight, or of\nSound.\n\n98. We may consider the organism under two aspects--that of Structure\nand that of Function. The latter has two broad divisions corresponding\nwith the vegetal and animal lives; the one is Nutrient, the other\nEfficient. The one prepares and distributes Food, the other distributes\nMotion. Of course this separation is analytical. In reality the two are\ninterblended; and although the neuro-muscular system is developed out\nof the nutritive system, it is no sooner developed than it plays its\npart as Instrument in the preparation and distribution of Aliment.\n\nThis not being a treatise on Physiology, there can be no necessity for\nour here considering the properties and functions in detail. What is\nnecessary to be said on Sensibility and Contractility will find its\nplace in the course of future chapters; for the present we will confine\nourselves to Evolution on account of its psychological, no less than\nits physiological, interest.\n\n\n\n\nCHAPTER V.\n\nEVOLUTION.\n\n\n99. That organized substance has the property of nourishing itself\nby assimilating from its internal medium substances there present in\nan unorganized state, and that this is followed by a development or\ndifferentiation of structure, is familiar to every inquirer.\n\nEvery one who has pursued embryological researches, and in a lesser\ndegree every one who has merely read about them, must have been\nimpressed by this marvel of marvels: an exceedingly minute portion\nof living matter, so simple in aspect that a line will define it,\npasses by successive modifications into an organism so complex that a\ntreatise is needed to describe it; not only do the cells in which the\novum and the spermatozoon originate, pass into a complex organism,\nreproducing the forms and features of the parents, and with these\nthe constitutional peculiarities of the parents (their longevity,\ntheir diseases, their mental dispositions, nay, their very tricks and\nhabits), but they may reproduce the form and features, the dispositions\nand diseases, of a grandfather or great-grandfather, which had lain\ndormant in the father or mother. Consider for an instant what this\nimplies. A microscopic cell of albuminous compounds, wholly without\ntrace of organs, not appreciably distinguishable from millions of other\ncells, does nevertheless contain within it the \u201cpossibilities\u201d of an\norganism so complex and so special as that of a Newton or a Napoleon.\nIf ever there was a case when the famous Aristotelian notion of a\n\u201cpotential existence\u201d seemed justified, assuredly it is this. And\nalthough we can only by a fallacy maintain the oak to be _contained_\nin the acorn, or the animal contained in the ovum, the fallacy is so\nnatural, and indeed so difficult of escape, that there is no ground\nfor surprise when physiologists, on first learning something of\ndevelopment, were found maintaining that the perfect organism existed\nalready in the ovum, having all its lineaments in miniature, and only\ngrowing into visible dimensions through the successive stages of\nevolution.[44] The preformation of the organism seemed an inevitable\ndeduction from the opinions once universal. It led to many strange,\nand some absurd conclusions; among them, to the assertion that the\noriginal germ of every species contained within it all the countless\nindividuals which in process of time might issue from it; and this in\nno metaphysical \u201cpotential\u201d guise, but as actual boxed-up existences\n(_embo\u00eet\u00e9s_); so that Adam and Eve were in the most literal sense\nprogenitors of the whole human race, and contained their progeny\nalready shaped within them, awaiting the great accoucheur, time.\n\n100. This was the celebrated \u201cembo\u00eetement\u201d theory. In spite of obvious\nobjections it gained scientific acceptance, because physiologists could\nnot bring themselves to believe that so marvellous a structure as that\nof a human organism arose by a series of successive modifications, or\nbecause they could not comprehend how it was built up, part by part,\ninto forms so closely resembling the parent-forms. That many and\nplausible reasons pleaded in favor of this opinion is evident in the\nfact that illustrious men like Haller, Bonnet, Vallisneri, Swammerdamm,\nR\u00e9aumur, and Cuvier, were its advocates; and if there is not a sigle\nphysiologist of our day who accepts it, or who finds any peculiar\ndifficulty in following the demonstrations of embryologists, how from\nthe common starting-point of a self-multiplying epithelial cell parts\nso diverse as hairs, nails, hoofs, scales, feathers, crystalline lens,\nand secreting glands may be evolved, or how from the homogeneous\ngerminal membrane the complex organism will arise, there are very\nfew among the scorners of the dead hypothesis who seem capable of\ngeneralizing the principles which have destroyed it, or can conceive\nthat the laws of Evolution apply as rigorously to the animal and\nvegetable _kingdoms_ as to the individual _organisms_. The illustrious\nnames of those who advocated the preformation hypothesis may serve to\ncheck our servile submission to the authorities so loudly proclaimed as\nadvocates of the fixity of species. The more because the two doctrines\nhave a common parentage. The one falls with the other, and no array of\nauthorities can arrest the fall. That the manifold differentiations\nnoticeable in a complex organism should have been evolved from a\nmembrane wholly destitute of differences is a marvel, but a marvel\nwhich Science has made intelligible. Yet the majority of those to\nwhom this has been made intelligible still find an impossibility in\nadmitting that the manifold forms of plant and animal were successively\nevolved from equally simple origins. They relinquish the hypothesis of\npreformation in the one case, and cling to it in the other. Evolution,\ndemonstrable in the individual history, seems preposterous in the\nhistory of the class. And thus is presented the instructive spectacle\nof philosophers laughing at the absurdities of \u201cpreformation,\u201d and\nyet exerting all their logic and rhetoric in defence of \u201ccreative\nfiats\u201d--which is simply the preformation hypothesis \u201cwrit large.\u201d\n\n101. It would not be difficult to show that the doctrine of\nEpigenesis, with which Wolff forever displaced the doctrine of\nPreformation, leads by an inevitable logic to the doctrine of universal\nEvolution; and that we can no more understand the appearance of a\nnew organism which is not the modification of some already existing\norganism, than we can understand the sudden appearance of a new organ\nwhich is not the modification of some existing structure. In the one\ncase as in the other we may disguise the process under such terms as\ncreative fiat and preformation; but these terms are no explanations;\nthey re-state the results, they do not describe the process; whereas\nEpigenesis describes the process as it passes under the eye of science.\n\n102. If any reader of these pages who, from theological or zo\u00f6logical\nsuspicion of the Development Hypothesis, clings to the hypothesis\nof a creative Plan which once for all arranged the organic world in\nTypes that could not change, will ask what rational interpretation can\nbe given to the succession of phases each embryo is forced to pass\nthrough, it may help to give him pause. He will observe that _none_ of\nthese phases have any adaptation to the future state of the animal, but\nare in positive contradiction to it, or are simply purposeless; whereas\nall show stamped on them the unmistakable characters of _ancestral_\nadaptations and the progressions of Organic Evolution. What does the\nfact imply? There is not a single known example of a complex organism\nwhich is not developed out of simpler forms. Before it can attain the\ncomplex structure which distinguishes it, there must be an evolution of\nforms similar to those which distinguish the structures of organisms\nlower in the series. On the hypothesis of a Plan which prearranged\nthe organic world, nothing could be more unworthy of a supreme\nintelligence than this inability to construct an organism at once,\nwithout previously making several tentative efforts, undoing to-day\nwhat was so carefully done yesterday, and _repeating for centuries the\nsame tentatives, and the same corrections, in the same succession_. Do\nnot let us blink this consideration. There is a traditional phrase much\nin vogue among the anthropomorphists, which arose naturally enough from\nthe tendency to take human methods as an explanation of the divine--a\nphrase which becomes a sort of argument--\u201cThe Great Architect.\u201d But\nif we are to admit the human point of view, a glance at the facts of\nembryology must produce very uncomfortable reflections. For what should\nwe say to an architect who was unable, or being able was obstinately\nunwilling, to erect a palace except by first using his materials in the\nshape of a hut, then pulling it down and rebuilding them as a cottage,\nthen adding story to story and room to room, _not_ with any reference\nto the ultimate purposes of the palace, but wholly with reference to\nthe way in which houses were constructed in ancient times? What should\nwe say to the architect who could not form a museum out of bricks\nand mortar, but was forced to begin as if going to build a mansion:\nand after proceeding some way in this direction, altered his plan\ninto a palace, and that again into a museum? Yet this is the sort of\nsuccession on which organisms are constructed. The fact has long been\nfamiliar; how has it been reconciled with Infinite Wisdom? Let the\nfollowing passage answer for a thousand:--\u201cThe embryo is nothing like\nthe miniature of the adult. For a long while the body in its entirety\nand its details presents the strangest of spectacles. Day by day and\nhour by hour the aspect of the scene changes, and this instability is\nexhibited by the most essential parts no less than by the accessory\nparts. One would say that Nature feels her way, and only reaches the\ngoal after many times missing the path,--on dirait que la nature\nt\u00e2tonne et ne conduit son \u0153uvre \u00e0 bon fin qu\u2019apr\u00e8s s\u2019\u00eatre souvent\ntromp\u00e9e.\u201d[45] Writers have no compunction in speaking of Nature feeling\nher way and blundering; but if in lieu of Nature, which may mean\nanything, the Great Architect be substituted, it is probable that the\nrepugnance to using such language of evasion may cause men to revise\ntheir conceptions altogether; they dare not attribute ignorance and\nincompetence to the Creator.\n\n103. Obviously the architectural hypothesis is incompetent to explain\nthe phenomena of organic development. Evolution is the universal\nprocess; not creation of a direct kind. Von Baer, who very properly\ncorrected the exaggerations which had been put forth respecting the\nidentity of the embryonic forms with adult forms lower in the scale,\nwho showed that the mammalian embryo never was a bird, a reptile,\nor a fish, nevertheless emphasized the fact that the mammalian\nembryo passes through all the lower typical forms; so much so that,\nexcept by their size, it is impossible to distinguish the embryos of\nmammal, bird, lizard, or snake. \u201cIn my collection,\u201d he says, \u201cthere\nare two little embryos which I have omitted to label, so that I am\nnow quite incompetent to say to what class they belong. They may be\nlizards, they may be small birds, or very young mammals; so complete\nis the similarity in the mode of formation of the head and trunk.\nThe extremities have not yet made their appearance. But even if they\nexisted in the earliest stage we should learn nothing from them, for\nthe feet of lizards, mammals, and the wings of birds, all arise from\nthe same common form.\u201d He sums up with his formula: \u201cThe special type\nis always evolved from a more general type.\u201d[46]\n\nSuch reminiscences of earlier forms are intelligible on the supposition\nthat originally the later form was a modification of the earlier form,\nand that this modification is repeated; or on the supposition that\nthere was a similarity in the organic conditions, which similarity\nceased at the point where the new form emerged. But on no hypothesis\nof creative Plan are they intelligible. They are useless structures,\nfailing even to subserve a temporary purpose. Sometimes, as Mr. Darwin\nremarks, a trace of the embryonic resemblance lasts till a late age:\n\u201cThus birds of the same genus, and of closely allied genera, often\nresemble each other in their first and second plumage: as we see in\nthe spotted feathers in the thrush group. In the cat tribe most of the\nspecies are striped and spotted in lines; and stripes or spots can\nplainly be distinguished in the whelp of the lion and the puma. We\noccasionally, though rarely, see something of this kind in plants....\nThe points of structure in which the embryos of widely different\nanimals of the same class resemble each other often have no direct\nrelation to their conditions of existence. We cannot, for instance,\nsuppose that in the embryos of the vertebrata the peculiar loop-like\ncourses of the arteries near the bronchial slits are related to similar\nconditions in the young mammal which is nourished in the womb of its\nmother, in the egg of a bird which is hatched in a nest, and in the\nspawn of a frog under water.\u201d\n\n104. It would be easy to multiply examples, but I will content myself\nwith three. The tadpole of the Salamander has gills, and passes his\nexistence in the water; but the _Salamandra atra_, which lives high\nup among the mountains, brings forth its young full-formed. This\nanimal never lives in the water. Yet if we open a gravid female, we\nfind tadpoles inside her with exquisitely feathered gills, and (as I\nhave witnessed) these tadpoles \u201cwhen from the mother\u2019s womb untimely\nripped,\u201d if placed in water, swim about like the tadpoles of water\nnewts. Obviously this aquatic organization has no reference to the\nfuture life of the animal, nor has it any adaptation to its embryonic\ncondition; it has solely reference to ancestral forms, it repeats a\nphase in the development of its progenitors. Again, in the embryo of\nthe naked Nudibranch, we always observe a shell, although the animal\nis without a shell, and there can be no purpose served by the shell in\nembryonic life.[47] Finally, the human embryo has a tail, which is of\ncourse utterly purposeless, and which, although to be explained as a\nresult of organic laws, is on the creative hypothesis only explained as\nan adherence to the general plan of structure--a specimen of pedantic\ntrifling \u201cworthy of no intellect above the pongo\u2019s.\u201d[48]\n\n105. Humanly appreciated, not only is it difficult to justify the\nsuccessive stages of development, the incessant building up of\nstructures immediately to be taken down, but also to explain why\ndevelopment was necessary at all. Why are not plants and animals\nformed at once, as Eve was mythically affirmed to be taken from Adam\u2019s\nrib, and Minerva from Jupiter\u2019s head? The theory of Evolution answers\nthis question very simply; the theory of Creation can only answer\nit by affirming that such was the ordained plan. But the theory of\nEvolution not only gives the simpler and more intelligible answer to\nthis question, it gives an answer to the further question which leaves\nthe theory of Creation no loophole except a sophism--namely, why the\nformation of organisms is constantly being frustrated or perverted?\nAnd, further, it gives an explanation of the law noticed by Milne\nEdwards, that Nature is as economical in her means as she is prodigal\nin her variation of them: \u201cOn dirait qu\u2019avant de recourir \u00e0 des\nressources nouvelles elle a voulu \u00e9puiser, en quelque sorte, chacun\ndes proc\u00e9d\u00e9s qu\u2019elle avait mis en jeu.\u201d[49] The applause bestowed on\nNature for being economical is a curious transference to Nature of\nhuman necessities. Why, with a whole universe at her disposal, should\nNature be economical? Why must she always be working in the same\ngroove, and using but a few out of the many substances at her command?\nEconomy is a virtue only in the poor. If Nature, in organic evolutions,\nis restricted to a very few substances, and a very few modes of\ncombination, always creating new forms by modification of the old, and\napparently incapable of creating an organism at once, this must imply\nan inherent necessity which is very unlike the free choice that can\nrender economy a merit.\n\n106. There may indeed be raised an objection to the Development\nHypothesis on the ground that if the complex forms were all developed\nfrom the simpler forms, we ought to trace the identities through all\ntheir stages. If the fish developed into the reptile, the reptile\ninto the bird, and the bird into the mammal (which I, for one, think\nquestionable), we ought to find, it is urged, evidence of this passage.\nAnd at one time it was asserted that the evidence existed; but this\nhas been disproved, and on the disproof the opponents of Evolution\ntake their stand. Although I cannot feel much confidence in the idea\nof such a passage from Type to Type, and although the passage, if ever\nit occurred, must have occurred at so remote a period as to leave\nno evidence more positive than inference, I cannot but think the\nteaching of Embryology far more favorable to it than to our opponents.\nSupposing, for the sake of argument, that the passage did take place,\nought we to find the embryonic stages accurately reproducing the\npermanent forms of lower types? Von Baer thinks we ought; and lesser\nmen may follow him without reproach. But it seems to me that he starts\nfrom an inadmissible assumption, namely, that the development must\nnecessarily be in a straight line rather than in a multiplicity of\ndivergent lines. \u201cWhen we find the embryonic condition,\u201d he says,\n\u201cdiffering from the adult, we ought to find a corresponding condition\nsomewhere in the lower animals.\u201d[50] Not necessarily. We know that\nthe mental development of a civilized man passes through the stages\nwhich the race passed through in the course of its long history, and\nthe psychology of the child reproduces the psychology of the savage.\nBut as this development takes place under conditions in many respects\ndifferent, and as certain phases are hurried over, we do not expect\nto find a complete parallel. It is enough if we can trace general\nresemblances. Von Baer adds, \u201cThat certain correspondences should occur\nbetween the embryonic states of some animals and the adult states of\nothers seems inevitable and of no significance(?). They could not fail,\nsince the embryos lie within the animal sphere, and the variations\nof which the animal body is capable are determined for each type by\nthe internal connection and mutual reaction of its organs, so that\nparticular repetitions are inevitable.\u201d A profound remark, to which I\nshall hereafter have occasion to return, but its bearing on the present\nquestion is inconclusive. The fact that the embryonic stages of the\nhigher animals resemble in general characters the permanent stages\nof the lower animals, and very closely resemble the embryonic stages\nof those animals, is all that the Development Hypothesis requires.\nNor is its value lessened by the fact that many of the details and\nintermediate stages seem passed over in the development of the higher\nforms, for the recapitulation can only be of outlines, not of details;\nsince there are differences in the forms, there must be differences in\ntheir histories.\n\n107. In the preceding observations the object has simply been to show\nthat the phenomena to be explained can be rationally conceived as\nresulting from gradual Evolution, whereas they cannot be so rationally\ninterpreted on any other hypothesis. And here it may be needful to say\na word respecting Epigenesis.\n\nThe Preformation hypothesis, which regarded every organism as a simple\neduct and not the product of a germ, was called by its advocates an\nevolution hypothesis--meaning that the adult form was an outgrowth of\nthe germ, the miniature magnified. Wolff, who replaced that conception\nby a truer one, called his, by contrast, Epigenesis, meaning that\nthere was not simply _out_-growth but _new_ growth. \u201cThe various\nparts,\u201d he says, \u201carise one _after_ the other, so that always one is\nsecreted from (_excernirt_), or deposited (_deponirt_) on the other;\nand then it is either a free and independent part, or is only fixed\nto that which gave it existence, or else is contained within it. So\nthat _every part is the effect of a pre-existing part, and in turn\nthe cause of a succeeding part_.\u201d[51] The last sentence expresses\nthe conception of Epigenesis which embryologists now adopt; and\nhaving said this, we may admit that Wolff, in combating the error\nof preformation, replacing it with the truer notion of gradual and\nsuccessive formation, was occasionally open to the criticism made\nby Von Baer, that he missed the true sense of Evolution, since the\nnew parts are not _added on_ to the old parts as new formations,\nbut _evolved from_ them as transformations. \u201cThe word Evolution,\ntherefore, seems to me more descriptive of the process than Epigenesis.\nIt is true that the organism is not preformed, but the course of its\ndevelopment is precisely the course which its parents formerly passed\nthrough. Thus it is the Invisible--the course of development--which is\npredetermined.\u201d[52] When the word Epigenesis is used, therefore, the\nreader will understand it to signify that necessary succession which\ndetermines the existence of new forms. Just as the formation of chalk\nis not the indifferent product of any combination of its elements,\ncarbon, oxygen, and calcium, but is the product of only one series of\ncombinations, an evolution through necessary successions, the carbon\nuniting with oxygen to form carbonic acid, and this combining with the\noxide of calcium to form chalk, so likewise the formation of a muscle,\na bone, a limb, or a joint has its successive stages, each of which\nis necessary, none of which can be transposed. The formation of bone\nis peculiarly instructive, because the large proportion of inorganic\nmatter in its substance, and seemingly deposited in the organic tissue,\nwould lead one to suppose that it was almost an accidental formation,\nwhich might take place anywhere; yet although what is called\nconnective tissue will ossify under certain conditions, true bone is\nthe product of a very peculiar modification, which almost always needs\nto be preceded by cartilage. That the formation of bone has its special\nhistory may be seen in the fact that it is the last to appear in the\nanimal series, many highly organized fishes being without it, and all\nthe other systems appearing before it in the development of the embryo.\nThus although the mother\u2019s blood furnishes all the requisite material,\nthe f\u0153tus is incapable of assimilating this material and of forming\nbone, until its own development has reached a certain stage. Moreover,\nwhen ossification does begin, it generally begins in the skull (in\nman in the clavicle); and the only approach to an internal skeleton\nin the Invertebrates is the so-called skull of the Cephalopoda.\nNot only is bone a late development, but cartilage is also; and\nalthough it is an error to maintain that the Invertebrates are wholly\ndestitute of cartilage, its occasional presence having been fully\nproved by Clapar\u00e8de and Gegenbaur, the rarity of its presence is very\nsignificant. The animals which can form shells of chalk and chitine are\nyet incapable of forming even an approach to bone.\n\n108. Epigenesis depends on the laws of succession, which may be likened\nto the laws of crystallization, if we bear in mind the essential\ndifferences between a crystal and an organism, the latter retaining\nits individuality through an incessant molecular change, the former\nonly by the exclusion of all change. When a crystalline solution\ntakes shape, it will always take a definite shape, which represents\nwhat may be called the _direction_ of its forces, the polarity of\nits constituent molecules. In like manner, when an organic plasmode\ntakes shape--crystallizes, so to speak--it always assumes a specific\nshape dependent on the polarity of its molecules. Crystallographers\nhave determined the several forms possible to crystals; histologists\nhave recorded the several forms of Organites, Tissues, and Organs.\nOwing to the greater variety in elementary composition, there is in\norganic substance a more various polar distribution than in crystals;\nnevertheless, there are sharply defined limits never overstepped, and\nthese constitute what may be called the specific forms of Organites,\nTissues, Organs, Organisms. An epithelial cell, for example, may be\nciliated or columnar, a muscle-fibre striated or non-striated, a\nnerve-fibre naked or enveloped in a sheath, but the kind is always\nsharply defined. An intestinal tube may be a uniform canal, or a canal\ndifferentiated into several unlike compartments, with several unlike\nglandular appendages. A spinal column may be a uniform solid axis, or\na highly diversified segmented axis. A limb may be an arm, or a leg, a\nwing, or a paddle. In every case the anatomist recognizes a specific\ntype. He assigns the uniformities to the uniformity of the substance\nthus variously shaped, under a history which has been similar; the\ndiversities he assigns to the various conditions under which the\nprocesses of growth have been determined. He never expects a muscular\ntissue to develop into a skeleton, a nervous tissue into a gland,\nan osseous tissue into a sensory organ. He never expects a tail to\nbecome a hand or a foot, though he sees it in monkeys and marsupials\nserving the offices of prehension and locomotion. He never expects\nto find fingers growing anywhere except from metacarpal bones, or an\narm developed from a skull. The well-known generalization of Geoffroy\nSt. Hilaire that an organ is more easily annihilated than transposed,\npoints to the fundamental law of Epigenesis. In the same direction\npoint all the facts of growth. Out of a formless germinal membrane we\nsee an immense variety of forms evolved; and out of a common nutritive\nfluid this variety of organs is sustained, repaired, replaced; and\nthis not indifferently, not casually, but according to rigorous laws\nof succession; that which precedes determining that which succeeds\nas inevitably as youth precedes maturity, and maturity decay. The\nnourishment of various organs from plasmodes derived from a common\nfluid, each selecting from that fluid only those molecules that are\nlike its own, rejecting all the rest, is very similar to the formation\nof various crystals in a solution of different salts, each salt\nseparating from the solution only those molecules that are like itself.\nReil long ago called attention to this analogy. He observed that if\nin a solution of nitre and sulphate of soda a crystal of nitre be\ndropped, all the dissolved nitre crystallizes, the sulphate remaining\nin solution; whereas on reversing the experiment, a crystal of sulphate\nof soda is found to crystallize all the dissolved sulphate, leaving the\nnitre undisturbed. In like manner muscle selects from the blood its own\nmaterials which are there in solution, rejecting those which the nerve\nwill select.\n\n109. Nay, so definite is the course of growth, that when a limb or part\nof a limb is cut off from a crab or salamander, a new limb or new part\nis reproduced in the old spot, exactly like the one removed. Bonnet\nstartled the world by the announcement that the _Na\u00efs_, a worm common\nin ponds, spontaneously divided itself into two worms; and that when he\ncut it into several pieces, each piece reproduced head and tail, and\ngrew into a perfect worm. This had been accepted by all naturalists\nwithout demur, until Dr. Williams, in his \u201cReport on British Annelida,\n1851,\u201d declared it to be a fable. In 1858, under the impulse of Dr.\nWilliams\u2019s very emphatic denial, I repeated experiments similar to\nthose of Bonnet, with similar results. I cut two worms in half, and\nthrew away the head-bearing segments, placing the others in two\nseparate vessels, with nothing but water and a little mud, which was\nfirst carefully inspected to see that no worm lay concealed therein. In\na few days the heads were completely reformed, and I had the pleasure\nof watching them during their reconstruction. When the worms were quite\nperfect, I again cut away their heads, and again saw these reformed.\nThis was repeated, till I had seen four heads reproduced; after which\nthe worms succumbed.\n\n110. The question naturally arises, Why does the nutritive fluid\nfurnish only material which is formed into a part like the old one,\ninstead of reproducing another part, or one having a somewhat different\nstructure? The answer to this question is the key to the chief problem\nof organic life. That a limb _in situ_ should replace its molecular\nwaste by molecules derived from the blood, seems intelligible enough\n(because we are familiar with it), and may be likened to the formation\nof crystals in a solution; but how is it that the limb _which is not\nin existence_ can assimilate materials from the blood? How is it that\nthe blood, which elsewhere in the organism will form other parts,\nhere will only form this particular part? There is, probably, no one\nwho has turned his attention to these subjects who has not paused to\nconsider this mystery. The most accredited answer at present before the\nworld is one so metaphysiological that I should pass it by, were it\nnot intimately allied with that conception of Species, which it is the\nobject of these pages to root out. It is this:\n\n111. The organism is determined by its Type, or, as the Germans say,\nits Idea. All its parts take shape according to this ruling plan;\nconsequently, when any part is removed, it is reproduced according to\nthe Idea of the whole of which it forms a part. Milne Edwards, in a\nvery interesting and suggestive work, concludes his survey of organic\nphenomena in these words: \u201cDans l\u2019organisme tout semble calcul\u00e9 en\nvue d\u2019un r\u00e9sultat d\u00e9termin\u00e9, et l\u2019harmonie des parties ne r\u00e9sulte\npas de l\u2019influence qu\u2019elles peuvent exercer les unes sur les autres,\nmais de leur co-ordination sous l\u2019empire d\u2019une puissance commune,\nd\u2019un plan pr\u00e9con\u00e7u, d\u2019une force pr\u00e9-existante.\u201d[53] This is eminently\nmetaphysiological. It refuses to acknowledge the operation of immanent\nproperties, refuses to admit that the harmony of a complex structure\nresults from the mutual relations of its parts, and seeks _outside_\nthe organism for some mysterious force, some plan, not otherwise\nspecified, which regulates and shapes the parts. Von Baer, in his great\nwork, has a section entitled, \u201cThe nature of the animal determines\nits development\u201d; and he thus explains himself: \u201cAlthough every stage\nin development is only made possible by the pre-existing condition\n[which is another mode of expressing Epigenesis], nevertheless the\nentire development is ruled and guided by the Nature of the animal\nwhich is about to be (von der gesammten Wesenheit des Thieres welches\nwerden soll), and it is not the momentary condition which alone\nand absolutely determines the future, but more general and higher\nrelations.\u201d[54] One must always be slow in rejecting the thoughts\nof a master, and feel sure that one sees the source of the error\nbefore regarding it as an error; but in the present case I think the\npositive biologist will be at no loss to assign Von Baer\u2019s error to\nits metaphysical origin. Without pausing here to accumulate examples\nboth of anomalies and slighter deviations which are demonstrably due\nto the \u201cmomentary conditions\u201d that preceded them, let us simply note\nthe logical inconsistency of a position which, while assuming that\n_every separate stage_ in development is the necessary sequence of its\npredecessor, declares the _whole of the stages_ independent of such\nrelations! Such a position is indeed reconcilable on the assumption\nthat animal forms are moulded \u201clike clay in the hands of the potter.\u201d\nBut this is a theological dogma, which leads to very preposterous and\nimpious conclusions; and whether it leads to these conclusions or to\nothers, positive Biology declines theological explanations altogether.\nVon Baer, although he held the doctrine of Epigenesis, coupled it,\nas many others have done, with metaphysical doctrines to which it is\nradically opposed. He believed in Types as realities; he was therefore\nconsistent in saying, \u201cIt is not the Matter and its arrangements which\ndetermine the product, but the nature of the parent form--the Idea,\naccording to the new school.\u201d How are we to understand this Idea? If\nit mean an independent Entity, an agency external to the organism, we\nrefuse to acknowledge its existence. If it mean only an _a posteriori_\nabstraction expressing the totality of the conditions, then, indeed,\nwe acknowledge that it determines the animal form; but this is only an\nabbreviated way of expressing the law of Evolution, by which each stage\ndetermines its successor. The Type does not _dominate_ the conditions,\nit _emerges_ from them; the animal organism is not cast in a mould, but\nthe imaginary mould is the form which the polarities of the organic\nsubstance assume. It would seem very absurd to suppose that crystals\nassumed their definite shapes (when the liquid which held their\nmolecules in solution is evaporated) under the determining impulse\nof phantom-crystals, or Ideas; yet it has not been thought absurd to\nassume phantom forms of organisms.\n\n112. The conception of Type as a determining influence arises from\nthat fallacy of taking a resultant for a principle, which has played\nso conspicuous a part in the history of philosophy. Like many others\nof its class it exhibits an interesting evolution from the crude\nmetaphysical to the subtle metaphysical point of view, which at last\ninsensibly blends into the positive point of view. At first the Type or\nIdea was regarded as an objective reality, external to the organism it\nwas supposed to rule. Then this notion was replaced by an approach to\nthe more rational interpretation, the idea was made an internal not an\nexternal force, and was incorporated with the material elements of the\norganism, which were said to \u201cendeavor\u201d to arrange themselves according\nto the Type. Thus Treviranus declares that the seed \u201cdreams of the\nfuture flower\u201d; and \u201cHenle, when he affirms that hair and nails grow in\nvirtue of the Idea, is forced to add that the parts endeavor to arrange\nthemselves according to this Idea.\u201d[55] Even Lotze, who has argued\nso victoriously against the vitalists, and has made it clear that an\norganism is a vital mechanism, cannot relinquish this conception of\nlegislative Ideas, though he significantly adds, \u201cthese have no power\nin themselves, but only in as far as they are grounded in mechanical\nconditions.\u201d Why then superfluously add them to the conditions? If\nevery part of a watch, in virtue of the properties inherent in its\nsubstance, and of the mutual reactions of these and other parts,\nhas a mechanical value, and if the sum of all these parts is the\ntime-indicating mechanism, do we add to our knowledge of the watch, and\nour means of repairing or improving it, by assuming that the parts have\nover and above their physical properties the metaphysical \u201ctendency\u201d\nor \u201cdesire\u201d to arrange themselves into this specific form? When we\nsee that an organism is constructed of various parts, each of which\nhas its own properties inalienable from its structure, and its uses\ndependent on its relation to other parts, do we gain any larger insight\nby crediting these parts with desires or \u201cdreams\u201d of a future result\nwhich their union will effect? That which is true in this conception of\nlegislative Ideas is that when the parts come together there is mutual\nreaction, and the resultant of the whole is something very unlike\nthe mere addition of the items, just as water is very unlike oxygen\nor hydrogen; further, the connexus of the whole impresses a peculiar\ndirection on the development of the parts, and the law of Epigenesis\nnecessitates a serial development, which may easily be interpreted as\ndue to a preordained plan.\n\n113. In a word, this conception of Type only adds a new name to the\nold difficulty, adding mist to darkness. The law of Epigenesis,\nwhich is simply the expression of the material process determined by\nthe polarity of molecules, explains as much of the phenomena as is\nexplicable. A lost limb is replaced by the very processes, and through\nthe same progressive stages as those which originally produced it. We\nhave a demonstration of its not being reformed according to any Idea\nor Type which exists apart from the immanent properties of the organic\nmolecules, in the fact that it is not reformed at once, but by gradual\nevolution; the mass of cells at the stump are cells of embryonic\ncharacter, cells such as those which originally \u201ccrystallized\u201d into\nmuscles, nerves, vessels, and integument, and each cell passes through\nall its ordinary stages of development. It is to be remembered that so\nintimately dependent is the result on the determining conditions, that\nany external influence which disturbs the normal course of development\nwill either produce an anomaly, or frustrate the formation of a new\nlimb altogether. One of my tritons bit off the leg of his female;[56]\nthe leg which replaced it was much malformed, and curled over the back\nso as to be useless; was this according to the Idea? I cut it off, and\nexamined it; all the bones were present, but the humerus was twisted,\nand of small size. In a few weeks a new leg was developed, and this\nleg was normal. If the Idea, as a ruling power, determined the growth\nof this third leg, what determined the second, which was malformed?\nAre we to suppose that in normal growth the Idea prevails, in abnormal\nthe conditions? That it is the polarity of the molecules which at\neach moment determines the group those molecules will assume, is well\nseen in the experiment of Lavalle mentioned by Bronn.[57] He showed\nthat if when an octohedral crystal is forming, an angle be cut away,\nso as to produce an artificial surface, a similar surface is produced\nspontaneously on the corresponding angle, whereas all the other angles\nare sharply defined. \u201cValentin,\u201d says Mr. Darwin, \u201cinjured the caudal\nextremity of an embryo, and three days afterwards it produced rudiments\nof a double pelvis, and of double hind limbs. Hunter and others have\nobserved lizards with their tails reproduced and doubled. When Bonnet\ndivided longitudinally the foot of the salamander, several additional\ndigits were occasionally formed.\u201d[58] Where is the evidence of the Idea\nin these cases?\n\n114. I repeat, the reproduction of lost limbs is due to a process which\nis in all essential respects the same as that which originally produced\nthem; the genesis of one group of cells is the necessary condition\nfor the genesis of its successor, nor can this order be transposed.\nBut--and the point is very important--it is not every part that can be\nreproduced, nor is it every animal that has reproductive powers. The\nworm, or the mollusk, seems capable of reproducing every part; the crab\nwill reproduce its claws, but not its head or tail; the perfect insect\nof the higher orders will reproduce no part (indeed the amputation of\nits antennae only is fatal), the salamander will reproduce its leg,\nthe frog not. In human beings a muscle is said never to be reproduced;\nbut this is not the case in the rare examples of supplementary fingers\nand toes, which have been known to grow again after amputation.\nThe explanation of this difference in the reproductive powers of\ndifferent animals is usually assigned to the degree in which their\norganisms retain the embryonic condition; and this explanation is made\nplausible by the fact that the animals which when adult have no power\nof replacing lost limbs, have the power when in the larval state. But\nalthough this may in some cases be the true explanation, there are\nmany in which it fails, as will be acknowledged after a survey of the\nextremely various organisms at widely different parts of the animal\nseries which possess the reproductive power. Even animals in the same\nclass, and at the same stage of development, differ in this respect.\nI do not attach much importance to the fact that all my experiments\non marine annelids failed to furnish evidence of their power of\nreproducing lost segments; because it is difficult to keep them under\nconditions similar to those in which they live. But it is significant\nthat, among the hundreds which have passed under my observation, not\none should have been found with a head-segment in the process of\ndevelopment, replacing one that had been destroyed; and this is all the\nmore remarkable from the great tenacity of life which the mutilated\nsegments manifest. Quatrefages had observed portions of a worm, after\ngangrene had destroyed its head and several segments, move about in the\nwater and avoid the light![59]\n\n115. A final argument to show that the reproduction is not determined\nby any ruling Idea, but by the organic conditions and the necessary\nstages of evolution, is seen in the reappearance of a tumor or cancer\nafter it has been removed. We find the new tissue appear with all the\ncharacters of the normal tissue of the gland, then rapidly assume one\nby one the characters of the diseased tissue which had been removed;\nand there as on is, that the regeneration of the tissue is accompanied\nby the same abnormal conditions which formerly gave rise to the tumor:\nthe directions of \u201ccrystallization\u201d are similar because the conditions\nare similar. In every case of growth or regrowth the conditions being\nthe same, the result must be the same.\n\n116. It seems a truism to insist that similarity in the results must be\ndue to similarity in the conditions; yet it is one which many theorists\ndisregard; and especially do we need to bear it in mind when arguing\nabout Species. I will here only touch on the suggestive topic of the\nanalogies observed not simply among animals at the extreme ends of the\nscale, but also between animals and plants where the idea of a direct\nkinship is out of the question.\n\nMy very imperfect zo\u00f6logical knowledge will not allow me to adduce a\nlong array of instances, but such an array will assuredly occur to\nevery well-stored mind. It is enough to point to the many analogies\nof Function, more especially in the reproductive processes--to the\nexistence of burrowers, waders, flyers, swimmers in various classes--to\nthe existence of predatory mammals, predatory birds, predatory\nreptiles, predatory insects by the side of herbivorous congeners,--to\nthe nest-building and incubating fishes; and in the matter of Structure\nthe analogies are even more illustrative when we consider the widely\ndiffused spicula, set\u00e6, spines, hooks, tentacles, beaks, feathery\nforms, nettling-organs, poison-sacs, luminous organs, etc.; because\nthese have the obvious impress of being due to a community of substance\nunder similar conditions rather than to a community of kinship. The\nbeak of the tadpole, the cephalopod, the male salmon, and the bird,\nare no doubt in many respects unlike; but there is a significant\nlikeness among them, which constitutes a true analogy. I think there\nis such an analogy between the air-bladder of fishes and the tracheal\nrudiment which is found in the gnat-larva (_Corethra plumicornis_).[60]\nVery remarkable also is the resemblance of the _avicularium_, or\n\u201cbird\u2019s-head process,\u201d on the polyzoon known popularly as the Corkscrew\nCoralline (_Bugula avicularia_), which presents us in miniature\nwith a vulture\u2019s head--two mandibles, one fixed, the other moved by\nmuscles visible within the head. No one can watch this organ snapping\nincessantly, without being reminded of a vulture, yet no one would\nsuppose for a moment that the resemblance has anything to do with\nkinship.\n\n117. Such cases are commonly robbed of their due significance by being\ndismissed as coincidences. But what determines the coincidence? If we\nassume, as we are justified in assuming, that the _possible directions_\nof Organic Combination, and the resultant forms, are limited, there\nmust inevitably occur such coincident lines: the hooks on a Climbing\nPlant will resemble the hooks on a Crustacean or the claws of a Bird,\nas the one form in which under similar external forces the more solid\nbut not massive portions of the integument tend to develop. I am too\nill acquainted with the anatomy of plants to say how the hooks so\ncommon among them arise; but from examination of the Blackberry, and\ncomparison of its thorns with the hooks and spines of the Crustacea,\nI am led to infer that in each case the mode of development is\nidentical--namely, the secretion of chitine from the cellular matrix of\nthe integument.\n\nAnother mode of evading the real significance of such resemblances\nis to call them analogies, not homologies. There is an advantage in\nhaving two such terms, but we ought to be very clear as to their\nmeaning and their point of separation. Analogy is used to designate\nsimilarity in Function with dissimilarity in Structure. The wing\nof an insect, the wing of a bird, and the wing of a bat are called\nanalogous, but not homologous, because their anatomical structure is\ndifferent: they are not constructed out of similar anatomical parts.\nThe fore-leg of a mammal, the wing of a bird, or the paddle of a\nwhale, are called homologous, because in spite of their diverse uses\nthey are constructed out of corresponding anatomical parts. To the\nanatomist such distinctions are eminently serviceable. But they have\nled to some misconceptions, because they are connected with a profound\nmisconception of the relation between Function and Organ. Embryology\nteaches that the wing of the bird and the paddle of the whale are\ndeveloped out of corresponding parts, and that these are not like the\nparts from which the wing of an insect or the flying-fish will be\ndeveloped; nevertheless, the most cursory inspection reveals that the\nwing of a bird and the paddle of a whale are very unlike in structure\nno less than in function, and that their diversities in function\ncorrespond with their diversities in structure; whereas the wing of the\ninsect, of the bird, and of the bat, are in certain characters very\nsimilar, and correspondingly there are similarities in their function.\nIt is, however, obvious that the resemblance in function is strictly\nlimited to the resemblance in anatomical structure; only in loose\nordinary speech can the flight of an insect, a bird, or a bat be said\nto be \u201cthe same\u201d: it is different in each--the weight to be moved, the\nrapidity of the movement, the precision of the movements, and their\nendurance, all differ.\n\n\nNATURAL SELECTION AND ORGANIC AFFINITY.\n\n118. It is impossible to treat of Evolution without taking notice\nof that luminous hypothesis by which Mr. Darwin has revolutionized\nZo\u00f6logy. There are two points needful to be clearly apprehended before\nthe question is entered upon. The first point relates to the lax use\nof the phrase \u201cconditions,\u201d sometimes more instructively replaced by\n\u201cconditions of existence.\u201d Inasmuch as Life is only possible under\ndefinite relations of the organism and its medium, the \u201cconditions of\nexistence\u201d will be those physical, chemical, and physiological changes,\nwhich _in_ the organism, and _out_ of it, _co-operate_ to produce the\nresult. There are myriads of changes in the external medium which have\nno corresponding changes in the organism, not being in any direct\nrelation to it (see \u00a7 54). These, not being co-operant conditions,\nmust be left out of the account; they are not conditions of existence\nfor the organism, and therefore the organism does not vary with their\nvariations. On the other hand, what seem very slight changes in the\nmedium are often responded to by important changes in the vital\nchemistry, and consequently in the structure of the organism. Now the\nnature of the organism at the time being, that is to say, its structure\nand the physico-chemical state of its tissues and plasmodes, is the\nmain _condition_ of this response; the same external agent will be\npowerful, or powerless, over slightly different organisms, or over the\nsame organism at different times. Usually, and for convenience, when\nbiologists speak of conditions, they only refer to external changes.\nThis usage has been the source of no little confusion in discussing\nthe Development Hypothesis. Mr. Darwin, however, while following the\nestablished usage, is careful in several places to declare that of the\ntwo factors in Variation--the nature of the organism and the nature of\nthe conditions--the former is by far the more important.\n\n118_a_. A still greater modification of terms must now be made. Instead\nof confining the \u201cstruggle for existence\u201d to the competition of rivals\nand the antagonism of foes, we must extend it to the competition and\nantagonism of tissues and organs. The existence of an organism is not\nonly dependent on the external existence of others, and is the outcome\nof a struggle; but also on the internal conditions which co-operate in\nthe formation of its structure, this structure being the outcome of a\nstruggle. The organism is this _particular_ organism, differing from\nothers, because of the particular conditions which have co-operated.\nThe primary and fundamental struggle must be that of the organic\nforces at work in creating a structure capable of pushing its way\namid external forces. The organism must find a footing in the world,\nbefore it can compete with rivals, and defend itself against foes.\nOwing to the power of reproduction, every organism has a potential\nindefiniteness of multiplication; that potential indefiniteness is,\nhowever, in reality restricted by the supply of food, and by the\ncompetition of rivals for that supply. The multiplication of any one\nspecies is thus kept down by the presence of rivals and foes: a balance\nis reached, which permits of the restricted quantities of various\nspecies. This balance is the result of a struggle.\n\nNow let me call attention to a similar process in the formation of the\norganism itself. Every organite, and every tissue, has a potential\ngrowth of indefinite extent, but its real growth is rigorously limited\nby the competition and antagonism of the others, each of which has\nits potential indefiniteness, and its real limits. Something, in the\nfood assimilated, slightly alters the part which assimilates it. This\nchange may be the origin of other changes in the part itself, or in\nneighboring parts, stimulating or arresting the vital processes. A\nmodification of structure results. Or there may be no new substance\nassimilated, but external forces may call a part into increased\nactivity--which means increased waste and repair; and this increase\nhere is the cause of a corresponding decrease somewhere else. Whatever\nthe nature of the change, it finds its place amid a complex of changes,\nand its results are compounded with theirs. When organites and tissues\nare said to have a potential indefiniteness of growth, there is\nassumed a potential indefiniteness in the pabulum supplied: _if_ the\npabulum were supplied, and _if_ there were no antagonism thwarting its\nassimilation, growth would of course continue without pause, or end;\nbut in reality this cannot be so. For, take the blood as the vehicle\nof the pabulum--not only is its quantity limited, and partly limited\nby the very action of the tissues it feeds, but even in any given\nquantity there is a limit to its composition--it will only take up a\nlimited quantity of salts, iron, albumen, etc.; no matter how abundant\nthese may be in the food. So again with the plasmodes of the various\ntissues--they have each their definite capacities of assimilation. What\nhas already been stated respecting chemical affinity (\u00a7 20) is equally\napplicable to organic affinity; as the presence of fused iron in the\ncrucible partially obstructs the combination of sulphur and lead, so\nthe presence of connective tissue partially obstructs the combination\nof muscle protoplasm with its pabulum.\n\n118 _b_. Owing to the action and reaction of blood and plasmode, of\ntissues on tissues, and organs on organs, and their mutual limitations,\nthe growth of each organism has a limit, and the growth of each organ\nhas a limit. Beyond this limit, no extra supply of food will increase\nthe size of the organism; no increase of activity will increase the\norgan. \u201cMan cannot add a cubit to his stature.\u201d The blacksmith\u2019s arm\nwill not grow larger by twenty years of daily exercise, after it has\nonce attained a certain size. Increase of activity caused it to enlarge\nup to this limit; but no increase of activity will cause it to pass\nthis limit. Why? Because here a balance of the co-operating formative\nforces has been reached. Larger muscles, or more muscle-fibres, demand\narteries of larger calibre, and these a heart of larger size; with\nthe increase of muscle would come increase of connective tissue; and\nthis tissue would not only compete with the muscle for pabulum, but\nby mechanical pressure would diminish the flow of that pabulum. And\nwhy would connective tissue increase? Because, in the first place,\nthere is a formative association between the two, so that owing to a\nlaw, not yet understood, the one always accompanies the other; and,\nin the second place, there is a functional association between the\ntwo, a muscle-fibre being _inoperative_ unless it be attached to a\ntendon, or connective tissue; it will contract _out_ of the body\nalthough separated from its tendon or other attachment; but _in_ the\nbody its contraction would be useless without this attachment. We must\nbear in mind that muscle-fibres are very much shorter than ordinary\nmuscles; according to the measurements of W. Krause they never exceed\n4 _cm_ in length, and usually range between 2 and 3 _cm_; their fine\npoints being fixed to the interstitial connective tissue, as the whole\nmuscle is fixed to its tendon. The function of the muscle is thus\ndependent on a due balance of its component tissues; if that balance\nis disturbed the function is disturbed. Should, from any cause, an\nexcess of muscle-fibre arise, the balance would be disturbed; should an\nencroachment of connective tissue, or of fat, take place, there would\nbe also a defect of function.\n\nHere we have the co-operation and limitation of the tissues\nillustrated; let us extend our glance, and we shall see how the\nco-operation and limitation of the organs come into play, so that\nthe resulting function depends on the balance of their forces. The\ncontractile power of each individual muscle is always limited by the\nresistance of antagonists, which prevent the muscle being contracted\nmore than about a third of its _possible_ extent, i.\u00a0e. possible when\nthere are no resistances to be overcome. Not only the increasing\ntension of antagonist muscles, but the resistance of tendons, bones,\nand softer parts must be taken into account. Thus, the increase of\nthe blacksmith\u2019s muscular power would involve a considerable increase\nin all the tissues of the arm; but such an increase would involve a\nreconstruction of his whole organism.\n\nWhenever there is an encroachment of one tissue on another, there\nis a disturbance of the normal balance, which readily passes into a\npathological state. If the brain is overrun with connective tissue, or\nthe heart with fatty tissue, we know the consequences. If connective\ntissue is deficient, epithelial runs to excess, no longer limited by\nits normal antagonist, and pus, or cancer, result.\n\n118_c_. It is unnecessary here to enlarge on this point. I have\nadduced it to show that we must extend our conception of the struggle\nfor existence beyond that of the competition and antagonism of\norganisms--the external struggle; and include under it the competition\nand antagonism of tissues and organs--the internal struggle.\nVariability is inherent in organic substances, as the result of\ntheir indefiniteness of composition (\u00a7 45_b_). This variability is\nindefinite, and is rendered definite by the competition and antagonism,\nso that every particular variation is the resultant of a composition\nof forces. The forces in operation are the internal and external\nconditions of existence--i.\u00a0e. the nature of the organism, and its\nresponse to the actions of its medium. A change may take place in\nthe medium without a corresponding response from the organism; or the\nchange may find a response and the organism become modified. Every\nmodification is a selection, determined by laws of growth; it is the\nresultant of a struggle between what, for want of a better term, may\nbe called the _organic affinities_--which represent in organized\nsubstances what chemical affinities are in the anorganized. Just as\nan organism which has been modified and thereby gained a superiority\nover others, has by this modification been _selected_ for survival--the\nselection being only another aspect of this modification--so one\ntissue, or one organ, which has surpassed another in the struggle\nof growth, will thereby have become selected. Natural Selection,\nor survival of the fittest, therefore, is simply the metaphorical\nexpression of the fact that any balance of the forces which is best\nadapted for survival will survive. Unless we interpret it as a\nshorthand expression of _all_ the internal and external conditions of\nexistence, it is not acceptable as the origin of species.\n\n118_d_. Mr. Darwin has so patiently and profoundly meditated on the\nwhole subject, that we must be very slow in presuming him to have\noverlooked any important point. I know that he has not altogether\noverlooked this which we are now considering; but he is so preoccupied\nwith the tracing out of his splendid discovery in all its bearings,\nthat he has thrown the emphasis mainly on the external struggle,\nneglecting the internal struggle; and has thus in many passages\nemployed language which implies a radical distinction where--as I\nconceive--no such distinction can be recognized. \u201cNatural Selection,\u201d\nhe says, \u201cdepends on the survival under various and complex\ncircumstances of the best-fitted individuals, but has no relation\nwhatever to the primary cause of any modification of structure.\u201d[61]\nOn this we may remark, first, that selection does not _depend_ on\nthe survival, but _is_ that survival; secondly, that the best-fitted\nindividual survives because of that modification of its structure\nwhich has given it the superiority; therefore if the primary cause\nof this modification is not due to selection, then selection cannot\nbe the cause of species. He separates Natural Selection from all the\nprimary causes of variation, either internal or external--either as\nresults of the laws of growth, of the correlations of variation, of\nuse and disuse, etc., and limits it to the slow accumulations of such\nvariations as are profitable in the struggle with competitors. And for\nhis purpose this separation is necessary. But biological philosophy\nmust, I think, regard the distinction as artificial, referring only\nto one of the great factors in the production of species. And for\nthis reason: Selection only comes into existence in the modifications\nproduced either by external or internal changes; and the selected\nchange cannot be developed further by mere inheritance, unless the\nsuccessive progeny have such a disposition of the organic affinities\nas will repeat the primary change. Inherited superiority will not by\nmere transmission become greater. The facts which are relied on in\nsupport of the idea of \u201cfixity of species\u201d show at any rate that a\ngiven superiority will remain stationary for thousands of years; and\nno one supposes that the progeny of an organism will vary unless some\nexternal or internal cause of variation accompanies the inheritance.\nMr. Darwin agrees with Mr. Spencer in admitting the difficulty of\ndistinguishing between the effects of some definite action of external\nconditions, and the accumulation through natural selection of inherited\nvariations serviceable to the organism. But even in cases where the\ndistinction could be clearly established, I think we should only see an\n_historical_ distinction, that is to say, one between effects produced\nby particular causes now in operation, and effects produced by very\ncomplex and obscure causes in operation during ancestral development.\n\n118_e_. The reader will understand that my criticism does not pretend\nto invalidate Mr. Darwin\u2019s discovery, but rather to enlarge its\nterms, so as to make it include all the biological conditions, and\nthus explain many of the variations which Natural Selection--in the\nrestricted acceptation--leaves out of account. Mr. Darwin draws a broad\nline of distinction between Variation and Selection, regarding only\nthose variations that are favorable as selected. I conceive that all\nvariations which survive are by that fact of survival, _selections_,\nwhether favorable or indifferent. A variety is a species in formation;\nnow Selection itself is not a cause, or condition, of variation, it is\nthe _expression_ of variation. Mr. Darwin is at times explicit enough\non this head: \u201cIt may metaphorically be said that Natural Selection\nis daily and hourly scrutinizing throughout the world the slightest\nvariations; rejecting those that are bad, preserving and adding up\nall that are good; silently and insensibly working, whenever and\nwherever opportunity offers, at the improvement of each organic being\nin relation to its organic and inorganic conditions of life.\u201d[62] But\nthe metaphorical nature of the term is not always borne in mind, so\nthat elsewhere Natural Selection is said to \u201cact on and modify organic\nbeings,\u201d as if it were a positive condition and not the expression\nof the modifying processes. Because grouse are largely destroyed by\nbirds of prey, any change in their color which would render them less\nconspicuous would enable more birds to escape; but it is obvious that\nthis change of color will be due to Organic Affinity; and only when\nthe change is _effected_ will there have been that selection which\n_expresses_ it. Mr. Darwin\u2019s language, however, is misleading. He\nsays: \u201cHence Natural Selection might be most effective in _giving_ the\nproper color to each kind of grouse, and in _keeping_ that color when\nonce acquired.\u201d This is to make Selection an agent, a condition of\nthe development of color; which may be accepted if we extend the term\nso as to include the organic changes themselves. Again: \u201cSome writers\nhave imagined that Natural Selection _induces variability_, whereas it\nonly implies the _preservation_ of such variations as are beneficial to\nthe being under its conditions of life.\u201d It, however, is made to imply\nmore than this, namely, the accumulation and further modification of\nsuch variations. \u201cThe mere existence of individual variability and of\nsome well-marked varieties, though necessary as the foundation, helps\nus but little in understanding how species arise in nature. How have\nall those exquisite adaptations of one part of the organization to\nanother part, and to the conditions of life, and of one organic being\nto another being, been perfected?\u201d My answer to this question would\nbe: By Organic Affinity, and the resulting struggle of the tissues and\norgans, the consequences of which are that very _adaptation_ of the\norganism to external conditions, which is expressed as the _selection_\nof the structures best adapted. The selections are the results of the\nstruggle, according to my proposed extension of the term \u201cstruggle.\u201d\nMr. Darwin defines the struggle: \u201cThe dependence of one being on\nanother, and including (what is more important) not only the life of\nthe individual but success in leaving progeny.\u201d This definition seems\ndefective, since it omits the primary and more important struggle\nwhich takes place between the organic affinities in operation. To\nsucceed in the struggle with competitors, the organism must have first\nacquired--by selection--a superiority in one or more of its organs.\n\n118_f_. A little reflection will disclose the importance of keeping\nour eyes fixed on the internal causes of variation, as well as on the\nexternal conditions of the struggle. Mr. Darwin seems to imply that the\nexternal conditions which cause a variation are to be distinguished\nfrom the conditions which accumulate and perfect such variation, that\nis to say, he implies a radical difference between the process of\nvariation and the process of selection. This, I have already said, does\nnot seem to me acceptable; the selection, I conceive, to be simply the\nvariation which has survived.[63]\n\nIf it be true that a Variety is an incipient Species and shows\nus Species in formation, it is in the same sense true that a\nvariation is an incipient organ. A species is the result of a slowly\naccumulating divergence of structure; an organ is the result of a\nslowly accumulating differentiation. At each stage of differentiation\nthere has been a selection, but we cannot by any means say that this\nselection was determined by the fact of its giving the organism a\nsuperiority over rivals, inasmuch as during all the early stages,\nwhile the organ was still in formation, there could be no advantage\naccruing from it. One animal having teeth and claws developed will\nhave a decided superiority in the struggle over another animal that\nhas no teeth and claws; but so long as the teeth and claws are in an\nundeveloped state of mere preparation they confer no superiority.\n\n118_g_. Natural Selection is only the expression of the results of\nobscure physiological processes; and for a satisfactory theory of such\nresults we must understand the nature of the processes. In other words,\nto understand Natural Selection we must recognize not only the facts\nthus expressed, but the factors of these facts,--we must analyze the\n\u201cconditions of existence.\u201d As a preliminary analysis we find _external\nconditions_, among which are included not only the dependence of the\norganism on the inorganic medium, but also the dependence of one\norganism on another,--the competition and antagonism of the whole\norganic world; and _internal conditions_, among which are included not\nonly the dependence of the organism on the laws of composition and\ndecomposition whereby each organite and each tissue is formed, but also\nthe dependence of one organite and one tissue on all the others--the\ncompetition and antagonism of all the elements.\n\nThe changes wrought in an organism by these two kinds of conditions\ndetermine Varieties and Species. Although many of the changes are due\nto the process of natural selection brought about in the struggle\nwith competitors and foes, many other changes have no such relation\nto the external struggle, but are simply the results of the organic\naffinities. They may or they may not give the organism a greater\nstability, or a greater advantage over rivals; it is enough that they\nare no disadvantage to the organism, they will then survive by virtue\nof the forces which produced them.\n\n119. The position thus reached will be important in our examination\nof the Theory of Descent by which Mr. Darwin tentatively, and his\nfollowers boldly, explain the observed resemblances in structure and\nfunction as due to blood-relationship. The doctrine of Evolution\naffirms that all complex organisms are evolved by differentiation from\nsimpler organisms, as we see the complex organ evolved from simpler\nforms. But it does not necessarily affirm that the vast variety of\norganisms had one starting-point--one ancestor; on the contrary, I\nconceive that the principles of Evolution are adverse to such a view,\nand insist rather on the necessity of innumerable starting-points. Let\nus consider the question.\n\nThat the Theory of Descent explains many of the facts must be admitted;\nbut there are many which it leaves obscure; and Mr. Darwin, with\nthat noble calmness which distinguishes him, admits the numerous\ndifficulties. Whether these will hereafter be cleared away by an\nimprovement in the Geological Record, now confessedly imperfect, or\nby more exhaustive exploration of distant countries, none can say;\nbut, to my mind, the probability is, that we shall have to seek our\nexplanation by enlarging the idea of Natural Selection, subordinating\nit to the laws of Organic Affinity. It does not seem to me, at present,\nwarrantable to assume Descent as the sole principle of morphological\nuniformities; there are other grounds of resemblance beyond those of\nblood-relationship; and these have been too much overlooked; yet a\nbrief consideration will disclose that similarity in the physiological\nlaws and the conditions of Organic Affinity must produce similarity\nin organisms, independently of relationship; just as similarity in\nthe laws and conditions of inorganic affinity will produce identity\nin chemical species. We do not suppose the carbonates and phosphates\nfound in various parts of the globe, or the families of alkaloids and\nsalts, to have any nearer kinship than that which consists in the\nsimilarity of their elements and the conditions of their combination.\nHence, in organisms, as in salts, morphological identity may be due\nto a community of conditions, rather than community of descent. Mr.\nDarwin justly holds it to be \u201cincredible that individuals identically\nthe same should have been produced through Natural Selection from\nparents _specifically distinct_,\u201d but he, since he admits analogous\nvariations, will not deny that identical forms might issue from parents\nhaving widely different origins, provided that these parent forms\nand the conditions of their reproduction were identical, as in the\ncase of vegetable and animal resemblances. To deny this would be to\ndeny the law of causation. And that which is true of identical forms\nunder identical conditions is true of similar forms under similar\nconditions. When History and Ethnology reveal a striking uniformity in\nthe progression of social phases, we do not thence conclude that the\nnations are directly related, or that the social forms have a common\nparentage; we conclude that the social phases are alike because they\nhave had common causes. When chemists point out the uniformity of type\nwhich exists in compounds so diverse in many of their properties as\nwater and sulphuretted or selenetted hydrogen, and when they declare\nphosphoretted hydrogen to be the congener of ammonia, they do not mean\nthat the one is descended from the other, or that any closer link\nconnects them than that of resemblance in their elements.\n\nIn the case of vegetal and animal organisms, we observe such a\ncommunity of elementary substance as of itself to imply a community in\ntheir laws of combination; and under similar conditions the evolved\nforms must be similar. With this community of elementary substance,\nthere are also diversities of substance and of co-operant conditions;\ncorresponding with these diversities there must be differences of\nform. Thus, although observation reveals that the bond of kinship does\nreally unite many widely divergent forms, and the principle of Descent\nwith Natural Selection will account for many of the resemblances and\ndifferences, there is at present no warrant for assuming that all\nresemblances and differences are due to this one cause, but, on the\ncontrary, we are justified in assuming a deeper principle which may be\nthus formulated: All the complex organisms are evolved from organisms\nless complex, as these were evolved from simpler forms; the link which\nunites all organisms is not always the common bond of heritage, but the\nuniformity of organized substance acting under similar conditions.\n\nIt is therefore consistent with the hypothesis of Evolution to admit a\nvariety of origins or starting-points, though not consistent to admit\nthe sudden appearance of complex Types, such as is implied in the\nhypothesis of specific creations.\n\n119 _a_. The analogies of organic forms and functions demand a more\nexhaustive scrutiny than has yet been given them. Why is it that\nvessels, nerves, and bones _ramify_ like branches, and why do these\nbranches take on the aspect of many crystalline forms? Why is it that\ncavities are constantly prolonged in ducts, e.\u00a0g. the mouth succeeded\nby the \u0153sophagus, the stomach by the intestines, the bladder by the\nurethra, the heart by the aorta, the ovary by the oviduct, and so\non? Why are there never more than four limbs attached to a vertebral\ncolumn, and these always attached to particular vertebr\u00e6? Why is\nthere a tendency in certain tissues to form tubes, and in these tubes\ncommonly to assume a muscular coat?[64] To some of these queries an\nanswer might be suggested which would bring them under known physical\nlaws. I merely notice them here for the sake of emphasizing the fact\nthat such analogies lie deeply imbedded in the laws of evolution, and\nthat what has been metaphorically called organic crystallization will\naccount for many similarities in form, without forcing us to have\nrecourse to kinship. To take a very simple case. No one will maintain\nthat the crystalline forms of snow have any kinship with the plants\nwhich they often resemble. Mr. Spencer has noticed the development\nof a wing-bearing branch from a wing of the _Ptilota plumosa_, when\nits nutrition is in excess. \u201cThis form, so strikingly like that of the\nfeathery crystallizations of many inorganic substances, proves to us\nthat in such crystallizations the simplicity or complexity of structure\nat any place depends on the quantity of matter that has to be polarized\nat that place in a given time. How the element of time modifies the\nresult, is shown by the familiar fact that crystals rapidly formed\nare small, and that they become larger when they are formed more\nslowly.\u201d[65]\n\nIt may be objected, and justly, that in the resemblance between\ncrystals and organisms the analogy is purely that of form, and usually\nconfined to one element, whereas between organisms there is resemblance\nof substance no less than of form, and usually the organisms are alike\nin several respects. The answer to this objection is, that wherever\nthere is a similarity in the causal conditions (substance and history)\nthere must be a corresponding similarity in the results; if this\nsimilarity extends to only a few of the conditions, the analogy will\nbe slight; if to several, deep. But whether slight or deep we are not\njustified, simply on the ground of resemblance, in assuming, short of\nevidence, that because they are alike, two organisms are related by\ndescent from a common ancestor.\n\n120. Let us glance at a few illustrations. It has been urged as a\nserious objection to Mr. Darwin\u2019s hypothesis,[66] that it fails to\nexplain the existence of phosphorescent organs in a few insects; and\ncertainly, when one considers the widely different orders in which\nthese organs appear, and their absence in nearly related forms, it\nis a difficulty. In noctiluc\u00e6, earthworms, molluscs, scolopendra,\nand fireflies, we may easily suppose the presence of similar organic\nconditions producing the luminosity; but it requires a strong faith to\nassign Descent as the cause.[67] We may say the same of the electric\norgans possessed by seven species of fish, belonging to five widely\nseparated genera. Although each species appears to have a limited\ngeographical range, one or the other is found in almost every part\nof the globe. These organs occupy different positions, being now on\neach side of the head, now along the body, and now along the tail;\nand in different species they are innervated from different sources.\nTheir intimate structure also varies; as appears from the remarkable\ninvestigations of Max Schultze.[68] They cannot, therefore, be\nhomologous. How could they have arisen? Not by the slow accumulations\nof Natural Selection, because, until the organs were fully formed, they\ncould be of no advantage in the struggle; hence the slow growth of\nthe organ must have proceeded without the aid of an advantage in the\nstruggle--in each case from some analogous conditions which produced\na differentiation in certain muscles. The fundamental resemblance to\nmuscles was pointed out by Carus long ago. It has been insisted on by\nLeydig:[69] and Owen says, \u201cThe row of compressed cells constituting\nthe electric prism of the Torpedo offers some analogy to the row of\nmicroscopic discs of which the elementary muscle fibre appears to\nconsist.\u201d[70] We must not, however, forget that these resemblances are\nmerely such as suggest that the electric organ is a _differentiation_\nof the substance which elsewhere becomes muscular, and that Dr.\nDavy was justified in denying the organ to be muscular.[71] That it\nis substituted for muscle cannot be doubted. Now, although we are\nentirely ignorant of the conditions which cause this differentiation of\nsubstance which elsewhere becomes muscular, but here becomes electric\norgans, we can understand that, when once such a development had\ntaken place, if it in any way profited the fish in its struggle for\nexistence, Natural Selection would _tend_ to its further increase and\npropagation. So far Mr. Darwin carries us with him; but we decline\nproceeding further. The development of these organs in fishes so widely\nremoved, does not imply an ancestral community. It is interpretable as\nmere growth on a basis once laid; and therefore would occur with or\nwithout any advantage in the struggle with rivals. The similarity in\nconcurrent conditions is quite enough to account for the resemblance\nin structure. This, with his accustomed candor, Mr. Darwin admits. \u201cIf\nthe electric organs,\u201d he says, \u201chad been inherited from one ancient\nprogenitor thus provided, we might have expected that all electric\nfishes would be specially related to each other. Nor does Geology at\nall lead to the belief that formerly most fishes had electric organs\nwhich most of their modified descendants have lost.\u201d\n\n121. It may seem strange that he should urge a difficulty against\nhis hypothesis when it could be avoided by the simple admission that\neven among nearly allied animals great differences in development\nare observable, and the electric organs might be ranged under such\ndiversities. But Mr. Darwin has so thoroughly wrought out his scheme,\nthat he foresees most objections, and rightly suspects that if this\nprinciple of divergent development be admitted, it will cut the ground\nfrom under a vast array of facts which his hypothesis of Descent\nrequires.\n\nThe sudden appearance of new organs, not a trace of which is\ndiscernible in the embryo or adult form of organisms lower in the\nscale,--for instance, the phosphorescent and electric organs,--is\nlike the sudden appearance of new instruments in the social organism,\nsuch as the printing-press and the railway, wholly inexplicable\non the theory of Descent,[72] but is explicable on the theory of\nOrganic Affinity. For observe: if we admit that differentiations\nof structure, and the sudden appearance of organs, can have arisen\nspontaneously--i.\u00a0e. not hereditarily--as the outcome of certain\nchanged physical conditions, we can hardly refuse to extend to the\nwhole organism what we admit of a particular organ. If, again, we\nadmit that organs very similar in structure and function spontaneously\nappear in organisms of widely different kinds--e.\u00a0g. the phosphorescent\nand electric organs--we must also admit that similar resemblances may\npresent themselves in organisms having a widely different parentage;\nand thus the admission of the spontaneous evolution of closely\nresembling organs carries with it the admission of the spontaneous\nevolution of closely resembling organisms: that the protoplasm of\nmuscular tissue should, under certain changed conditions, develop\ninto the tissue of electric organs, is but one case of the law that\norganized substance will develop into organisms closely resembling each\nother when the conditions have been similar.\n\n122. It is to be remarked that Mr. Darwin fixes his attention somewhat\ntoo exclusively on the adaptations which arise during the external\nstruggle for existence, and to that extent neglects the laws of organic\naffinity; just as Lamarck too exclusively fixed his attention on the\ninfluence of external conditions and of wants. Not that Mr. Darwin can\nbe said to overlook the organic laws; he simply underestimates the part\nthey play. Occasionally he seems arrested by them, as when instancing\nthe \u201ctrailing palm in the Malay Archipelago, which climbs the loftiest\ntrees by the aid of exquisitely constructed hooks, clustered around\nthe ends of the branches, and this contrivance no doubt is of the\nhighest service to the plant; but as there are nearly similar hooks\non many trees which are not climbers, the hooks on the palm may have\narisen from unknown laws of growth, and have been subsequently taken\nadvantage of by the plant undergoing further modification and becoming\na climber.\u201d\n\n123. I come round to the position from which I started, that the\nresemblances traceable among animals are no proof of kinship; even a\nresemblance so close as to defy discrimination would not, in itself,\nbe such a proof. The absolute identity of chalk in Australia and in\nEurope is a proof that there was absolute identity in the formative\nconditions and the constituent elements, but no proof whatever that the\ntwo substances were originally connected by genesis. In like manner\nthe similarity of a plant or animal in Africa and Europe may be due\nto a common kinship, but it may also be due to a _common history_. It\nis indeed barely conceivable that the history, from first to last,\nwould ever be so rigorously identical in two parts of the globe as\nto produce complex identical forms in both; because _any_ diversity,\neither in structure or external conditions, may be the starting-point\nof a wide diversity in subsequent development; and the case of organic\ncombinations is so far unlike the inorganic, that while only one form\nis possible to the latter (chalk is either formed or not formed), many\nforms are possible to organic elements owing to the complexity and\nindefiniteness of organic composition. But although forms so allied as\nthose of Species are not readily assignable to an identical history\nin different quarters of the globe, it is not only conceivable, but\nis eminently probable, that Orders and Classes have no nearer link of\nrelationship than is implied in their community of organized substance\nand their common history. The fact that there is not a single mammal\ncommon to Europe and Australia is explicable, as Mr. Darwin explains\nit, on the ground that migration has been impossible to them; but it\nis also explicable on the laws of Evolution--to have had mammals of\nthe same species and genera would imply a minute coincidence in their\nhistory, which is against the probabilities. Again, in the Oceanic\nIslands there are no Batrachians; but there are Reptiles, and these\nconform to the reptilian type. Mr. Darwin suggests that the absence of\nBatrachia is due to the impossibility of migration, their ova being\ndestroyed by salt water. But may it not be due to the divergence\nfrom the reptilian type, which was effected elsewhere, not having\ntaken place in these regions? When we find the metal Tin in Prussia\nand Cornwall, and nowhere else in Europe, must we not conclude that\nin these two countries, and nowhere else, a peculiar conjunction of\nconditions caused this peculiar evolution?\n\n124. The question at issue is, Are the resemblances observable\namong organic forms due to remote kinship, and their diversities\nto the divergences caused by adaptation to new conditions? or\nare the resemblances due to similarities, and the diversities to\ndissimilarities in the _substance and history_ of organic beings?\nAre we to assume one starting-point and one centre of creation, or\nmany similar starting-points at many centres? So far from believing\nthat all plants and animals had their origin in one primordial cell,\nat one particular spot, from which descendants migrated and became\ndiversified under the diverse conditions of their migration, it seems\nto me more consistent with the principle of Evolution to admit a vast\nvariety of origins more or less resembling each other; and this initial\nresemblance will account for the similarities still traceable under\nthe various forms; while the _early differences_, becoming intensified\nby development under different conditions, will yield the diversities.\nThe evolution of organisms, like the evolution of crystals, or the\nevolution of islands and continents, is determined, 1st, by laws\n_inherent in the substances evolved_, and, 2d, by relations to the\nmedium in which the evolution takes place. This being so, we may\n_\u00e0 priori_ affirm that the resultant forms will have a community\nstrictly corresponding with the resemblance of the substances and\ntheir conditions of evolution, together with a diversity corresponding\nwith their differences in substance and conditions. It is usually\nsupposed that the admission of separate \u201ccentres of creation\u201d is\ntantamount to an admission of \u201csuccessive creations\u201d as interpreted by\nthe majority of those who invoke \u201ccreative fiats.\u201d But the doctrine\nof Evolution, which regards Life as making its appearance _consequent\nupon a concurrence of definite conditions_, and regards the specific\nforms of Life as the necessary consequences of special circumstances,\nmust also accept the probability of similar conditions occurring at\ndifferent times and in different places. Upon what grounds, cosmical\nor biological, are we to assume that on only _one_ microscopic spot of\nthis developing planet such a group of conditions was found--on only\none spot a particle of protein substance was formed out of the abundant\nelements, and under conditions which caused it to grow and multiply,\ntill in time its descendants overran the globe? The hypothesis that\nall organic forms are the descendants of a single germ, or of even\na few germs, and are therefore united by links of kinship more or\nless remote, is not more acceptable than the hypothesis that all\nthe carbonates and phosphates, all the crystals, and all the strata\nfound in different parts of the globe, are the _descendants of a\nsingle molecule_, or a few molecules; or,--since this may seem too\nextravagant,--than that the various maladies which afflict organic\nbeings are, in a literal sense, members of _families_ having a nearer\nrelationship than that of being the phenomena manifested by similar\norgans under similar conditions--a conception which might have been\naccepted by those metaphysical pathologists who regarded Disease as\nan entity. Few philosophers have any hesitation in supposing that\nother planets besides our own are peopled with organic forms, though,\nfrom the great differences in the conditions, these forms must be\nextremely unlike those of our own planet. If separate worlds, why not\nseparate centres? The conclusion seems inevitable that wherever and\nwhenever the state of things permitted that peculiar combination of\nelements known as organized substance, there and then a centre was\nestablished--Life had a root. From roots closely resembling each other\nin all essential characters, but all more or less different, there have\nbeen developed the various stems of the great tree. Myriads of roots\nhave probably perished without issue; myriads have developed into forms\nso ill-adapted to sustain the fluctuations of the medium, so ill-fitted\nfor the struggle of existence, that they became extinct before even our\norganic record begins; myriads have become extinct since then; and the\ndescendants of those which now survive are like the shattered regiments\nand companies after some terrific battle.\n\n125. There seems to me only one alternative logically permissible to\nthe Evolution Hypothesis, namely, that all organic forms have had\neither a single origin, or else numerous origins; in other words, that\na primordial cell was the starting-point from which all organisms\nhave been successively developed; or that the development issued\nfrom many independent starting-points, more or less varied. This is\napparently not the aspect presented by the hypothesis to many of its\nadvocates; they seem to consider that if all organic forms are not the\nlineal descendants of one progenitor, they must at any rate be the\ndescendants of not more than four or five. The common belief inclines\nto one. Mr. Darwin, whose caution is as remarkable as his courage, and\nwhose candor is delightful, hesitates as to which conclusion should\nbe adopted: \u201cI cannot doubt,\u201d he says, \u201cthat the theory of descent,\nwith modifications, embraces all the members of the same class. I\nbelieve that animals have descended from, at most, only four or five\nprogenitors, and plants from an equal or lesser number. Analogy would\nlead me one step further, namely, to the belief that all animals and\nplants have descended from some one prototype. But analogy may be a\ndeceitful guide.\u201d\n\n126. I cannot see the evidence which would warrant the belief that Life\noriginated solely in one microscopic lump of protoplasm on one single\npoint of our earth\u2019s surface; on the contrary, it is more probable that\nfrom innumerable and separate points of this teeming earth, myriads\nof protoplast sprang into existence, _whenever_ and _wherever_ the\nconditions of the formation of organized substance were present. It is\nprobable that this has been incessantly going on, and that every day\nnew protoplasts appear, struggle for existence, and serve as food for\nmore highly organized rivals; but whether an evolution of the lower\nforms is, or is not, still going on, there can be no reluctance on\nthe part of every believer in Evolution to admit that when organized\nsubstance was first evolved, it was evolved at many points. If this be\nso, the community observable in organized substance, wherever found,\nmay as often be due to the fact of a common elementary composition as\nto the fact of inheritance. If this be so, we have a simple explanation\nboth of the fundamental resemblances which link all organisms together,\nand of the characteristic diversities which separate them into\nkingdoms, classes, and orders. The resemblances are many, and close,\nbecause the forms evolved had a similar elementary composition, and\ntheir stages of evolution were determined by similar conditions.\nThe diversities are many, because the forms evolved had from the\nfirst some diversities in elementary composition, and their stages of\nevolution were determined under conditions which, though similar in\ngeneral, have varied in particulars. Indeed, there is no other ground\nfor the resemblances and differences among organic beings than the\nsimilarities and dissimilarities in their Substance and History; and,\nwhether the similarities are due to blood-relationship, or to other\ncauses, the results are the same. There is something seductive in the\nsupposition that Life radiated from a single centre in ever-increasing\ncircles, its forms becoming more and more various as they came under\nmore various conditions, until at last the whole earth was crowded\nwith diversified existences. \u201cFrom one cell to myriads of complex\norganisms, through countless \u00e6ons of development,\u201d is a formula of\nspeculative grandeur, but I cannot bring myself to accept it; and I\nthink that a lingering influence of the tradition of a \u201ccreative fiat\u201d\nmay be traced in its conception. May we not rather assume that the\nearth at the dawn of Life was a vast germinal membrane, every slightly\ndiversified point producing its own vital form; and these myriads upon\nmyriads of forms--all alike and all unlike--urged by the indwelling\ntendencies of development, struggled with each other for existence,\nmany failing, many victorious, the victors carrying their tents into\nthe camping ground of the vanquished. The point raised is the immense\nimprobability of organized substance having been evolved only in one\nmicroscopic spot; if it were evolved at more than one spot, and under\nslightly varying conditions, there would necessarily have arisen in\nthese earliest formations the _initial_ diversities which afterwards\ndetermined the essential independence and difference of organisms.\n\n129. Let us for a moment glance at the resemblances and diversities\nobservable in all organisms. All have a _common basis_, all being\nconstructed out of the same fundamental elements: carbon, hydrogen,\nnitrogen, and oxygen; these (the organogens, as they are named),\nwith varying additions of some other elements, make up what we know\nas Organic Substance, vegetal and animal. Another peculiarity all\norganisms have in common, namely, that their matter is neither solid\nnor liquid, but viscid. Beside this community of _Substance_ we must\nnow place a community of _History_. All organisms grow and multiply by\nthe same process; all pass through metamorphic stages ending in death;\nall, except the very simplest, differentiate parts of their substance\nfor special uses, and these parts (cilia, membranes, tubes, glands,\nmuscles, nerves) have similar characters in whatever organism they\nappear, and their development is always similar, so that the muscles or\nnerves of an intestinal worm, a lobster, or a man, are in structure and\nhistory fundamentally alike. When, therefore, we see that there is no\nbiological character of fundamental importance which is not universal\nthroughout the organic world, when we see that in Structure and History\nall organisms have a community pervading every variety, it is difficult\nnot to draw the conclusion that some hidden link connects all organisms\ninto one; and when, further, it is seen that the most divergent forms\nmay be so arranged by the help of intermediate forms only slightly\nvarying one from the other, that the extreme ends--the monad and the\nman--may be connected, and a genealogical tree constructed, which\nwill group all forms as modified descendants from a single form, the\nhypothesis that kinship is the bidden link of which we are in search\nbecomes more and more cogent.\n\n130. But now let the other aspect be considered. If there is\nan unmistakable uniformity, there is also a diversity no less\nunmistakable. The chemical composition of organic substances is\nvarious. Unlike inorganic substances, the composition of which is\nrigorously definite, organic substances are, within narrow limits,\nvariable in composition (\u00a7 45).\n\nI pass over the resemblances and differences observed in the earliest\nstages of development, marked as they are, and direct attention to the\nfact, that down at what must be considered the very lowest organic\nregion, we meet with differences not less striking than those met with\nin the highest, we find structures (if structures they may be called),\nwhich cannot be affiliated, so widely divergent is their composition.\nThe structureless vibrio, for example, is not only capable of living\nin a medium destitute of Oxygen, but is, according to M. Pasteur,\nactually killed by oxygen; whereas the equally simple bacteria can\nno more dispense with Oxygen than other animals can. Consider for a\nmoment the differences implied in the fact that one organism cannot\neven form an enveloping membrane to contain its protoplasm, whereas\nanother contrives to secrete an exquisite shell; yet between the\nnaked Rhizopod and the shelled Rhizopod our lenses and reagents fail\nto detect a difference. One Monad can assimilate food of only one\nkind, another Monad assimilates various kinds.[73] What a revelation\nof chemical differences appears in the observations of M. Pasteur\nrespecting the vibrio and bacteria, in a fermentescible liquid--the\nformer beginning the putrid fermentation which the latter completes!\nWe cannot doubt that some marked difference must exist between the\nsingle-celled organism which produces alcoholic fermentation, and that\nwhich produces acetic fermentation, and that again which produces\nbutyric fermentation; and if we find distinctions thus established\nat the lowest region of the organic series, we need not marvel if\nthe distinctions become wider and more numerous as the series becomes\nmore diversified. The structure and development of an organism are\ndependent on the affinities of its constituent molecules, and it is\na biological principle of great importance which Sir James Paget\ninsists on, when he shows how \u201cthe existence of certain materials\nin the blood may determine the formation of structures in which\nthey may be incorporated.\u201d[74] _Any_ initial diversity may thus\nbecome the starting-point of a considerable variation in subsequent\nevolution.[75] Thus, supposing that on a given spot there are a dozen\nprotoplasts closely resembling each other, yet each in some one detail\nslightly varying; if this variation is one which, by its relations to\nthe external medium, admits of a difference in the assimilation of\nmaterials present in the medium, it may be the origin of some _new\ndirection_ in development, and the ultimate consequence may be the\nformation of a shell, an internal skeleton, a muscle, or a nerve.\nWere this not so, it would be impossible to explain such facts as\nthat chitine is peculiar to the Articulata, cellulose to Molluscoida,\ncarbonates of lime to Mollusca and Crustacea, and phosphates to\nVertebrata--all assimilated from the same external medium. But we\nsee that from this medium one organism selects the materials which\nanother rejects; and this selection is determined by the nature of the\nstructure: which assimilates only those materials it is _fitted_ to\nassimilate. We hear a great deal of Adaptation determining changes of\nstructure and function, and are too apt to regard this process as if it\nwere not intimately dependent on a corresponding structural change. By\nno amount of external influence which left the elementary composition\nof the structure unchanged, could an organism with only two tissues\nbe developed into an organism with three or four. By no supply or\nstimulus, could an animal incapable of assimilating peroxide of iron\nacquire red blood corpuscles, although it might have the iron without\nthe corpuscles; nor could an oyster form its shell unless capable of\nassimilating carbonate of lime. For myriads of years, in seas and\nponds, under endless varieties of external conditions, the am\u0153b\u00e6 have\nlived and died without forming a solid envelope, although the materials\nwere abundant, and other organisms equally simple have formed envelopes\nof infinite variety. In all the seas, and from the earliest ages,\nzoophytes have lived, and assumed a marvellous variety of shapes and\nspecialization of functions; but although some of them have acquired\nmuscles, none have acquired true nerves, none bone. Ages upon ages\nrolled on before fishes were capable of forming bone; and thousands are\nstill incapable of forming it, though living in the same waters as the\nosseous fishes.\n\n131. \u201cLooking to the dawn of life,\u201d says Mr. Darwin (repeating an\nobjection urged against his hypothesis), \u201cwhen all organic beings, as\nwe imagine, presented the simplest structure, how could the first steps\nin advancement, or in the differentiation and specialization of parts\nhave arisen? I can make no sufficient answer; and can only say that,\nas we have no facts to guide us, all speculation would be baseless and\nuseless.\u201d\n\nWhere Mr. Darwin hesitates, lesser men need extra caution; but I\nmust risk the danger of presumption, at least so far as to suggest\nthat while an answer to this question is difficult on that dynamical\nview of Evolution which regards Function as determining Structure,\nit is less difficult on the statico-dynamical view propounded in\nthese pages; the difficulty which besets the explanation when all the\nmanifold varieties of organic forms are conceived as the successive\ndivergences from an original starting-point, is lessened when a variety\nof different starting-points is assumed, in each of which some initial\ndiversity prepared the way for subsequent differentiations; just as\nwe know that between the ovum of a vertebrate and the ovum of an\ninvertebrate, similar as they are, there is a diversity which manifests\nitself in their subsequent evolution. If Function is determined by\nStructure, and Evolution is the product of the two, it is clear that\nthe different directions in the lines of development will have their\norigin in structural differences, and not in the action of external\ncircumstances, unless these previously bring about a structural change.\nThe action of the medium on the organism is assuredly a potent factor\nwhich Biology cannot ignore: but the organism itself is a factor, and\naccording to its nature the influence of the medium is defined. (\u00a7 118.)\n\n132. Quitting for a moment the track of this argument, let us glance\nat the resemblances and differences observable in Plants and Animals,\nbecause most people admit that these have separate origins. The\nresemblances are scarcely less significant than those existing among\nanimals. Both have a similar basis of elementary composition; not only\nare both formed out of protoplasts with similar properties, but in both\nthe first step from the protoplasm to definite structure is the Cell.\nAnd the life of this Cell is remarkably alike in both, its phases of\ndevelopment being in many respects identical; nay, even such variations\nas obtain in the cell-membranes are curiously linked together by a\ncommunity in the formative process.[76] In both Plants and Animals\nwe find individuals constituted--1st, by single cells; 2d, by groups\nof cells undistinguishable among each other; and 3d, by groups of\ndifferentiated cells. In both we find colonies of individuals leading\na common life. In both the processes of Nutrition and Reproduction\nare essentially similar; both propagate sexually and asexually; both\nexhibit the surprising phenomena of parthenogenesis and alternate\ngenerations. In both there are examples of a free-roving embryo which\nin maturity becomes fixed to one spot, losing its locomotive organs\nand developing its reproductive organs. In both the development of the\nreproductive organs is the climax which carries Death. So close is the\nanalogy between plant-life and animal-life, that it even reaches the\nproperties usually held to be exclusively animal; I mean that even\nshould we hesitate to accept Cohn\u2019s discovery of the muscles in certain\nplants,[77] we cannot deny that plants exhibit Contractility; and\nshould we refuse to interpret as Sensibility the phenomena exhibited by\nthe Sensitive Plants, we cannot deny that they present a very striking\nanalogy to the phenomena of Sensibility exhibited by animals.\n\n133. It is unnecessary to continue this enumeration, which might easily\nbe carried into minute detail. A chapter of such resemblances would\nonly burden the reader\u2019s mind, without adding force to the conclusion\nthat a surprising community in Substance and Life-history must be\nadmitted between Plants and Animals. This granted, we turn to the\ndifferences, and find them no less fundamental and detailed. Chemistry\ntells us nothing of the differences in the protoplasms from which\nanimals and plants arise; but that initial differences must exist is\nproved by the divergence of the products. The vegetable cell is not\nthe animal cell; and although both plants and animals have albumen,\nfibrine, and caseine, the _derivatives_ of these are unlike. Horny\nsubstance, connective tissue, nerve tissue, chitine, biliverdine,\ncreatine, urea, hippuric acid, and a variety of other products of\nevolution or of waste, never appear in plants; while the hydrocarbons\nso abundant in plants are, with two or three exceptions, absent from\nanimals. Such facts imply differences in elementary composition; and\nthis result is further enforced by the fact that where the two seem\nto resemble, they are still different: the plant protoplasm forms\nvarious cells, but never forms a cartilage-cell or nerve-cell; fibres,\nbut never a fibre of elastic tissue; tubes, but never a nerve tube;\nvessels, but never a vessel with muscular coatings; solid \u201cskeletons,\u201d\nbut always from an organic substance (_cellulose_), not from phosphates\nand carbonates. In no one character can we say that the plant and the\nanimal are identical; we can only point throughout the two kingdoms to\na great similarity accompanying a radical diversity.\n\n134. Having brought together the manifold resemblances, and the no\nless marked diversities, we must ask what is their significance? Do\nthe resemblances imply a community of origin, an universal kinship?\nIf so, the diversities will be nothing more than the divergences\nwhich have been produced by variations in the Life-history of the\nseveral groups. Or--taking the alternative view--do the diversities\nimply radical differences of origin? If so, the resemblances will be\nnothing more than the inevitable analogies resulting from Organized\nSubstance being everywhere somewhat similar in composition, and similar\nin certain phases of evolution. To state the former position in the\nsimplest way, we may assume that of two masses of protoplasm having\na common parentage, one, by the accident of assimilating a certain\nelement not brought within the range of the other, thereby becomes so\ndifferentiated as to form the starting-point of a series of evolutions\nwidely divergent from those possible to its congener; and at each stage\nof evolution the introduction of a new element (made possible by that\nstage) will form the origin of a new variation. It is thus feasible to\nreduce all organic forms to a primordial protoplasm, in the evolutions\nof which successive differentiations have been established. On the\nother hand, it is equally feasible to assume that the existence of\nradical differences must be invoked to account for the possibility of\nthe successive differentiations.\n\n135. The hunt after resemblances has led to much mistaken speculation;\nand with reference to the topic now before us, it may be urged,\nthat although by attaching ourselves to the points of community, in\ndisregard of the diversities, we may make it appear that all animals\nhave a common parentage, and that plants and animals are merely\ndivergent groups of the same prototype, a rigorous logic will force us\nonwards, and compel us to admit that a kinship no less real unites\nthe organic with the inorganic world. For upon what principle are we\nto pause at the cell or protoplasm? If by a successive elimination\nof differences we reduce all organisms to the cell, we must go on\nand reduce the cell itself to the chemical elements out of which it\nis constructed; and inasmuch as these elements are all common to the\ninorganic world, the only difference being one of synthesis, we reach a\nresult which is the stultification of all classification, namely, the\nassertion of a kinship which is universal. We must bear in mind that\nall things may be reduced to a common root by simply disregarding their\ndifferences. All things are alike when we set aside their unlikeness.\n\n136. Suppose, for the sake of illustration, we regard an Orchestra\nin the light of the Development Hypothesis. The various instruments\nof which it is composed have general resemblances and particular\ndifferences, not unlike those observable in various organisms; and\nas we proceed in the work of classification we quickly discover that\nthey may be arranged in groups analogous to the Sub-kingdoms, Classes,\nOrders, Genera, and Species of the organic world. Each group has its\ncardinal distinction, its initial point of divergence. All musical\ninstruments resemble each other in the fundamental character of\nproducing Tone by the vibrations of their substance. This may be called\ntheir organic basis. The first marked difference which determines the\ncharacter of two sub-kingdoms (namely, instruments of Percussion and\nWind instruments) arises from a difference in the method of impressing\nthe vibrations; and the grand divisions of these sub-kingdoms arise\nfrom the nature of the vibrating substances. Each type admits of many\nmodifications, but the primary distinction is ineffaceable. We can\nconceive the Pipe modified into a Flute, a Flageolet, a Clarionet,\na Hautbois, a Bassoon, or a Fife, by simple accessory changes; to\nmodify the Pipe into a Trumpet, and thus produce the peculiar _timbre_\nof the trumpet, would be impossible except by the _substitution_\nof a new material; by replacing the wood with metal we may adhere\nto the old Type, but we have created a new Class. (Attention is\nrequested to this point, because the current views respecting the\ntransmutation of tissues, which seem to lend a decisive support to the\nhypothesis of the transmutation of species are very commonly vitiated\nby the confusion of transformation with substitution. No anatomical\nelement is _transformed_ into another specifically different--an\nepithelial-cell into a nerve-cell, for instance--but one anatomical\nelement is frequently _substituted_ for another.) To convert the Pipe\nor the Trumpet into a Violin or a Drum would be impossible. We can\nfollow the modifications of a Tambourine into a Drum or Kettle-drum,\nbut no modifications of these will yield the Cymbals. That is to say,\nthe vibrating materials--wood, metal, parchment, and the combination\nof wood and strings--have peculiar properties, and the instruments\nformed of such materials must necessarily from the very first belong\nto different groups, each subdivision of the groups being dependent on\nsome characteristic difference in methods of impressing the vibrations,\nor in the materials. Although all musical instruments have a common\nproperty and a common purpose, we do not regard them as transformations\nof one primitive instrument; their kindred nature is a subjective\nconception; the analogies are numerous and close, but we know their\norigin. It is obvious that men being pleased by musical tones, have\nbeen led by their delight to construct instruments whenever they have\ndiscovered substances capable of musical vibrations, or methods of\nimpressing such vibrations. By substituting the bow for the plectrum or\nthe fingers, they may have changed the Lyre into the Violin, Viola,\nVioloncello, and Bass. (It seems historically probable that the real\norigin of the Violin class was an instrument with one string played on\nby a bow.) By grouping together Pipes of various sizes they got the\nPanpipes; by substituting metal and enlarging the blowing apparatus\nthey got the Organ. By beating on stretched parchment with the finger,\nthey got the Tambourine and Tom-Tom; by doubling this and using a stick\nthey got the Drum. By beating metal with metal they got the Cymbals; by\nbeating wood they got the Castanets.\n\n137. The application of this illustration is plain. Just as a\nwind-instrument is incapable of becoming a stringed instrument, so\na Mollusc, with all its muscles unstriped, and its nervous system\nunsymmetrical, is incapable of becoming a Crustacean, with all its\nmuscles striped and its nervous system symmetrical. Indeed there\nare probably few biologists of the present day who imagine the\ntransmutation of one kind into the other to be possible; but many\nbiologists assume that both may have been evolved from a common root.\nThe point is beyond proof; yet I think there is a greater probability\nin the assumption that both were evolved from different roots. At any\nrate, one thing is certain; a divergence could only have been effected\nby a series of _substitutions_; and the question when and how these\nsubstitutions took place is unanswerable: one school believes them to\nhave been creative fiats, the other school believes them to have been\ntransmutations.\n\n138. When we see an annelid and a vertebrate resembling each other in\nsome special point which is not common either to their classes or to\nany intermediate classes--as when we see the wood-louse (_Oniscus_)\nand the hedgehog defend themselves in the same strange way by rolling\nup into a ball--we cannot interpret this as a trace of distant\nkinship. When we see a breed of pigeons and a breed of canaries\nturning somersaults, and one of the Bear family (_Ratel_) given to the\nsame singular habit, we can hardly suppose that this is in each case\ninherited from a common progenitor. When we see one savage race tipping\narrows with iron, and another, ignorant of iron, using poison, there is\na community of object effected by diversity of means; but the analogy\ndoes not necessarily imply any closer connection between the two races\nthan the fact that men with similar faculties and similar wants find\nout similar methods of supplying their wants. Even those who admit that\nthe human race is one family, and that the various peoples carried with\nthem a common fund of knowledge when they separated from the parent\nstock, may still point to a variety of new inventions and new social\ndevelopments which occurred quite independently of each other, yet are\nstrikingly alike. Their resemblance will be due to resemblance in the\nconditions. The existence, for example, of a religious worship, or a\nsocial institution, in two nations widely separated both in time and\nspace, and under great historical diversities, is no absolute proof\nthat these two nations are from the same stock, and that the ideas have\nthe same parentage. It may be so; it may be otherwise. It may be an\nanalogy no more implying kinship than the fact of ants making slaves\nof other ants (and these the black ants!) implies a kinship with men.\nGiven an organization which in the two nations is alike, and a history\nwhich is in certain characteristics analogous, there must inevitably\nresult religious and social institutions having a corresponding\nresemblance. I do not wish to imply that the researches of philologists\nand ethnologists are misdirected, or that their conclusions\nrespecting the kinship of mankind are to be rejected; I only urge the\nconsideration that perhaps too much stress is laid on community of\nblood, and not enough on community of conditions.\n\n\nRECAPITULATION.\n\n139. The various lines of argument may here be recapitulated. The\norganic world presents a spectacle of endless diversity, accompanied by\na pervading uniformity. The general resemblances in forms and functions\nare more or less masked by particular differences. The resemblances, it\nis said, may be all due to kinship, all the living individuals having\ndescended from a primordial cell; and at each stage of the descent the\nadaptations to new conditions may have issued in deviations from the\nancestral form, while the process of Natural Selection giving stability\nto those variations which best fitted the organism in the struggle of\nexistence, has made greater and greater gaps, and produced more marked\ndiversities among the descendants. This is the Darwinian Theory: \u201cOn my\ntheory unity of Type is explained by unity of Descent.\u201d\n\n140. By the general consent of biologists, this theory is held to\nexplain many if not all the observed facts. It is a very luminous\nsuggestion; but it requires an enlargement so as to include Organic\nAffinity; and when once this fundamental principle is admitted, it\nbrings with it very serious doubts as to the theory of Descent.\nWe are then entitled to assume that many of the most striking\nresemblances, instead of being due to kinship, are due simply to the\ngeneral principle that similar causes must have similar effects, and\nthat organic substances having a very close resemblance, organized\nsubstances must have similar stages of evolution under similar\nconditions; and thus organs will necessarily take on very similar forms\nin very different organisms (for example, the eye of the cephalopod\nand the eye of the vertebrate), and organisms having widely different\nparentage may closely resemble each other. If we are entitled to\nassume that protoplasm appeared not in one microscopic spot alone, but\nin many places and in vast quantities--and this is surely the more\njustifiable assumption--then we must also admit that these germinal\nstarting-points were from the first, or very shortly afterwards,\ndifferentiated by variations in their elementary composition. Now we\nknow that a very minute change in composition may lead to immense\ndifferences in evolution. Thus the descendants of two slightly\ndifferent progenitors may, by continual differentiation, become very\nmarkedly unlike; yet, because of the original resemblance of their\nsubstances, they will reveal a pervading similarity.\n\nWhile it is thus conceivable that all organisms may resemble each\nother, and all differ, owing to the similarities and diversities in the\n\u201cconditions of existence\u201d (and among those conditions that of descent\nis of wide range), it is not very readily conceivable how advantage\nin the external struggle could have determined the varieties of form\nand function, because many differentiations give no superiority in the\nstruggle. As Mr. St. George Mivart urges, \u201cNatural Selection utterly\nfails to account for the conservation and development of the minute and\nrudimentary beginnings, the slight and infinitesimal commencements of\nstructures, however useful those structures may afterwards become.\u201d[78]\nAnd this is undeniable on the supposition that Natural Selection is an\nagency not identical with the variations of growth, but exclusively\nconfined to the accumulation of favorable variations.\n\n141. In estimating the two hypotheses--First, of Descent from one\nprimordial germ, and the modifications _due_ to Natural Selection, or,\nas I should say, _expressed_ in Selection; and Secondly, of Descent\nfrom innumerable germs having initial differences, which differences\nradiated into the marked modifications, there is this superiority to\nbe claimed for the first, that it is more easily handled as an aid to\nresearch, and is therefore more decidedly useful. The laws of Organic\nAffinity are at present too obscure for any successful application.\nI only wish to point out that the theory of Descent is an imaginary\nconstruction of what _may have been_ the process of species-formation,\nnot a transcription of the process observed. It constructs an imaginary\nType as progenitor of a long line of widely different descendants. The\nannelid which is taken as the ancestor of the vertebrates is not any\nannelid known either to zo\u00f6logists or geologists, but a generalized\nand imaginary type. So daringly liberal is the imagination in endowing\nthe ancestor with whatever may be required for the descendants, that\nMr. Darwin thinks it _probable_, from what we know of the embryos\nof vertebrates, that these animals \u201care the modified descendants\nof some ancient progenitor which was furnished in its adult state\nwith branchi\u00e6, a swim-bladder, four simple limbs, and a long tail,\nall fitted for an organic life,\u201d (p. 533); and Dr. Dohrn conceives\nthe original type to have contained within itself all that has been\nsubsequently evolved in the highest vertebrate, the other and less\nelaborate organisms being mere degradations from this type.[79] This\nuse of the imagination, although not without advantages, is also not\nwithout dangers. It may direct research, it must not be suffered to\nreplace research.\n\n\n\n\nPROBLEM II.\n\nTHE NERVOUS MECHANISM.\n\n    \u201cAll the functions of the nervous system are as dependent upon its\n    structure and nature, as the accurate indication of time upon the\n    construction of the chronometer.\u201d--PROCHASKA.\n\n    \u201cUnser Wissen wird nie vollendet, ist und bleibt St\u00fcckwerk; dessen\n    Erg\u00e4nzung das Streben und Hoffen der forschenden Denker bleiben\n    wird f\u00fcr alle Zeit.\u201d--RADENHAUSEN, _Osiris_.\n\n                    \u201cOur nimble souls\n    Can spin an insubstantial universe\n    Suiting our mood, and call it possible,\n    Sooner than see one grain with eye exact,\n    And give strict record of it.\u201d\n                      GEORGE ELIOT, _The Spanish Gypsy_.\n\n    \u201cIf we compare the teachings of our books with what Nature is\n    constantly showing, we find there is no agreement between those two\n    sources of learning.\u201d--BROWN S\u00c9QUARD.\n\n\n\n\nTHE NERVOUS MECHANISM.\n\n\n\n\nCHAPTER I.\n\nSURVEY OF THE SYSTEM.\n\n\n1. Our knowledge of mental processes is derived from reflection on our\npersonal experiences, combined with inferences from our observation\nof other men and animals, under similar conditions. The processes\nare complex and variable; so complex and variable, that knowledge of\ntheir component factors can only be gained through long tentative\nstudy, aided by fortunate circumstances which present these factors\nseparately, or at any rate in such marked predominance as to fix\nattention. This subjective analysis of the _processes_ has to be\nsupplemented by, and confirmed by an objective analysis of, the\n_conditions_, external and internal: the facts of Feeling have to be\ntraced to facts of Physiology, which will exhibit that Physical Basis\nof Mind so earnestly sought by the inquirer.\n\nBoth the subjective and the objective analysis are at present in a\nvery imperfect state. Although there is much confident assertion and\n\u201cfalse persuasion of knowledge\u201d in both regions, there is, unhappily,\nlittle that can be seriously accepted as demonstrated. In the present\nvolume we shall concern ourselves almost exclusively with the objective\nanalysis, and do our utmost to mark what is mere inference from what\nis verified observation. It is only by Observation that facts can be\n_settled_; however Analogy and Inference may suggest where the truth\nmay lie, they are finger-posts, not goals. At the best they only tell\nus what Observation _would_ reveal could the processes be submitted to\nSense.\n\nIn a loose and general way every one knows that the Nervous System is\na dominant agent in all sentient processes; although not by any means\nthe only agent, yet, because of its predominance, it is artificially\naccepted as the only one. With the greater complexity of this system,\nthere is observed a corresponding increase in the variety of sentient\nphenomena. The labors of anatomists have secured a tolerably exact plan\nof the topographical distribution of this system; a somewhat chaotic\nmass of observation and inference passes as a description of its\nelementary structure. The labors of physiologists have succeeded to a\nsmall extent in localizing certain functions in certain organs of this\nsystem. But imperfect as our knowledge of the elementary structures is,\nour knowledge of the functions is still more so. I wish I could say\notherwise, and that I could ask my readers to accept with confidence\nwhat teachers confidently propound. The attitude of scepticism is\nalways repulsive; the sceptic is seldom received without disfavor,\nbecause he throws on us the labor of investigation there where we wish\nfor the confidence of knowledge. Yet it is only by facing the facts\nthat we can hope one day to solve the great questions.\n\n2. The nervous system has, in our artificial view of it, two divisions:\nthe Peripheral, which connects the organism with the external world;\nand the Central, which connects each part of the organism with all\nthe other parts. Although the system is constituted by various\ntissues--neural, connective, vascular, and elastic--it receives its\ncharacteristic designation from nerve-fibrils, nerve-fibres, and\nnerve-cells; just as the muscular system receives its designation\nfrom contractile cells and fibres. This neural tissue assumes three\nwell-marked forms: 1\u00b0, _nerves_, which are bundles of fibres and\nfibrils, enclosed in a membranous sheath; 2\u00b0, _ganglia_, which are\nclusters of cells, fibres, and fibrils, sometimes enclosed in a sheath,\nsometimes not; 3\u00b0, _centres_, which are artificial divisions of the\nneural axis, serving as points of union for different organs.\n\nIn the Invertebrata the neural axis is the chain of ganglionic masses\nrunning along the ventral side, and giving off the nerves to organs of\nsense, and to the muscles. It may be seen represented in Fig.\u00a01.\n\n[Illustration: Fig. 1.--_Nervous system of a beetle._ The small round\nmasses, or _ganglia_, are seen to be connected by longitudinal fibres,\nand from the ganglia issue fibres to the limbs, organs of sense, and\nviscera.]\n\nIn the Vertebrata the axis is dorsal, and is called the _cerebro-spinal\naxis_, including brain and spinal cord. When we look at this structure\nsuperficially we see various nerves radiating _from_ it to skin,\nglands, and muscles; but a closer examination, enlightened by knowledge\nof function, shows that some of these nerves pass _into_ it from the\nvarious surfaces and sense-organs, and are therefore called _afferent_\nor _sensory_; whereas another set passes out of it to glands and\nmuscles, and these nerves are therefore called _efferent_ or _motory_.\nThere are also fibres which, passing from one part of the great centre\nto another, are called _commissural_.\n\nTo this brief account of the cerebro-spinal system may be added a word\non the connected chain of ganglia and nerves known as the Sympathetic,\nbecause it was formerly supposed to be the organ through which the\nvarious \u201csympathies\u201d were effected. It is now held to be the system\ndevoted to the viscera and blood-vessels; but there is still great want\nof agreement among physiologists as to whether it is an independent\nsystem, having a special structure somewhat different from that of the\ncerebro-spinal, or whether it is simply a great plexus of nerves and\nganglia, only topographically distinguishable from the rest of the\nnervous system. Into this point it is unnecessary for me to enter here.\nEnough to say, that I entirely agree with Sigmund Mayer in adopting\nthe second view.[80] In no histological character, yet specified, are\nthe sympathetic nerves and ganglia demarcated from the others. There\nare, indeed, _more_ non-medullary fibres (the gray fibres of Remak)\nin the sympathetic; but the same fibres are also abundant in the\ncerebro-spinal system; and the sympathetic has also its large medullary\nfibres.\n\n3. The Centres are composed of two substances: the gray and the white.\nThe gray substance is often called the vesicular because of its\nabundant cells; but it has even more fibres than cells, and the white\nsubstance has also a few cells.[81] The gray substance is distributed\nover the surface of the brain--in the convolutions; and in various\nother parts of the encephalon. It surrounds the central canal which\nforms the ventricles of the brain and is continued as a very small\ncavity all down the spinal cord. Besides entering into the important\nand conspicuous masses known as the cerebral ganglia--(the _optic\nthalami_, and _corpora striata_)--the gray substance is massed in the\n_corpora quadrigemina_, _crura cerebri pons varolii_, and _medulla\noblongata_. We shall have occasion to refer to each of those parts.\nUntil modern times all the masses included in the skull under the\nfamiliar term Brain (or the technical term Encephalon) were regarded\nas the only centre, and also as the origin of all the nerves. Nor has\nthis notion even yet entirely disappeared, although the spinal cord\nis known not to be a large nerve trunk, but a centre or connected\nchain of centres, structurally and functionally similar to the cranial\ncentres. The shadow of the ancient error still obscures interpretation\nof the part this spinal cord plays in the sentient mechanism; and thus\nalthough the cord is universally admitted to be a centre for \u201csensitive\nimpressions,\u201d it is usually excluded from Sensation. This widespread\nand misleading notion will be critically examined in a future problem.\n\n4. Beginning our survey of the cerebro-spinal axis with the Spinal\nCord, we observe it to consist: 1\u00b0, of _central gray substance_\nsurrounding the scarcely visible canal, which is all that remains of\nthe primitive groove in the germinal membrane (\u00a7 9); 2\u00b0, irregular\ngray masses, called the _anterior and posterior horns_,[82] connected\nwith the anterior and posterior _roots_ of the spinal nerves; and 3\u00b0,\nstrands of white fibres enclosing this central substance, and called\nthe _anterior lateral and posterior columns_.\n\nLike the Cerebrum, it is a double organ formed by two symmetrical\nhalves, as the cerebrum is of two hemispheres. Each half innervates\nthe corresponding half of the body. The cord is unlike the cerebrum\nin external form, though very like it in internal structure. The gray\nstructure is mainly external in the cerebrum, and is internal in the\ncord.\n\nFrom the anterior side of the cord (that which in animals is the under\nside) the motor nerves issue; from the posterior (in animals the\nupper) side, issue the sensory nerves. On each of the sensory nerves\nthere is a ganglion. The _roots_ of each nerve, formed of several\nrootlets issuing from the anterior and posterior columns, subsequently\nunite together, and proceed in a single sheath to muscles and skin,\nseparating again, however, before they reach muscles and skin. Fig.\u00a02\nrepresents this arrangement.\n\n[Illustration: Fig.\u00a02.--_A portion of the spinal cord with its nerves_\n(after Bernard). The left-hand figure shows the anterior side; the\nright-hand the posterior. A the anterior, and P, the posterior root,\nthey meet at _g_, the ganglion; _c_ and _d_ are filaments connecting\ntwo posterior roots.]\n\n5. There are thirty-one pairs (sometimes thirty-two) of such\nnerves--namely, eight cervical, twelve thoracic, five lumbar, five\nsacral, and one (or two) coccygeal. Figs.\u00a03 to 6 represent transverse\nsections, which display the entrance of the roots of the nerves into\nthe anterior and posterior horns.\n\n6. Similar masses of gray substance in the _Medulla Oblongata_ (which\nis the name given to the cord when it passes into the skull)[83] are\nsupposed to be the origins of some other nerves (the cranial).\n\n[Illustration: Fig.\u00a03.--_Transverse section of one half of the\nspinal cord in the lumbar region_ (after K\u00f6lliker). _a_, anterior\nroot entering the anterior gray horns, _m_ and _l_, where cells are\nclustered; _c_, central canal; _d_ and _e_, the anterior and posterior\ncommissures uniting the two halves of the cord; _b_, posterior root\nentering the posterior gray horn.]\n\n[Illustration: Fig.\u00a04.--_Transverse section of both halves of the cord,\ncervical region._ _a_, Fissure separating the anterior columns; _b_,\nfissure of the posterior.]\n\n[Illustration: Fig.\u00a05.--_Transverse section of the cord in the dorsal\nregion._]\n\n[Illustration: Fig.\u00a06.--_Transverse section in the lumbar region._]\n\nAlthough the Medulla Spinalis is unquestionably continued as the\nMedulla Oblongata, the arrangement of its tissues here becomes\ngradually changed, and so complicated that it baffles the scalpel.\nAnatomists are, however, agreed on the one point of fundamental\nimportance to us here--namely, that there is only a rearrangement, not\na new tissue. Accepting the artificial division into two organs, we may\nsay that their functions are different, inasmuch as they are different\nin their anatomical connections--they innervate different parts; but as\nnerve-centres they have one and the same property.\n\nOn its posterior surface the Medulla Oblongata opens as the _fourth\nventricle_. It is then no longer a closed canal, but an expansion of\nthe spinal canal, which is covered by the Cerebellum. On its anterior\nsurface projects the _pons varolii_. Figs.\u00a07 and 8 represent these.\n\n[Illustration:\n\n    Fig.\u00a07.--_Back, or upper view of the Medulla Oblongata as it\n    continues the Med. Spinalis._ 1, Section of the thalami; 2, corpora\n    quadrigemina (the two lower bodies are imperfectly represented in\n    the engraving); 3, section of the crura cerebelli; 4, the fourth\n    ventricle; 5, the restiform bodies; 6, the calamus scriptorius.\n]\n\n[Illustration:\n\n    Fig.\u00a08.--_Front, or under view of the Med. Oblong._ 1, Optic nerves\n    cut off at the chiasma; 2, crura cerebri; 3, pons varolii; 4,\n    olivary bodies; 5, anterior pyramids; 6, spinal columns.\n]\n\nWhile thus on the one hand continuing the Medulla Spinalis, the\nMedulla Oblongata is seen on the other hand to be continuous with the\nBrain--its white columns passing upwards in the _crura cerebri_, its\ncavity repeated in the other ventricles. Above it lie the ganglionic\nmasses, the _corpora quadrigemina_, _optic thalami_, and _corpora\nstriata_. Crowning these are the big and little brains, Cerebrum and\nCerebellum. Figs.\u00a09 and 10 represent this relation of Medulla Spinalis,\nMedulla Oblongata, and Brain. Fig.\u00a011 is a purely artificial diagram\nwhich will give the reader some idea of the disposition of the white\nand gray substances.\n\n[Illustration:\n\n    Fig.\u00a09.--_Human Brain in Profile._ 1, Cerebrum; 2, cerebellum; 3,\n    pons varolii and medulla oblongata.\n]\n\n[Illustration:\n\n    Fig.\u00a010.--_One half of the Brain in Profile, from the inside._\n    1, Convolutions of the cerebrum; 2, corpus callosum or great\n    commissure uniting the two hemispheres; 3, arbor vit\u00e6 or branching\n    arrangement of gray and white matter in the cerebellum; 4, pons\n    varolii and medulla.\n]\n\n[Illustration:\n\n    Fig.\u00a011.--_Diagram of a vertical section of the Brain_ (after\n    Dalton). 1, Olfactory ganglion; 2, cerebral hemisphere; 3, corpus\n    striatum; 4, thalamus; 5, corpora quadrigemina; 6, cerebellum; 7,\n    ganglion of the pons varolii; 8, olivary body.\n]\n\n7. In man the Cerebrum is to the Cerebellum as 9 to 1. In the lower\nvertebrates the preponderance is still greater. The cerebrum is in our\nartificial systems commonly divided into three lobes. The frontal lobe\nis that portion which lies in front of the deep fissure named after\nRolando; between that fissure and the \u201cinternal perpendicular fissure\u201d\nlies the parietal lobe; behind this we have the occipital lobe; and,\nbelow the fissure of Sylvius, the tempero-sphenoidal lobe. Each lobe is\nagain subdivided according to its convolutions.\n\nThe disposition of the fibres in the brain is far too complex to be\naccurately followed. All that we can say is, that there are strands\nwhich connect one convolution with another, strands which connect\none hemisphere with another, strands which connect cerebrum with\ncerebellum, and strands which connect the cerebrum with the lower\nganglia. It is important to conceive this distinctly; for we shall\nhereafter see that the function of the Brain (by brain is here meant\nboth Cerebrum and Cerebellum) is not that of _innervation_, but of\n_incitation and regulation_. To speak metaphorically, it is the\ncoachman who holds in his hands the reins, and guides the team. One\ncardinal fact should arrest attention, namely, that not a single nerve\nin the body has its origin or centre of innervation in the cerebrum and\ncerebellum. The olfactory and optic nerves do indeed _seem_ to issue\nfrom the cerebrum; and are commonly described as cerebral nerves. But\nthe facts of Development, minute Anatomy, and Experiment prove this to\nbe inexact. Although I shall continue to speak of the olfactory and\noptic nerves in accordance with universal usage, not wishing to burden\nthe reader with unnecessary innovations, I must at the outset express\nmy opinion that these nerves cannot be brought under the same general\ntype as the other sensory nerves. Embryology and Anatomy suggest that\nthey have no more claim to the title than the _crura cerebri_. Of this\nhereafter. Setting these aside, no one now refuses to acknowledge\nthat Cerebrum and Cerebellum, although centres of Incitation and\nAssociation, are not the centres of direct Innervation: the organic\nmechanism in all its _physiological_ processes will act independently\nof them (so far as such artificial distinctions are admissible at all).\nThis does not throw a doubt on their _physiological_ functions, nor on\ntheir participation in the normal execution of physiological processes.\n\n8. From this rapid survey two important points may be selected for\nspecial attention. First, the continuity of the neural axis throughout;\nsecondly, the fundamental similarity of its _structure_, underlying\ngreat variations in its form and connections. This, which is the\nanatomical expression of the Unity of the nervous system, will become\nmore evident after we have expounded what Embryology and Microscopic\nAnatomy teach. We may therefore digress here awhile to consider\n\n\nTHE EARLY FORMS OF NERVE CENTRES.\n\n9. In the outermost layer of the germinal membrane of the embryo a\ngroove appears, which deepens as its sides grow upwards, and finally\nclose over and form a canal. This canal is composed of cells all alike.\nIts foremost extremity soon bulges into three well-marked enlargements,\nwhich are then called the _primitive cerebral vesicles_. The cavities\nof these vesicles are continuous. Except in position and size, there\nare no discernible differences in these vesicles, which are known as\nthe Fore-brain, Middle-brain, and Hind-brain.\n\n10. The _Fore-brain_ soon buds off from each side a small vesicle. This\nis the optic vesicle, the first rudiment of what subsequently becomes\noptic nerve and retina. At this period it is simply a vesicle with\na hollow stem, the cavity being continuous with the cavity of the\ncerebral vesicle, and the walls continuous with the cerebral wall.\n\nIt thus appears that the retina and optic \u201cnerve\u201d are primitive\nportions of the brain--a detached segment of the general centre,\nidentical in structure with the cerebral vesicle, and not unlike in\nform. A cup-like depression quickly forms the optic vesicle into an\ninner and an outer fold. The inner or concave fold becomes the retina,\nand the outer or convex fold (that nearest to the brain) becomes its\nchoroid membrane. On the fourth day of incubation the retina of the\nchick is composed of spindle-shaped cells, all alike. On the seventh\nday there is a differentiation into layers, one of which on the eighth\nday is granular; on the tenth two are granular; and on the thirteenth\nganglionic cells appear. Some of the cells have elongated into radial\nfibres (known as M\u00fcller\u2019s fibres); and with the appearance of rods and\ncones the normal retinal elements are complete.\n\n11. The researches of Foster and Balfour[84] confirm the statement that\nall the different parts of the retina (whether nervous or connective)\nare derived from one and the same layer of embryonic cells, which\noriginally formed a portion of the first cerebral vesicle.\n\n12. Meanwhile the hollow stem of this optic vesicle begins to develop\nfibres amidst the nuclei of its walls. The \u201coptic nerve\u201d arises: it\nis still hollow; and in birds remains so through life. The fibres as\nthey are developed _grow forwards towards the retina_, and spread over\nits internal surface. _They also grow forwards towards the brain_,\nand spread over its substance; but it is _not_, as might be supposed,\nand is generally believed, with the cerebral hemispheres (or that\nportion of the Fore-brain from which these are derived), but with the\nMiddle-brain (which becomes the _corpora quadrigemina_), that the optic\nfibres are in connection.[85]\n\n13. This will be understood when the further development is traced.\nThe Fore-brain, after budding off the optic vesicles, buds off two\nlarger vesicles--the future cerebral hemispheres. This is noticeable\non the second day of incubation, and by the third day each vesicle is\nas large as the whole of the original Fore-brain. Their development is\nessentially like that of the optic vesicles; both as to the cellular\nand the fibrous elements.\n\nThe _convolutions_, _corpus callosum_, _nucleus lentiformis_,\nand _corpora striata_ are then indicated. Meanwhile, that which\noriginally was the Fore-brain has lapsed into the secondary rank as\nIntermediate-brain (_Zwischenhirn_), and becomes the parts surrounding\nthe third ventricle, namely, the _thalami_, _corpora candicantia_,\n_infundibulum_, and what is called the \u201cposterior perforated substance.\u201d\n\n14. The _Middle-brain_, or Second Vesicle, develops the _corpora\nquadrigemina_ from the roof of its cavity, and the _crura cerebri_ from\nits floor.\n\nThe _Hind-brain_, or Third Vesicle, divides into two, like the First\nVesicle; it buds off the hemispheres of the cerebellum; its cavity\nforms the fourth ventricle; its walls the _medulla oblongata_.\n\n15. It thus appears that the primitive membrane forms into a canal,\nwhich enlarges at one part into three vesicles, and from these are\ndeveloped the encephalic structures. The continuity of the walls\nand cavities of these vesicles is never obliterated throughout the\nsubsequent changes. It is also traceable throughout the medulla\nspinalis. And microscopic investigation reveals that underneath all the\nmorphological changes the walls of the whole cerebro-spinal axis are\ncomposed of similar elements on a similar plan.[86]\n\n16. Two conclusions directly follow from this exposition:--first, that\n_since the structure of the great axis is everywhere similar, the\nproperties must be similar_; secondly, that _since there is structural\ncontinuity, no one part can be called into activity without at the same\ntime more or less exciting that of all the rest_.\n\n\nTHE PERIPHERAL SYSTEM.\n\n17. Following the analytical division, we now come to the Peripheral\nSystem of nerves and ganglia. The separation, I must often repeat,\nis purely artificial; but the artifice has conveniences. We separate\nin the same way the heart from veins and arteries, and the capillary\ncirculation from the arterial.\n\nEach nerve has its direct connection with a particular centre, and\nindirectly with the whole system. It has its circumscribed territory,\nand individual office. Except in a few cases of anastomosis, the action\nof one nerve does not involve that of another: only one muscle or one\ngroup of muscles is moved, without exciting motion in a neighbor. It is\nthrough the centres that these individual territories are united; and\na wave of excitation always passes throughout the central substance.\nThus the centres are not simply organs of association, consequently of\nregulation, but are the nexus whereby the diversity of the actions is\nintegrated into the unity of consensus.\n\n18. Nothing further need at present be stated respecting the nerves;\nbut it is needful to give precision to the ideas of\n\n\nGANGLIA AND CENTRES,\n\nusually spoken of as if they were convertible terms. That this is\ninexact may be readily shown, and that it is misleading appears in its\ncausing physiologists to credit every ganglion, wherever found, with\ncentral functions; and, by an almost inevitable extension of the error,\nhas led to the assignment of central functions to a single ganglionic\ncell! This is but part of that \u201csuperstition of the cell\u201d against\nwhich I shall have to protest. I will not here raise the doubt which\npresses from various sides respecting the central functions of the\nganglia in the heart and intestines, because the reader perhaps shares\nthe general opinion on that point; but let me simply ask what central\nfunction can possibly be assigned to the ganglia on each of the spinal\nsensory nerves? above all to those grouped and scattered ganglionic\ncells which are found at the peripheral termination of some nerves, and\nin the very trunks of others? There may, indeed, be imagined a central\nfunction for the ganglia in the mesentery, and even in the choroid coat\nof the retina, on the hypothesis (quite gratuitous, I think) of their\nregulating the circulation; but even this explanation cannot be adopted\nwith respect to the ganglionic cells which appear in the course of the\nnerve.[87]\n\nThe meaning of a physiological centre is, that it is a point _to_ which\nstimulations proceed, and _from_ which they are reflected. The meaning\nof a ganglion is, that it is a group of nerve cells dispersed among, or\nin continuation with, nerve fibres: it may be a centre of reflection,\nor it may not; and in the latter case its physiological office is at\npresent undetermined. A ganglion is no more a centre in virtue of its\ncell-group than a muscle is a limb. All function depends on connection,\nand central function demands a connection of afferent and efferent\nparts.\n\n19. The ganglia found in the ventral cord of the Invertebrate (see\nFig.\u00a01) are centres, each of which has considerable independence,\neach regulating a single segment of the body, or a group of similar\nsegments. As the scale of animal complexity ascends, these separated\ncentres tend more and more to coalesce, and with this coalescence\ncomes an increasing _combination_ of movements.[88] Observe the\ncaterpillar slowly crawling over a leaf; each segment of its body moves\nin succession; but when this caterpillar becomes a butterfly the body\nmoves rapidly, and all at once. Open the caterpillar, and you find its\nnervous centres are thirteen separate ganglia, each presiding over a\ndistinct part of the body, and each capable of independent action.\nOpen the butterfly, and you find the thirteen ganglia greatly changed:\nthe second and third are fused into one; the fourth, fifth, and sixth\ninto another; the eleventh and twelfth into another; the only trace of\nthe original separation is in a slight constriction of the surface. The\nmovements of the caterpillar were few, simple, slow, and those of the\nbutterfly are many, varied, and rapid.\n\n20. In the Vertebrates the coalescence of ganglia is such that the\nspinal axis is one great centre. We do indeed anatomically and\nphysiologically subdivide it into several centres, because several\nportions directly innervate separate organs; but its importance lies in\nthe intimate blending of all parts, so that _fluctuating combinations_\nof its elements may arise, and varied movements result. Each centre\ncombines various muscles; the axis is a combination of centres. The\nbrainless frog, for instance, has still the spinal cord, and therefore\nthe power not only of moving either of his limbs, but also of combining\ntheir separate movements: if grasped, he struggles and escapes; if\npricked, he hops away. But these actions, although complex, are much\nless complex and varied than the actions of the normal frog.\n\nThere is not only a coalescence of ganglia, but a greater and greater\nconcentration of the substance in the upper portions of the axis. In\nthe inferior vertebrates, and in the mammalian embryo, the spinal\ncord occupies the whole length of the vertebral canal from the head\nto the tip of the tail; and here the centres of reflexion correspond\nwith the several segments. But as the cranial mass develops there is a\nwithdrawal of neural substance from the lower parts, and the centres of\nreflexion are then some way removed from the segments they innervate.\nIn the animal development there is even a greater and greater\npredominance of the upper portions, so that the brain and medulla\noblongata are of infinitely more importance than the spinal cord.\n\n21. Besides the central group of elements which belong to fixed and\ndefinite actions, we must conceive these elements capable of variable\ncombinations, like the pieces of colored glass in a kaleidoscope, which\nfall into new groups, each group having its definite though temporary\nform. The elements constitute really a continuous network of variable\nforms. It is to such combinations, and not to fixed circumscribed\nganglia, that we must refer the subordinate centres of the axis. We\nspeak of a centre for Respiration, a centre for Laughing, a centre for\nCrying, a centre for Coughing, and so on, with as much propriety as\nwe speak of a centre for Swallowing or for Walking. Not that in these\ncases there is a circumscribed mass of central substance set apart for\nthe innervation of the several muscles employed in these actions, and\nfor no other purpose. Each action demands a definite group of neural\nelements, as each geometric form in the kaleidoscope demands a definite\ngroup of pieces of glass; but these same pieces of glass will readily\nenter into other combinations; and in like manner the muscles active\nin Respiration are also active in Laughing, Coughing, etc., though\ndifferently innervated and co-ordinated.\n\n22. The physiological rank of a centre is therefore the expression of\nits power of fluctuating combination. The medulla oblongata is higher\nthan the medulla spinalis, because of its more varied combinations;\nthe cerebrum is higher than all, because it has no fixed and limited\ncombinations. It is the centre of centres, and as such the supreme\norgan.\n\n\n\n\nCHAPTER II.\n\nTHE FUNCTIONAL RELATIONS OF THE NERVOUS SYSTEM.\n\n\n23. The distinguishable parts of this system are the central axis, the\ncranial nerves, and the spinal nerves, with the chain of ganglia and\nnerves composing the Sympathetic. Let us briefly set down what is known\nof their special offices.\n\nMen very early discovered that the nerves were in some way ministrant\nto Sensation and Movement; a divided nerve always being accompanied\nby insensibility and immobility in the limb. Galen, observing that\nparalysis of movement sometimes occurred without insensibility,\nsuggested that there were two kinds of nerve; but no one was able to\nfurnish satisfactory evidence in support of this suggestion until early\nin the present century, when the experiments of Charles Bell, perfected\nby those of Majendie and M\u00fcller, placed the suggestion beyond dispute.\n\n[Illustration: Fig.\u00a012.--_Transverse sections of spinal cord (dorsal\nregion)._]\n\n24. Fig.\u00a012 is a _diagram_ (not a drawing of the actual aspect, which\nwould be hardly intelligible to readers unversed in such matters)\nrepresenting two transverse sections of the spinal cord just where the\nnerve-roots issue. The gray substance is somewhat in the form of a\nrude H, in the dorsal region, and of the expanded wings of a butterfly\nin the lumbar enlargements (Figs.\u00a04\u20136); the extremities of this gray\nsubstance are the _anterior and posterior horns_. We have already said\nthat from the anterior horns of each half issue the roots of the motor\nnerves, which pass to the muscles. From the posterior horns issue the\nsensory nerves, which, soon after leaving the cord, enter the ganglia\nbefore joining the motor nerves, and then pass to the skin, in the\nsame sheath with their companions, separating again as they reach the\nmuscles and surfaces where they are to be distributed. When this mixed\nnerve is cut through, or tied, all sensation and movement disappear\nfrom the parts innervated. But if only one of the roots be cut through,\nabove the ganglion, there will then be only a loss of movement or a\nloss of sensation. Thus suppose the section be made at _a_, _b_, A:\nwe have then divided a sensory nerve, and no pinching or pricking of\nthe part innervated by that nerve will be felt; but movement will take\nplace if the under nerve be irritated, or if a sensation _elsewhere_ be\nexcited. Now reverse the experiment, as at B, _c_, _d_. Then, pricking\nof the skin will be felt, but no movement will respond. The nerve which\nenters the cord at the upper (posterior) part is therefore a sensory\nnerve; that which enters at the under (anterior) part is motor. The\ndirection is in each case indicated by the arrow. The central end _b_,\nif irritated, will produce sensation; whereas the peripheral end _a_\nproduces neither sensation nor movement. The central end _d_ produces\nneither sensation nor movement; the peripheral end _c_ produces\nmovement.\n\n25. Two facts are proved by these experiments. First, that the\nco-operation of the centre is necessary for Sensation, but not for\nMovement. Although normally all the muscles of the trunk are moved only\nwhen their centre has been excited, yet any irritation applied directly\nto the muscle nerve, even when separated from its centre, produces a\nmovement. And to this we may add that a slighter stimulus will move the\nmuscle by direct irritation of the nerve, than by indirect irritation\nthrough the centre; a slighter stimulus also will suffice when applied\nto the nerve than when applied to the muscle itself.\n\n26. The second fact proved is known as _Bell\u2019s Law_, that the sensory\nand motor channels are respectively the posterior and anterior nerves.\nThe fact is indisputable, but its theoretic interpretation can no\nlonger be accepted in its original form. Bell supposed the two nerves\nto be different in kind, endowed with different specific energies, the\none sensitive, the other motor. The majority of writers still express\nthemselves as if they adopted this view. We shall, however, presently\nsee reason for replacing it by the more consistent interpretation\nwhich assigns one and the same property to both nerves, marking their\ndistinction by the terms afferent and efferent; the one set being\nanatomically so disposed that it conveys stimuli from the surfaces to\nthe centre, and the other set conveying stimuli from the centre to the\nmuscles, glands, and other cells.[89]\n\n27. Bell\u2019s discovery was rapidly generalized. The principle of\nlocalization was extended to all nerves, and of course to the posterior\nand anterior columns of the spinal cord, which indeed were assumed to\nbe continuations of the nerves. Bell, who was greater as an anatomist\nthan as a philosopher, always maintained that anatomical deduction was\nsuperior to experiment. But this was to misunderstand the reach of\ndeduction, which is only valid to the extent of its premises.[90] In\nthe present case, the premises assumed that the posterior columns were\ncontinuations of the posterior roots, and carried impressions to the\nbrain, the anterior columns carrying back from the brain the \u201cmandates\nof the will.\u201d Experiment has, however, decisively shown that it is\n_not_ through the posterior columns that sensory impressions travel to\nthe brain, but through the central gray substance.\n\n28. The spinal cord with its central gray substance is at each point\na centre of reflexion. Connected as it is with different organs, we\nartificially consider it as a chain of different centres, and try to\ndetect the functional relations of its parts. The inquiry is important,\nbut we must bear in mind the cardinal principle that diversity of\nFunction depends on the organs innervated, and not on a diversity of\nProperty in the nervous tissue. Although all nerves have a common\nstructure and common property, yet we distinguish them as sensory and\nmotor; and the sensory we subdivide into those of Special Sensation\nand those of Systemic Sensation. The motor we divide into muscular,\nvasomotor, and glandular. The hypothesis of specific energies must be\nrelinquished (\u00a7 63).\n\nIn like manner all centres have a common structure and a common\nproperty, with a great diversity of functional relations. Here also the\nhypothesis of specific energies has been generally adopted, owing to\na mistaken conception of the biological principle just mentioned. The\ncerebral hemispheres are credited with the properties of sensation,\nthought, and volition; the cerebellum with the property of muscular\nco-ordination; the spinal cord with the property of reflexion.\n\n29. No attempt to assign the true functional relations of the centres\nwill be made at the present stage of our exposition. We must learn more\nof the processes in Sensation, Thought, and Volition, before we can\nunravel the complex physiological web on which they depend. But here,\nprovisionally, may be set down what observation and experiment have\ndisclosed respecting the part played by certain centres. We know, for\nexample, that when the cerebral hemispheres are carefully removed from\na reptile or a bird, all the essentially _vital_ functions go on pretty\nmuch as before, but a great disturbance in some of the _psychical_\nfunctions is observed. The brainless bird eats, drinks, sleeps, moves\nits limbs separately and in combination, manifests sensibility to\nlight, sound, and touch, performs such instinctive actions as preening\nits feathers, or thrusting the head under the wing while roosting.\nThrow it into the air and it will fly. In its flight it will avoid\nobstacles, and will alight upon a ledge, or your shoulder. But it will\nnot fly unless thrown into the air; it will not escape through the\nopen door or window; it will avoid objects, but will show no fear of\nthem,--alighting on your head, for example, without hesitation. It is\nsensitive to light, and may in a certain sense be said to _see_; but\nit fails to _perceive_ what is _seen_. It will eat and drink, if food\nand water be administered, but it will starve near a heap of grain and\nnever peck it, not even if the beak be thrust into the heap. A grain,\nor strip of meat, may be thrust inside the beak; there it will remain\nunswallowed, unless it touches the back of the mouth, then swallowing\nat once follows the stimulus. The bird _with_ its brain will fly away\nif you turn the finger, or stick, on which it is perching; _without_\nits brain, it makes no attempt to fly, but flutters its wings, and\nbalances itself. If you open the mouth of a cat, or rabbit, and drop\nin some bitter fluid, the animal closes its mouth firmly, and resists\nyour efforts to repeat the act; without its brain, the animal shows the\nsame disgust at the taste, but never resists the preliminaries of the\nrepetition.\n\n30. These, and analogous facts, have been noted by various\nexperimenters. They are very far from proving what is usually\nconcluded; but they prove the important negative position that the\ncerebrum is not the centre of innervation for any of the organs on\nwhich the observed actions depend. Thus, the cerebrum is not necessary\nto sight: _ergo_ it does not innervate the eye. It is not necessary to\nhearing: _ergo_ it does not innervate the ear.[91] It is not necessary\nto breathing, swallowing, flying, etc.: _ergo_ it does not innervate\nthe organs of these functions.\n\nWhat then is lost? We have only to remember that the cerebrum is\ncontinuous with the thalami and corpora striata, and, through its\ncrura, with the medulla oblongata and medulla spinalis, to foresee\nthat its removal must more or less affect the whole neural axis,\nand consequently disturb the actions of the whole organism; this\ndisturbance will often have the appearances which would be due to the\nremoval of a central apparatus, so that we shall be apt to attribute\nthe cessation of a function to the loss of its organ, when in fact the\ncessation is due simply to an arrest of the organ by irritation. Thus\nthe cessation of consciousness, or of any particular movements, when\nthe cerebrum is removed, is no decisive proof that the cerebrum is the\norgan of consciousness, or of the movement in question. This point will\nbe duly considered hereafter. What we have now to consider is the facts\nobserved after removal of the cerebrum.\n\nFirst, we observe a loss of that power of combining present states\nwith past states, present feelings with feelings formerly excited in\nconjunction with them, the power which enables the animal to adjust\nits actions to certain sensations _now unfelt_ but which _will be_\nfelt in consequence of the adjustment. Secondly, we observe a loss of\nSpontaneity: the bird, naturally mobile and alert, now sits moveless\nfor hours in a sort of stupor, occasionally preening its feathers, but\nrarely quitting its resting-place. All the most conspicuous phenomena\nwhich we assign to Intelligence and Will seem absent. The sensations\nare altered and diminished. Many Instincts have disappeared, but some\nremain. The sexual feeling is preserved, although the bird has lost\nall power of directing its actions so as to gratify the desire. But\nthese effects are only observed when the whole of both hemispheres have\nbeen removed. If a small portion remain the bird retains most of its\nfaculties, though with less energy. In frogs and fishes there is little\ndiscernible effect observed when a large portion of the cerebrum is\nremoved.\n\n31. Now take away from this mutilated bird its cerebellum: all the\nfunctions continue as before except that _some_ combined movements can\nno longer be effected; flight is impossible; walking is a mere stagger.\nRemove only the lateral lobes, and though flight is still possible\ngreat _incoherence_ of the wings is observed, whereas walking is not\nmuch affected. If only the cerebellum be removed, the cerebrum being\nintact, the phenomena are very different. All the perceptions and\nalmost all the emotions, all the spontaneity and vivacity are retained;\nbut the sexual instinct, which was manifested when the cerebrum was\nremoved, is now quite gone. What we call Intelligence seems unaffected.\nThe bird hears, and understands the meaning of the sounds, sees and\nperceives, sees and fears, sees and adjusts its movements with a mental\nvision of unseen consequences.[92]\n\n32. Are we from these facts to conclude that the cerebrum is the \u201corgan\nof the mind\u201d; that it is \u201cthe seat\u201d of sensation, thought, emotion,\nvolition; and that the cerebellum is the \u201cseat\u201d of the sexual instinct,\nand muscular co-ordination? Such conclusions have found acceptance,\neven from physiologists who would have been startled had any one\nventured to affirm that the medulla oblongata was the \u201corgan\u201d of\nRespiration, because Respiration ceases when this centre is destroyed.\nI shall have to combat this notion at various stages of my exposition.\nHere let me simply say that it is irreconcilable with any clear\nconception of organ and function; and is plainly irreconcilable with\nany survey of psychical phenomena in animals in whom the cerebrum does\nnot exist, and in animals from whom it has been removed.\n\nWhat the facts indisputably prove is that the cerebrum has an important\npart in the mechanism by which the most complex psychical combinations\nare effected, and that the cerebellum has an important part in the\nmechanism by which the most complex muscular combinations are\neffected. The supreme importance of the cerebrum may be inferred from\nits dominating all the other centres, and from its preponderance in\nsize. In man it stands to all the other cranial centres together in\nthe relation of 11 to 3. It is about five times as heavy as the spinal\ncord--that is to say from 1,100 to 1,400 grammes, compared with 27 to\n30 grammes. The quantity of blood circulating through it is immense.\nHaller estimated the cranial circulation as one fifth of the whole\ncirculation. If, therefore, the Nervous Centres are agents in the\nproduction of Sensation and Intelligence, by far the largest share must\nbe allotted to the cranial centres, and of these the largest to the\nCerebrum.\n\n33. It is, however, one thing to recognize the Cerebrum as having\nan important part in the production of psychical phenomena, another\nthing to localize all the phenomena in it as their organ and seat--a\nlocalization which soon becomes even more absurd, when of all the\ncerebral structure the multipolar cells alone are admitted as the\nactive agents!\n\nAs was said just now, we recognize in the Medulla Oblongata the nervous\ncentre of Respiration, but we do not suppose that Respiration has its\n_seat_ there, nor that this centre is absolutely indispensable for\nthe essential part of the process. We respire by our skin, as well as\nby our lungs; many animals respire who have nothing like a medulla\noblongata; as many animals feel, and manifest will, who have nothing\nlike a cerebrum. The destruction of centres is of course a disturbance\nof the mechanisms which they regulate. But even the observed results\nof a destruction require very close examination, and are liable to\nerroneous interpretations. The disappearance of a function following\nthe destruction, or disease of a particular part, is not to be accepted\nas a proof that this part is the organ of the lost function; because\nprecisely the same phenomena may often be observed following the\ndestruction of a totally different part.[93] But one result may always\nbe relied on, and that is the _persistence_ of a function after removal\nof a particular part. Thus there is a certain spot of the cerebral\nconvolutions from which movements of the limbs are excited when the\nelectrodes are applied to it; removal of the substance is immediately\nfollowed by paralysis of the limbs. Are we to conclude that this spot\nis the organ of the function? It is true that the function is called\ninto action by a stimulus applied to this spot: true that the function\nsuddenly vanishes when the substance of this spot is destroyed.\nNevertheless, what seems a loss of function is only a disturbance. In\ntwo or three days the paralysis begins to disappear, and at the end\nof a week the limbs are moved nearly in the normal manner. And the\nsame is true when the spot in question is destroyed on both sides. The\nrecovery of the function shows that the absent part was not its organ.\nThere is a paradoxical experiment recorded by M. Paul Bert which may be\ncited here. He removed the right cerebral hemisphere from a chameleon,\nand found that the limbs on the left side were paralyzed; but on his\nthen removing the left cerebral hemisphere the limbs of the left side\nrecovered their activity. A similar result was obtained by Lussana and\nLemoigne by extirpation of the thalami. When we find combined movements\npersisting after the cerebellum has been destroyed, we may be sure that\nthe cerebellum is not the organ by which such combinations take place;\nand when we find sensation and volition manifested after the cerebrum\nhas been removed, we may be sure that the cerebrum is not the organ for\nthese sensations and volitions.\n\n34. And this we do find. Physiologists, indeed, for the most part,\ndeny it; or rather, while they admit the observed facts, they refuse\nto admit the only consistent interpretation, biassed as they are by\nthe traditional conception of the brain. After having for many years\npersistently denied Sensibility to any centre except the cerebrum, they\nare now generally agreed in including the medulla oblongata within the\nprivileged region; but they still exclude the medulla spinalis.\n\n35. If all the cranial centres as far as the medulla oblongata are\nremoved from young rabbits, dogs, or cats, there are unmistakable\nevidences of Sensibility in their _cries_ when their tails are pinched,\ntheir _moving jaws_ (as in mastication) when bitters are placed in\ntheir mouths, and their _raised paws rubbing their noses_, when\nirritating vapors are applied. It is said indeed that the cries are no\nsigns of _pain_; and this is probable; but they are assuredly signs of\nSensibility.\n\n35. The frog thus mutilated has lost indeed all its special senses,\nexcept Touch, but it still breathes, struggles when grasped, thrusts\naside the pincers which irritate it, or wipes away acid dropped on its\nskin. If the eye be lightly touched, the eyelid closes; if the touch\nbe repeated three or four times, the foreleg is raised to push the\nirritant away; if still repeated, the head is turned aside; but however\nprolonged the irritation, the frog neither hops, nor crawls away, as he\ndoes when the cerebellum remains. Place the brainless frog on his back,\nand if the medulla oblongata remains he will at once regain the normal\nposition; but if that part is absent he will lie helpless on his back.\nThe power of preserving equilibrium in difficult positions--which\nof course implies a nice co-ordination of muscles--resides in the\nso-called _optic lobes_ of the frog (what in mammals are called the\n_corpora quadrigemina_).\n\n37. With the destruction of each part of the central mass there will\nnecessarily be some disturbance of the mechanism; but difficult as\nmay be the task of detecting by experiment what is the normal action\nof any one part, there ought to be no hesitation in recognizing the\npersistence of functions after certain parts are destroyed. The\nspinal cord is anatomically known to be the centre from which the\nlimbs, trunk, and genito-urinary organs are innervated. So long as\nthe mechanism of the actions involving such organs is intact, no\nremoval of other parts will prevent this mechanism from exhibiting its\nnormal action. There may indeed arise, and there has arisen, the doubt\nwhether Sensibility is involved in the action of any nerve centre below\nthe medulla oblongata. But this doubt is founded on the traditional\nhypothesis respecting the seat of Sensation, and is flagrantly at\nvariance with the logical conclusions of Anatomy and Experiment.\n\n38. Anatomy shows that the structure of the spinal cord is in all\nessential characters the same as that of the medulla oblongata; and\nindeed that the whole central axis has one continuous tissue, somewhat\nvariously arranged, and in relation with various organs.\n\nAbundant Experiment has shown that the spinal cord, apart from the\nencephalon, is capable of acting as a sensorial and volitional centre.\nThe striking facts advanced by Pfl\u00fcger, Auerbach, and myself, have\nnot been impugned;[94] but their interpretation has been generally\nrejected. We showed that a brainless frog responded to stimulation in\nactions which bore so close a resemblance to actions admitted to be\nsensorial and volitional--showed the frog _adapting_ itself to new\nconditions, and _acquiring_ dexterity in executing actions which at\nfirst were impossible or difficult, _devising_ combinations to effect\na purpose which never by any possibility could have formed part of its\nhabits--manifesting, in a word, such signs of Sensibility, that no one\nwitnessing the experiments could hesitate as to the interpretation, had\nhe not been biassed by the traditions of the schools.\n\n39. Our opponents argued that in spite of all appearances there\nwere profound differences between the actions of the normal and the\nbrainless animal, and that the latter were due simply to Reflex Action.\nI also insist on profound differences; but underlying these there\nare fundamental identities. As to the Reflex Action, two points will\nhereafter be brought forward: 1\u00b0, that _all_ central action is reflex,\nthe cerebral no less than the spinal; 2\u00b0, that the hypothesis of Reflex\nAction being purely _mechanical_, and distinguished from Voluntary\nAction in not involving Sensibility, is an hypothesis which must be\nrelinquished.\n\n40. Postponing, however, all discussion of these points, let me here\nsay that the doctrine maintained in these pages is that the whole\ncerebro-spinal axis is a centre of Reflexion, its various segments\ntaking part in the performance of different kinds of combined action.\nIt has one common property, Sensibility; and different parts of it\nminister to different functions--the optic centre being different from\nthe auditory, the cerebral from the spinal; and so on. To make this\nintelligible, however, we must first learn what is known respecting the\nproperties of nerve-tissue.\n\n\n\n\nCHAPTER III.\n\nNEURILITY.\n\n\n41. Observation having found that the activity of a nerve was always\nfollowed by a sensation when the nerve ended in a centre, and by a\nmovement when the nerve ended in a muscle, Theory was called upon\nto disclose the nature of this peculiar property of nerves. That a\npeculiar and mysterious power did act in the nerves no one doubted;\nthe only doubt was as to its nature. The ancient hypothesis of Animal\nSpirits seemed all that was needed. The spirits coursed along the\nnerves, and obeyed the mandates of the Soul. When this hypothesis fell\ninto discredit, its place was successively taken by the hypotheses of\nNervous Fluid, Electricity, and Nerve Force. The Fluid, though never\nmanifested to Sense, was firmly believed in, even so late as the days\nof Cuvier;[95] but when the so-called electrical currents were detected\nin nerves, and the nervous phenomena were shown to resemble electrical\nphenomena, there was a general agreement in adopting the electrical\nhypothesis. The brain then took the place of a galvanic battery; the\nnerves were its electrodes.\n\n42. Closer comparison of the phenomena detected various irreconcilable\ndifferences, which, if they proved nothing else, proved that\nnerve-action took place under conditions so special as to demand a\nspecial designation. Electricity itself is so little understood, that\nuntil its nature is more precisely known, we cannot confidently say\nmore than that nerve-action resembles electrical-action; meanwhile the\nspeciality of neural conditions renders all deduction illusory which\nis based on electrical-action as observed under _other_ conditions.\nIn presence of these difficulties, cautious physiologists content\nthemselves with assigning the observed phenomena to the observed\nand inferred conditions, condensing these in the convenient symbol\n\u201cnerve-force,\u201d without pretending to any specification of the nature\nof that force. It may be a wave of molecular movement dependent on\nisometric change or on metamorphic change. It may be the liberation of\nmolecular tension resembling electricity; it may be electricity itself.\nBut whatever the nature of the change, it is an activity of the tissue,\nand as such comes under the general dynamic conception of Force or\nEnergy.\n\n43. In this sense the term has nothing equivocal or obscure.\nIt is a shorthand expression symbolizing certain well-defined\nobservations. Nevertheless, it is a term which we shall do well to\navoid when possible, and to replace by another having less danger of\nmisinterpretation; the reason being that Force has become a sort of\nshibboleth, and a will-o\u2019-wisp to speculative minds. All that we _know_\nof Force is Motion. But this is too meagre for metempirical thinkers,\nwho disdain the familiar experiences expressed in the term Motion,\nand demand a transcendent cause \u201cto account\u201d for what is observed.\nThey seek an entity to account for the fact. Motion is a very definite\nconception, expressing precise experiences; we know what it means, and\nknow that the laws of moving bodies admit of the nicest calculation.\nA similar precision belongs to Force when understood as \u201cmass\nacceleration,\u201d or M V\u00b2. But this does not content those metaphysicians\nwho understand by Force \u201cthe unknown reality behind the phenomena\u201d--the\n_cause_ of Motion. This cause they refuse to recognize in some\nantecedent motion (what I have termed a \u201cdifferential pressure\u201d), but\ndemand for it a physical or metaphysical _agent_: the physical agent\nbeing a subtle fluid of the nature of Ether, or a nerve atmosphere\nsurrounding the molecules; the metaphysical agent being a Spirit or\naggregate of Soul-atoms. The second alternative we may decline here\nto discuss. The first alternative is not only a pure fiction, but one\nwhich is inconsistent with the demonstrable velocity of the neural\nprocess, which is not greater than the pace of a greyhound, whereas\nthe velocities of light and electricity are enormously beyond this. It\nis inconsistent also with the observation that a much feebler current\nof electricity is requisite for the stimulation of a muscle through\nits nerve than when directly applied to the muscle: a proof that the\nnerve does not act solely by transmission of electricity--unless we\ngratuitously assume that the nerve is a multiplicator.\n\nWhen it is said that the living nerve is incessantly liberating Force\nwhich can be communicated to other tissues, the statement is acceptable\nonly if we reject the metaphysical conceptions it will too generally\nsuggest--the conceptions of Force as an entity, and of its being\npassed from one object to another like an arrow shot from a bow. The\nphysical interpretation simply says that the molecules of the nerve are\nincessantly vibrating, and with varying sweep; these vibrations, when\nof a certain energy, will set going vibrations in another substance by\ndisturbing the tension of its molecules, as the vibrations of heat will\ndisturb the tension of the gunpowder molecules, and set them sweeping\nwith greater energy: this is the _communication_ of the force. Just as\nwe say that a magnet communicates magnetic force to a bit of iron,\nthough all we mean is that the magnet has so altered the molecular\ncondition of the iron as to have given it the movements called\nmagnetism--in short, has excited in the iron the dormant property of\nbecoming magnetic--so we say the nerve communicates its force to the\nmuscle, exciting in the muscle its dormant property of contraction.\nBut in truth nothing has passed from magnet to iron, or from nerve to\nmuscle.\n\n44. Do what we will, however, there is always, in the present condition\nof philosophical chaos, the danger of being misunderstood when we\nemploy the term Nerve-force; and I have proposed the term Neurility as\nan escape from the misleading suggestions. It is a symbol expressing\nthe general property of nerve-tissue. For reasons presently to be\nstated, I restrict Neurility to the peripheral system, employing\nSensibility for the central system. The excited muscle manifests its\nspecial property of Contractility; the excited nerve manifests its\nspecial property of Neurility; the excited centre manifests its special\nproperty of Sensibility.[96] The terms are simply descriptive, and\ncarry with them no hypothesis as to _what_ Neurility is in its hidden\nprocess, nor _how_ Sensibility arises in a nerve-centre, and not\nelsewhere. We know that a stimulated muscle contracts, and we express\nthe fact by assigning to muscular tissue the property of Contractility.\nWe know that a stimulated nerve translates an impulse from one point to\nanother, and excites the muscle to contract; and we express the fact\nby assigning to nerve-tissue the property of transmitting stimulation,\nwhich is further specified, as unlike other transmissions, by the term\nNeurility.\n\n45. What is the meaning attached to the term Property, and how it is\ndistinguished from Function, has been already expounded in Problem\n1, \u00a7\u00a7 81\u20136. There also was laid down the principle of _identity of\nstructure implying identity of property_. Inasmuch as observation\nreveals a fundamental similarity in the structure of the nervous tissue\nthroughout the animal kingdom, we must conclude the existence of a\nfundamental similarity in the property of that tissue: a conclusion\nconfirmed by observation. There is a corresponding agreement in the\norgans and functions; so that, within certain limits, the experiments\nperformed on an insect may be verified on a mammal. Everywhere\nnerve-tissue has certain characters in common, accompanied by\nvariations in the degree and mode of manifestation corresponding with\nvariations in structure and connection. Obvious as the fact is, we\nmust emphasize the great variety which accompanies the underlying\nuniformity, for this is recognizable both in the individual organism\nand in the animal kingdom at large. Even such seemingly individual\nterms as nerve-cell and nerve-fibre are in truth generic; and the\ndescription which accurately represents one cell or fibre needs\nmodifying for others.\n\nProperties are generalized expressions; they result from the\n_composition_, the _structure_, and the _texture_ of a substance. Thus\none bar of iron may differ from another of equal bulk in being more or\nless crystalline in structure, though having the same composition and\nthe same texture. This difference will modify the mode of manifestation\nof the iron-properties. Cast-iron pillars, for example, will support,\nas a roof, a weight which would break them if suspended; wrought-iron\npillars of similar bulk will bear a weight suspended which would crush\nthem as a roof. Yet both cast and wrought iron pillars have the same\nproperties, because they have the _same_ composition and _similar_\nstructure; the variation of structure only producing a difference in\nthe modes. Texture may also vary. The bar of iron may be beaten into\na plate, rolled into a cylinder, or split into wire-work, without any\nchange in its properties, but with marked differences in its modes of\nmanifestation, and in the _uses_ to which it may be applied. These uses\nare of course dependent on the connections established between the iron\nand other things. In Physiology, _uses_ are called _functions_.\n\n46. Nerve-tissue must be understood as having everywhere the same\ngeneral Property. In one animal and in another, in one part and in\nanother, Neurility is the same in kind, but not everywhere manifesting\nthe same degree, nor applied to the same Function. The _composition_\nof nerve-tissue varies, but not more than the composition of all other\norganized substances; the _structure_ is variable, but only within\na small range; the _texture_ also; while the _connections_ are very\nvarious. Hence, whatever the variations in composition or structure,\nthe nerve-fibre has everywhere one fundamental property, which in\nconnection with a muscle has the functional activity of exciting\ncontraction; in connection with a gland of exciting secretion; and in\nconnection with a centre of exciting reflexion.[97]\n\n47. Had a clear idea of Function as dependent on connexion been present\nto their minds certain physiologists would hardly have raised the\nmirage of \u201cNerve-force,\u201d a mysterious entity endowed with \u201cspecific\nenergies,\u201d and capable of producing vital and psychical phenomena by\nan occult process; nor would others have been led to the monstrous\nhypothesis of particular nerve-cells being endowed with thought,\ninstinct, and volition. They would have sought an explanation of\nfunctions in the combined properties of the co-operant organs and\ntissues. They would not have endowed one nerve with Sensibility, and\nanother nerve of identical structure with Motility;[98] one nerve with\na motor property, and another with the opposite property of inhibition.\nThey would have seen that all nerves have the same _property_, but\ndifferent _uses_ when in different connexions.\n\n48. Throughout the animal kingdom we see movement following on\nstimulation. Stimulation may be defined the change of molecular\nequilibrium. The stimulation of a muscle is produced indirectly through\na change in the nerve, or directly through a change in the muscle\nitself. In the simplest organisms there is no trace of nerve-tissue;\nbut their substance manifests Irritability (or as it is often called\nSensibility); and a stimulus to one part is propagated throughout--the\nwhole body moves when touched. Even in Polypes, where there is the\nbeginning of a differentiation, the motion is slowly propagated from\none part to the rest. A single tentacle retracts when touched; but the\nmovement rarely ends there; it is slowly communicated from one tentacle\nto the other, and from them to the whole mass. Touching the body,\nhowever, will not, if the touch be slight, cause the tentacles to move;\nso that we see here a beginning of that principle of specialization\nwhich is so manifest in the higher organisms: the tentacles have\nbecome the specially sensitive parts. Ascending higher in the scale of\norganisms we find those which habitually move particular parts without\nat the same time necessarily moving the rest; and this independence\nof parts, accompanying a more perfect consensus, we find to be\ndeveloped _pari passu_ with a nervous system. An immense variety of\npart-movements, with varying combinations of such movements, is the\nphysiological expression of the more complex nervous system.\n\n48 _a_. Deferring what has to be said of Sensibility till the next\nchapter, we may here touch on its relation to Irritability, which is\noften used as its synonym. _Objectively_ it cannot be distinguished\nfrom Irritability, nor indeed from the most general phenomenon of\nreaction under stimulation; in this it is an universal property. But\n_subjectively_ it is distinguishable as a peculiar mode of reaction,\nonly known in nerve-tissues. While all tissues are irritable, and react\non being stimulated, each tissue has its special mode of reaction. The\nsecreting-cell reacts differently from the muscle-cell. The reaction\nof the nerve is the innervation of a centre or a muscle; the reaction\nof an innervated centre is sensation; of a muscle, contraction. There\nare three aspects of neural reaction: excitation, propagation of the\ndisturbance, and innervation. The first is expressed by irritability,\nthe second by conductibility, the third by sensibility; but these are\nonly artificial distinctions in the general phenomenon of transmitted\nexcitation. The nerve substance is specially distinguished by its\ninstability of molecular equilibrium; it undergoes chemical change\nwith a readiness comparable to that of explosive substances. Hence\nits facility of propagation of disturbance. There is irritability and\npropagation of disturbance in muscular tissue, notably evident in\nthe continuous tissue of the heart, intestines, and ureter; but the\npropagation is slow and diffusive; whereas in the nerve it is rapid,\nand restricted along a definite path. By this rapidity and restriction\nthe force of the impact is increased; and thus a slight stimulus\napplied to the nerve is capable of disturbing the state of the muscle.\n\n49. Thus while molecular movement is a fundamental condition of\nVitality, and is incessant throughout organized substance, the massive\nmovements of the organism, and the movements of particular parts, are\nthe _directed quantities_ of this molecular agitation. They are due\nto stimulation. We distinguish this from mechanical impulsion. It\nis a vital process involving molecular change; it is not simply the\n_communication_ of motion from without, but the _excitation_ of motion\nwithin. It is not like the blow which merely displaces an object, but\nlike the blow which disturbs its molecular equilibrium. The effect,\ntherefore, depends on this molecular condition: the blow which scatters\na heap of gunpowder will explode a fulminating salt, and this, in\nexploding, will excite the gunpowder to explode. The stimulus which\nis too feeble to excite contraction in a muscle will be powerful\nenough to excite the neurility of a nerve, and _that_ will excite the\ncontractility of the muscle. The nerve-force is simply neural stimulus.\nIt acts upon the other tissues as the nitrogenous salt upon the\ngunpowder.\n\nAlthough it is now common to speak of nerves as transmitting waves of\nmolecular motion, and to regard nerves as the passive medium for the\n\u201ctransference of force,\u201d whereby the force is thus made an abstract\nentity, we must always remember that such phrases are metaphors, and\nthat the truer expression will be not \u201ctransference of force,\u201d but the\n\u201cpropagation of excitation.\u201d I mean that it is not the _force_ of the\nimpact nor its _energy_ which a nerve transmits, it is the vibratory\nchange produced in the nerve by the impact, which excites another\nchange in the organ to which the nerve goes. We know by accurate\nmeasurements that the excitation of a nerve lasts much longer than the\n_stimulus_, a momentary impact producing an enduring agitation. We know\nalso that the excitation of a centre lasts longer than the muscular\ncontraction it has initiated. We know, moreover, that a nerve may be\ntotally incapable of conducting an external stimulus, yet quite capable\nof conducting a central stimulus; were it a passive conductor like a\nwire this would not be so.[99]\n\n50. The nerve is essentially an exciter of change, and thereby a\nregulator. A muscle in action does not appreciably determine action\nin any other (except in the comparatively rare cases of anastomosing\nmuscles); a secreting cell does not propagate its excitation to others.\nThe nerve, on the contrary, not only propagates its excitation, and\nawakens the activity of the muscle or gland with which it is connected,\nbut through the centre affects the whole organism--\n\n    \u201cEin Schlag tausend Verbindungen schl\u00e4gt.\u201d\n\nThus it is that stimulation which in the simpler organisms was diffused\nthroughout the protoplasm, has in the complex organisms become the\nspecialized property of a particular tissue.\n\n51. Two general facts of supreme importance must now be stated: One is\nthe law of stimulation--_every excitation pursues the path of least\nresistance_. The second is the condition of stimulation--_unlike\nmechanical impulsion, it acts only at insensible distances_.\n\n52. This means that although a nerve may be excited by any stimulus\nexternal to it which changes its molecular condition, no propagation of\nthat change (i.\u00a0e. no stimulation through the nerve) is possible except\nthrough continuity of substance. Mere physical contact suffices to\nexcite the nerve; but if there be an interruption of continuity in the\nnerve itself, no stimulus-wave passes across that line. Cut a nerve,\nand bring the divided surfaces once more into close contact, there will\nstill be such a solution of continuity as to arrest the stimulus-wave,\nmere physical contact not sufficing for the propagation. Whereas across\nthe cut ends of a divided nerve, even visibly separated, the electric\ncurrent easily passes. This necessity for the vital continuity of\ntissue in the propagation of stimulation must always be borne in mind.\nThe presence of a membrane, however delicate, or of any tissue having\na different molecular constitution, suffices to arrest or divert the\nwave. I conceive, therefore, that it is absolutely indispensable that\na nerve should terminate in and _blend_ with a muscle or a centre,\notherwise no stimulation of muscle or centre will take place through\nthe nerve.\n\n[Illustration: Fig.\u00a013.]\n\n53. The difference between excitation from contact and stimulation\nfrom continuity may be thus illustrated. In Fig.\u00a013 we see the legs\nof a frog attached to the spine by the lumbar nerves (_l_), and lying\non the muscles (_m_) of one leg is the nerve (_c_) of another frog\u2019s\nleg. Applying the electrodes to (_l_), the muscles (_m_) are violently\ncontracted; not only so, but their contraction excites the other nerve\n(_c_), and the leg attached to this nerve is thereby thrown into\ncontraction. This \u201csecondary contraction,\u201d as Dubois Reymond calls it,\nmight be supposed to be due to a diffusion of the electrical current;\nbut that it is due to a change in the muscles (_m_) is proved by\ndelicate experiments showing that the movements in the detached leg are\nof precisely the same kind as those in the legs directly stimulated.\nIf there is only a muscular shock in the one case, there is only a\nmuscular shock in the other; if there is tetanus in the one, there is\ntetanus in the other; if the muscles of the first leg are fatigued\nand respond slowly and feebly, the response of the second is slow and\nfeeble. Moreover, the secondary contraction may be produced by chemical\nor mechanical stimulus, as well as by the electrical.\n\n54. Although the contraction of a muscle is thus seen to be capable\nof exciting a nerve in contact with it, the reverse is not true: we\ncan produce no contraction in a muscle by exciting a nerve simply in\ncontact with the muscle, and not penetrating its tissue and terminating\nthere. Accordingly we always find a nerve when about to enter a muscle\nor a centre losing its _protecting_ envelopes; it gradually becomes\nidentified as a protoplasmic thread with the protoplasm of the muscle\nor the centre.\n\n55. Neurility, then, is the propagation of molecular change. Two\noffices are subserved by the nervous system, which may respectively be\ncalled Excitation--the disturbance of molecular _tension_ in tissues,\nand consequent liberation of their energies; and Co-ordination--the\ndirection of these several energies into combined actions. Thus, when\nthe muscle is in a given state of molecular tension, the stimulation of\nits nerve will change that state, causing it to contract if it be in\nrepose. But this stimulation, which will thus cause a contraction, will\nbe arrested, if at the same time a more powerful stimulation reaches\nthe antagonist muscle, or some distant centre: then the muscle only\n_tends_ to contract.\n\n\nORIGIN OF NERVE-FORCE.\n\n56. After this brief account of Neurility we may pass to the\nconsideration of its origin. Are we to understand that this property\nbelongs to the nerves themselves in the sense in which Contractility\nbelongs to the muscles? or are we to accept the teaching which assigns\nthe origin of \u201cnerve-force\u201d to the ganglia, and regards the nerves\nsimply as passive conductors of a force developed in the cells?\n\n57. It is now many years since I ventured to criticise the reigning\ndoctrine, and to urge the necessity Of consistently carrying out the\ndistinction between Property and Function. I called attention to the\npositive evidence which contradicted the idea of passive conduction;\nand pointed out the illusory nature of the favorite analogy, in which\nganglia were likened to batteries, and nerves to the conducting wires.\nBut the old image still exerts its empire; and writers are still\nfound speaking of the brain as a telegraphic bureau, the ganglia as\nstations, and the nerves as wires. In the cells of the gray substance\nthey place a constantly renewing reservoir of nerve-force. There the\nforce is elaborated, stored up, and from thence directed along the\nnerves. The sensory nerve \u201ctransmits an impression to the brain\u201d--as\nthe wire transmits a message to the bureau. The motor nerve, in turn,\n\u201ctransmits the mandates of the will\u201d--and all is clear! Clear, until\nwe come to translate metaphors into visible facts, or try to conjure\nup some mental image of the process. For myself, I can only conceive\nnerve-force as the activity of the nerve, and not of something\n_else_. This becomes still more evident when I find that the activity\nis equally manifest after its imaginary source has been removed.\nTransmitting impressions, or messages, implies as a preliminary that\nthere should be an impressible agent, or a _message-sender_, at the\nperiphery. No one supposes that simply touching one end of a wire\nwould send an \u201cimpression\u201d or a \u201cmessage\u201d to the battery; or that\nwithout the battery this touch would evolve a current. The battery is\nindispensable; in _it_ is evolved the current which the wire transmits.\nNot so the ganglion, or brain. Remove the wire from its connection with\nthe battery, and it is a bit of wire, nothing more. But remove a nerve\nfrom its connection with a ganglion, and it is still active as nerve,\nstill displays its Neurility when excited, still moves the muscle as\nbefore. The amputated limb will move when its nerves are stimulated,\njust as when a reflex from its centre moved it. Every one knew the\nfact; it was staring them in the face, yet they disregarded it. Even\nthe old anatomist, Willis, had recorded experiments which ought to have\nopened their eyes. He tied the phrenic nerve, and found that, when\nhe irritated it below the ligature, the diaphragm moved; but when he\nirritated it above the ligature, no movement followed. Since his days,\nthousands of experiments have shown that the presence of a ganglion is\nnot necessary to the action of a nerve.[100]\n\n58. Of course an explanation was ready. The nerve was said to have been\n\u201cendowed with force\u201d from its ganglion during their vital connection;\nand this force, stored up in the nerve, was disposable for some time\nafter separation from the ganglion. We need not pause to criticise this\nmisty conception of one part \u201cendowing\u201d another with force; the plain\nfacts afford the best answer. There seemed, indeed, a confirmation\nof the hypothesis in the fact that although the nerve separated from\nits ganglion was capable of excitation, yet after a few excitations\nit was exhausted, and ceased to stimulate the muscle. It seemed like\nthe piece of magnetized iron which would act as a temporary magnet,\nthough quickly losing this borrowed power. But the whole fabric\nfell--or ought to have fallen--when extended observation discovered\nthat this exhausted nerve would, if left in repose, _recover_ its\nlost power. A nerve preserves its excitability as long as it preserves\nits structural integrity, and recovers its power in recovering that\nintegrity. The length of time varies.[101] Gratiolet found the muscles\nin the leg of a tortoise, which had been amputated a week before,\ncontract when the nerves were irritated; and Schiff found the divided\nnerve of a winter frog excitable at the end of three weeks. Even\nafter all excitability has disappeared, it will reappear if arterial\nblood be injected; just as muscles which have already begun to assume\ncadaveric rigidity recover their contractility after transfusion. Nor\nis this all. The separated nerve finally degenerates, and loses all its\nstructural characters and physiological properties; yet under favorable\nconditions it will regenerate--recover its structures and properties;\nand this even apart from a centre, as Vulpian showed. Very noticeable\nis the fact that the force said to be produced in the centre, and only\n\u201cconveyed\u201d by the nerve, vanishes gradually from the centre to the\nperiphery, and recovers from the periphery to the centre--the part of\nthe nerve which is farthest from the centre being excitable when the\npart nearest the centre is still inexcitable. Again, when a nerve is\npinched, contraction in the muscle follows; but the pinch has for a\ntime so disturbed the structural integrity of the nerve (at that spot)\nthat no irritant applied to the spot, or _between_ it and the centre,\nwill be followed by contraction, whereas _below_ the spot an irritation\ntakes effect. This is another form of the experiment of Willis. Even in\nits normal state, the nerve has different degrees of excitability in\ndifferent parts of its course,--a fact discovered by Pfl\u00fcger which is\nquite irreconcilable with the hypothesis of passive conduction. Doubts\nhave been thrown on Pfl\u00fcger\u2019s interpretation,[102] namely, that there\nis an avalanche-like accumulation of energy proportionate to the length\nof the stimulated portion; but the fact remains, that one and the\nsame irritant applied successively to two different points of a nerve\ndoes not irritate the muscle in the same degree. Munk also finds the\nvelocity of transmission in a motor nerve increases as it approaches\nits termination in the muscle.[103]\n\n59. Nothing can be more unlike the conduction of an electric current\nthan this excitation of Neurility; nothing more accordant with the\nidea of it as a vital property of the tissue. The notion of its being\nderived from a centre is on a par with the notion first successfully\ncombated by Haller,[104] that the muscle derived its Contractility\nfrom the nerves; or the analogous notion that the electric organ\nin fishes derived its property from the brain. Indeed, it was in\nsupport of the hypothesis that the brain was a battery, and nerves\nthe conductors, that the phenomena observed in electrical fishes were\nfrequently cited. The electric organ was seen to be connected with\nthe brain; its discharges were under the control of the animal, and\nwere destroyed on one side when the brain on the corresponding side\nwas destroyed. But Charles Robin long ago suggested, what indeed ought\nnever to have been doubted, that the brain was not the source of the\nelectricity; but that the tissue of the electric organ itself had this\nspecial property, which the nerve merely called into activity. The\nsuggestion has been experimentally verified by M. Moreau, who divided\nall the nerves supplying the electric organ on one side, and, having\nthus cut off all communication with the brain, produced electrical\ndischarges by irritating the nerves; precisely as the muscles are made\nto contract when the divided nerves are irritated. Had the experiment\nceased here, it might have been interpreted on the old hypothesis: the\nelectric organ might be supposed to have a certain amount of electric\nforce condensed in it, stored up there, as it is said to be in the\nnerves, and discharged when the organ is irritated. But experiment has\ndecided this point also. Electric fishes notoriously exhaust their\npower by a few discharges, and recover it after repose. When M. Moreau\nhad exhausted his mutilated fishes, he replaced them in the water,\nand allowed them repose. On again irritating the divided nerves, the\ndischarges were again produced.[105]\n\n60. On all sides the idea of nerves deriving their power from another\nsource than their own substance is seen to be untenable. _A priori_\nthis might have been concluded. Neurility is the vital property of\nnerve-tissue. \u201cNerve-force\u201d is nerve-action--molecular changes in the\nnerve itself, not in some remote substance. That nerve and centre are\nvitally connected is true; and what their physiological relations are\nwill hereafter be examined; but we must dismiss the idea of nerves\nhaving the relation to centres that electrodes have to batteries.\n\n61. In proposing the term Neurility, I not only wished to get rid of\nthe ambiguities which hovered round \u201cnerve-force\u201d and \u201cnerve-current,\u201d\nbut to recall the physiological principle that properties are\ndependent on structures; and therefore that the special property of\nnerve-tissue is conditioned by its structure. Neurility is, of course,\nan abstraction; but so is _the_ nerve an abstraction. The concrete\nmanifestations are the several nerve-actions. These we classify and\nspecify. One class we call sensory, another class motor; not because\nthe nerve-action itself is different, but because it is in each class\nin a different functional relation to other parts. In classing men\nas governors and governed, employers and employed, we do not suppose\nanthropological distinctions, but only differences in their social\nfunctions.\n\n62. This is the modification of the Law of Bell to which reference was\nmade in \u00a7 26. It replaces the idea of two different kinds of nerve,\nsensory and motor, by that of two different anatomical connections. I\nneed not reproduce here the argument with which I formerly criticised\nthe supposed distinction between sensory and motor nerves; because\nthe old idea is rapidly falling into discredit, and physiologists so\neminent as Vulpian and Wundt have explicitly announced their adhesion\nto the principle of identity,--a principle which, as Vulpian truly\nremarks, dominates the whole physiology of the nervous system.[106]\n\n\nTHE HYPOTHESIS OF SPECIFIC ENERGIES.\n\n63. One development of the theory of Bell, respecting the different\nkinds of nerve, has been the still accredited hypothesis that each\nnerve has a \u201cspecific energy,\u201d or quality, in virtue of which it\nacts and reacts only in one way. The optic nerve, no matter how\nstimulated, only responds by a sensation of color, the auditory nerve\nonly by a sensation of sound; and so on. This hypothesis, which (as\nI learn from a correspondent)[107] was originally propounded by Bell\nhimself, was developed and made an European doctrine by Johannes\nM\u00fcller, first in his remarkable treatise, _\u00dcber die phantastischen\nGesichtserscheinungen_ (1826), and afterwards in his _Physiology_.\nLike all good hypotheses, it has been fruitful; and Helmholtz\nstill holds it to be of extraordinary importance for the theory of\nperception. Although combated by a few physiologists, it has kept its\nplace firm in the general acceptance; no doubt because it forms a ready\nexplanation of the facts. But, as I often have to remark, _explanation_\nis not _demonstration_.[108]\n\n64. The first criticism to be made on the hypothesis is that it\ncommits the error of confounding function with property, assigning as\na specific quality of the nerve the reaction of the organ innervated.\nThus M\u00fcller speaks of the specific energy as \u201cthe essential condition\nof the nerves in virtue of which they see light and hear sound.\u201d\nBut the optic nerve no more _sees_, than the liver-nerve _secretes_\nbile. That the optic nerve is one element in the mechanism on which\nvision depends, is all that we can say, M\u00fcller declares that it is\nnot sufficient to assume each nerve to be so constituted that it\nhas a susceptibility to certain stimuli rather than to others; but\nthat \u201cwith Aristotle we must ascribe to each a peculiar energy as\nits vital quality. Sensation,\u201d he adds, \u201cconsists in the sensorium\nreceiving through the medium of the nerves a _knowledge of certain\nqualities_,--a condition, not of the external bodies, but of the\nnerves themselves,\u201d--and these qualities are different in different\nnerves. In other words, he assumes a special substance for each special\nenergy. The sensation of color depends on the special Visual substance\n(_Sehsinnsubstanz_); the sensation of sound on the Auditory substance\n(_H\u00f6rsinnsubstanz_); and so on.\n\n65. We have here an hypothesis analogous to that of Innate Ideas, or\n_a priori_ Forms of Thought. It is, in fact, only a reproduction of\nthat conception carried into the sphere of Sense. No one thinks of\nassigning specific energies to the several muscles, yet a movement of\nprehension is as different from a movement of extension, a peristaltic\nmovement is as different from a movement of occlusion, as a sensation\nof sound is from a sensation of color. If movement is common to both\nof the one class, feeling is common to both of the other: the forms\nand mechanism are different and specific. Muscles have the common\nproperty of contracting under stimulation; whatever be the nature of\nthe stimulus, each muscle has its own particular response, or mode of\nreaction: the flexor always bending, never extending the limb; the\nsphincter always closing, never opening the orifice. The movements\nof the heart are not the same as those of the eye; both are unlike\nthe movements of the intestine. There are muscles which respond to\nsome stimuli, and not to others. Those of the eye, or of the vocal\nchords, respond to impulses which would leave the masseter or biceps\nunstirred. According to Marey, the hyoglossus of a frog will become\ntetanic under a stimulus of only ten pulses in a second; whereas the\ngastrocnemius of that same frog resists a stimulus of less than twenty\nin a second. We find the retina responding to ethereal pulses which\nleave the auditorius unaffected; we find the muscles of a gnat\u2019s wing\nso exquisitely susceptible that the wing beats eight thousand times in\na second,--a delicacy in comparison with which even our muscles of the\neye are coarse.\n\n66. The facts which the hypothesis of specific energies is called\non to explain are more consistently interpreted on the admission of\na common property in nerve-tissue, manifesting different degrees of\nexcitability, and entering into different mechanisms, so that the\nfunctional results differ. A nerve which may be stimulated from the\nskin will not respond at all, or not in the same way, if the stimulus\nbe applied under the skin. Are we to suppose that the specific energy\nresides in one part of the nerve, and not in another?[109] That the\noptic nerve responds to stimuli which will not sensibly excite a\nmotor nerve, depends on the terminal structures through which the\nstimulation is excited; for the optic nerve itself, apart from the\nretinal expansion, is as insensible to light as the motor nerve is. And\nthe specific sensation, or movement, which _results_ from stimulation\nof a nerve depends not on the nerve, but on the mechanism of which the\nnerve is one element. Sensations of touch, temperature, and pain are\nassuredly specific; they are as unlike each other as a sensation of\ntaste is unlike a sensation of smell. Yet the same nerves, variously\nstimulated, produce all three sensations.\n\n67. We conclude, therefore, that the phrase \u201cspecific energy\u201d is an\nelliptical expression for the particular office of a nerve. In this\nmeaning there is no obscurity. The optic nerve is not a vasomotor\nnerve, the skin nerve is not a muscle nerve; the auditory nerve is a\nnerve of special sensation, the vagus is a nerve of systemic sensation;\nand so on. Neither movement nor sensation belongs to the nerves\nthemselves.\n\n\n\n\nCHAPTER IV.\n\nSENSIBILITY.\n\n\n68. The principles laid down in the preceding chapter are equally\napplicable to the central system. But here greater difficulties await\nus. We cannot expect traditional views to be easily displaced, when\nthey have taken such hold on the mind, as is the case with regard to\nSensibility. To admit that all nerves have a common property, and that\ntheir functional relations depend on the organs which they innervate,\ndemands small relinquishment of cherished opinions. But to admit that\nall nerve-centres have a common property, and that their functional\nrelations depend on their anatomical connections, is to sweep away at\nonce a mass of theoretic interpretations which from long familiarity\nhave acquired an almost axiomatic force. That the brain, and the brain\nonly, is the source and seat of Sensibility is the postulate of modern\nPhysiology.\n\n69. The question is one of extreme complexity, but may be greatly\nsimplified, if we can manage to reduce it to purely physiological\nterms, and consider the phenomena in their objective aspect. In dealing\nwith nerves and their actions this was comparatively easy; we had for\nthe most part only physiological processes to unravel. It is otherwise\nin dealing with nerve-centres--the subjective or psychological aspect\nof the phenomena inevitably thrusts itself on our attention; and all\nthe mysteries of Feeling and Thought cloud our vision of the neural\nprocess. Do what we will, we cannot altogether divest Sensibility of\nits psychological connotations, cannot help interpreting it in terms\nof Consciousness; so that even when treating of sensitive phenomena\nobserved in molluscs and insects, we always imagine these more or less\nsuffused with Feeling, as this is known in our own conscious states.\n\n70. Feeling is recognized as in some way or other bound up with\nneural processes; but Physiology proper has only to concern itself\nwith the processes; and the question whether these can, and do, go on\nunaccompanied by Feeling, is, strictly speaking, one which belongs\nto Psychology. It demands as a preliminary that the term Feeling be\ndefined; and the answer will depend upon that definition, namely,\nwhether Feeling be interpreted as synonymous with Consciousness in the\nrestricted sense, or synonymous with the more general term Sentience.\nIf the former, then since there are unquestionably neural processes of\nwhich we are not conscious, we must specify the particular groups which\nsubserve Feeling; as we specify the particular groups which subserve\nthe sensations of Sight, Hearing, Taste, etc.; and localize the\nseparate functions in separate organs. If the latter, then, since all\nneural processes have a common character, we have only to localize the\nparticular variations of its manifestation, and distinguish sensitive\nphenomena as we distinguish motor phenomena.\n\n71. It is absolutely certain that the Feeling we attribute to a\nmollusc is different from that which we attribute to a man; if only\nbecause the organisms of the two are so widely different, and have\nbeen under such different conditions of excitation. If every feeling\nis the functional result of special organic activities, varying with\nthe co-operant elements, we can have no more warrant for assuming the\nexistence of the same _particular_ forms of Feeling in organisms\nthat are unlike, than for assuming the 47th proposition of Euclid to\nbe presented by any three straight lines. The lines are the necessary\nbasis for the construction, but they are not the triangle, except when\nin a special configuration. This is not denying that animals _feel_\n(in the general sense of that term), it is only asserting that their\nfeelings must be very _unlike_ our own. Even in our own race we see\nmarked differences--some modes of feeling being absolutely denied to\nindividuals only slightly differing from their fellows. If, however,\nwe admit that different animals must have different modes of Feeling,\nwe must also admit that the neuro-muscular activities are generically\nalike in all, because of the fundamental similarity in the structures.\nWhether we shall assign Feeling to the mollusc or not will depend on\nthe meaning of the term; but, at all events, we require some term\ngeneral enough to include the phenomena manifested by the mollusc,\nand those manifested by all other animals. Sensibility is the least\nobjectionable term. Unless we adopt some such general designation,\nphysiological and psychological interpretations become contradictory\nand obscure. The current doctrine which assigns Sensibility to the\nbrain, denying it to all other centres, is seriously defective,\ninasmuch as it implies that tissues similar in kind have utterly\ndiverse properties; in other words, that the same nerve-tissue which\nmanifests Sensibility in the brain has no such property in the spinal\ncord.\n\n72. How is this tenable? No one acquainted at first hand with the facts\ndenies that the objective phenomena exhibited by the brainless animal\nhave the same general character as those of the animal possessing a\nbrain: the actions of the two are identical in all cases which admit\nof comparison. That is to say, the objective appearances are the\nsame; differing only in so far as the mechanisms are made different\nby the presence or absence of certain parts. The brain not being a\nnecessary part of the mechanical adjustments in swimming, or pushing\naside an irritating object, the brainless frog swims and defends itself\nin the same way as the normal frog. But no sooner do we pass from\nthe objective interpretation, and introduce the subjective element\nof Feeling among the series of factors necessary to the product--no\nsooner do we ask whether the brainless frog _feels_ the irritation\nagainst which it struggles, or _wills_ the movements by which it\nswims--than the question has shifted its ground, and has passed from\nPhysiology to Psychology. The appeal is no longer made to Observation,\nbut to Interpretation. Observation tells us here nothing directly\nof Feeling. What it does tell us, however, is the identity of the\nobjective phenomena; and Physiology demands that a common term be\nemployed to designate the character common to the varied phenomena.\nSensibility is such a term. But most modern physiologists, under the\nbias of tradition, refuse to extend Sensibility to the spinal cord,\nin spite of the evidences of the spinal cord possessing that property\nin common with the brain. They prefer to invoke a new property; they\nassign spinal action to a Reflex Mechanism which has nothing of the\ncharacter of Sensibility, because they have identified Sensibility with\nConsciousness, and have restricted Consciousness to a special group of\nsensitive phenomena.\n\n73. Nor is it to be denied that on this ground they have a firm basis.\nEvery one could testify to the fact that many processes normally\ngo on without being accompanied by consciousness, in the special\nmeaning of the term. Reflex actions,--such as winking, breathing,\nswallowing,--notoriously produced by stimulation of sensitive surfaces,\ntake place without our \u201cfeeling\u201d them, or being \u201cconscious\u201d of them.\nHence it is concluded that the Reflex mechanism suffices without the\nintervention of Sensibility. I altogether dispute the conclusion; and\nin a future Problem will endeavor to show that Sensibility is necessary\nto Reflex Action. But without awaiting that exposition we may at once\nconfront the evidence, by adducing the familiar fact that \u201cunconscious\u201d\nprocesses go on in the brain as well as in the spinal cord; and this\nnot simply in the sphere of Volition, but also in the sphere of\nThought.[110] We act and think \u201cautomatically\u201d at times, and are quite\n\u201cunconscious\u201d of what we are doing, or of the data we are logically\ngrouping. We often think as unconsciously as we breathe; although from\ntime to time we become conscious of both processes. Yet who will assert\nthat these unconscious processes were independent of Sensibility?\nWho will maintain that because cerebral processes are sometimes\nunaccompanied by that peculiar state named Consciousness, therefore all\nits processes are unaccompanied by Feeling? And if here we admit that\nthe Reflex mechanism in the brain is a _sensitive_ mechanism, surely we\nmust equally admit that the similar Reflex mechanism in the spinal cord\nis sensitive?\n\n74. Let it be understood that Sensibility is the common property of\nnerve-centres, and physiological interpretations will become clear\nand consistent. Consciousness, as understood by psychologists, is not\na property of tissue, it is a function of the organism, dependent\nindeed on Sensibility, but not convertible with it. There is a greater\ndistinction between the two than between Sensation, the reaction of\na sensory organ, and Perception, the combined result of sensory and\ncerebral reactions; or than that between Contractility, the property of\nthe muscles, and Flying, the function of a particular group of muscles.\nIt is not possible to have Consciousness without Sensibility; but\nperfectly possible to have Sensations without Consciousness. This will\nperhaps seem as inconceivable to the reader as it seemed to Schr\u00f6der\nvan der Kolk.[111]\n\n75. Let us illustrate it by the analogy of Pain. There is a vast amount\nof sensation normally excited which is totally unaccompanied by the\nfeelings classed as painful. The action of the special senses may be\nexaggerated to an intolerable degree, but the exaggeration never passes\ninto pain: the retina may be blinded with excess of light, and the ear\nstunned with sound--the optic nerve may be pricked or cut--but no pain\nresults. The systemic sensations also are habitually painless, though\nthey pass into pain in abnormal states. Clearly, then, Pain is not the\nnecessary consequence of Sensibility; and this is true not only of\ncertain sensitive parts, but of all; as is proved in the well-known\nfacts of Analgesia, in which complete insensibility of the skin as\nregards Pain co-exists with vivid sensibility as regards Touch and\nTemperature. Hence the majority of physiologists refuse to acknowledge\nthat the struggles and cries of an animal, after removal of the brain,\nare evidences of pain; maintaining that they are \u201csimply reflex\nactions.\u201d This is probable; the more so as we know the struggles and\ncries which tickling will produce, yet no pain accompanies tickling.\nBut if the struggles and cries are not evidence of pain, they are\nsurely evidence of Sensibility.\n\n76. Now for the term Pain in the foregoing paragraph substitute the\nterm Consciousness, and you will perhaps allow that while it may be\njustifiable to interpret the actions of a brainless animal as due to a\nmechanism which is unaccompanied by the _specially conditioned forms_\nof Sensibility classed under Consciousness--just as it is unaccompanied\nby the specially conditioned forms of Perception and Emotion--there\nis no justification for assuming the mechanism not to have been a\n_sensitive_ mechanism. The wingless bird cannot manifest any Of the\nphenomena of flight; but we do not therefore deny that its _other_\nmovements depend on Contractility.\n\n77. Difficult as it must be to keep the physiological question apart\nfrom the psychological when treating of Sensibility, we shall never\nsucceed in our analysis unless the two questions are separately\ntreated. The physiologist considers organisms and their actions\nfrom their objective side, and tries to detect the mechanism of the\nobserved phenomena. These he has to interpret in terms of Matter and\nMotion. The psychologist interprets them in terms of Feeling. The\nactions which we _see_ in others we cannot _feel_, except as visual\nsensations; the changes which we feel in ourselves we cannot see in\nothers, except as bodily movements. The reaction of a sensory organ is\nby the physiologist called a sensation,--borrowing the term from the\npsychologist; he explains it as due to the stimulus which changes the\nmolecular condition of the organ; and this changed condition, besides\nbeing seen to be followed by a muscular movement, is _inferred_ to\nbe accompanied by a change of Feeling. The psychologist has direct\nknowledge only of the change of Feeling which follows on some other\nchange; he infers that it is originated by the action of some external\ncause, and infers that a neural process precedes, or accompanies, the\nfeeling. Obviously there are two distinct questions here, involving\ndistinct methods. The physiologist is compelled to complete his\nobjective observations by subjective suggestions; compelled to add\nFeeling to the terms of Matter and Motion, in spite of the radical\ndiversity of their aspects. The psychologist also is compelled to\ncomplete his subjective observations by objective interpretations,\nlinking the internal changes to the external changes. A complete theory\nmust harmonize the two procedures.\n\n78. In a subsequent Problem we shall have to examine the nature of\nSensation in its psychological aspect; here we have first to describe\nits physiological aspect. To the psychologist, a sensation is simply a\nfact of Consciousness; he has nothing whatever to do with the neural\nprocess, which the physiologist considers to be the physical basis\nof this fact; and he therefore regards the physiologists as talking\nnonsense when they talk of \u201cunconscious sensations,\u201d the phrase being\nto him equivalent to \u201cunfelt feelings,\u201d or \u201cinvisible light.\u201d It is\nquite otherwise with the physiologist, who viewing a sensation solely\nas a neural process, the reaction of a sensory organ, can lawfully\nspeak of unconscious sensations, as the physicist can speak of\ninvisible rays of light,--meaning those rays which are of a different\norder of undulation from the visible rays, and which may become visible\nwhen the susceptibility of the retina is exalted. He knows that there\nare different modes, and different complexities of neural process; to\none class he assigns consciousness, to the other unconsciousness. If he\nwould be severely precise, he would never speak of sensation at all,\nbut only of sensory reaction. But such precision would be pedantic and\nidle. He wants the connotations of the term sensation, and therefore\nuses it.\n\n79. The functional activity of a gland is stimulated by a neural\nprocess reflected from a centre; by a similar process a muscle is\ncalled into action. No one supposes that the neural process is, in\nthe one case secretory, in the other motory: in both it is the same\nprocess in the nerve; and our investigation of it would be greatly\nhampered if we did not disengage it from all the suggestions hovering\naround the ideas of secretion and muscular action. In like manner\nwe must disengage the neural process of a sensory reaction from all\nthe suggestions hovering around the idea of Consciousness, when that\nterm designates a complex of many reactions. In Problem III. we shall\nenter more particularly into the distinction between Sensibility and\nConsciousness; for the present it must suffice to say that great\nambiguity exists in the current usage of these terms. Sometimes\nConsciousness stands as the equivalent of Sensibility; sometimes as a\nparticular _mode_ of Sensibility known as Reflection, Attention, and\nThought. The former meaning is an extension of the term similar to\nthat given to the word Rose, which originally meaning Red came to be\nrestricted to a particular red flower; and after other flowers of the\nsame kind were discovered which had yellow and white petals, instead\nof red, the term rose still adhered even to these. \u201cYellow Rose\u201d is\ntherefore as great a verbal solecism as unconscious sensation. We have\nseparated the redness from the rose, and can then say that the color\nis one thing, the flower another. By a similar process of abstraction\nwe separate Consciousness from Sensation, and we can then say that\nthere are sensations without consciousness. In consequence of this,\npsychologists often maintain that to have a sensation and be conscious\nof it are two different states. We are said to hear a sound, and yet\nnot to be conscious of hearing it. The sound excites a movement, but\nit does not excite our consciousness. Now although it is true that\nthere are roses which are not red, it is not true that there are\nroses which have no color at all. Although it is true that there are\nsensations which are not of the particular mode of Sensibility which\npsychologists specially designate as Consciousness, it is not true\nthat there are sensations which are not modes of Sensibility.\n\n80. And what is Sensibility which, on its subjective side, is\nSentience? In one sense it may be answered that we do not know. In\nanother sense it is that which we know most clearly and positively:\nSentience forms the substance of all knowledge. Being the ultimate of\nknowledge, every effort must be vain which attempts to explain it by\nreduction to simpler elements. The human mind, impatient of ultimates,\nis always striving to pierce beyond the fundamental mysteries; and this\nimpatience leads to the attempts so often made to explain Sensibility\nby reducing it to terms of Matter and Motion. But inasmuch as a clear\nanalysis of Matter and Motion displays that our knowledge of these is\nsimply a knowledge of modes of Feeling, the reduction of Sentience or\nSensibility to Matter and Motion is simply the reduction of Sensibility\nto some of its modes. This point gained, a clear conception of the\nadvantages of introducing the ideas of Matter and Motion will result.\nIt will then be the familiar and indispensable method of explaining\nthe little known by the better known. The objective aspect of things\nis commonly represented in the visible and palpable; because what we\ncan see we can also generally touch, and what we can touch we can\ntaste and smell; but we cannot touch an odor nor a sound; we cannot\nsee them; we can only connect the odorous and sonorous objects with\nvisible or palpable conditions. Everywhere we find sensations referred\nto visible or palpable causes; and hence the desire to find this\nobjective basis for every change in Sensibility. The sensation, or\nstate of consciousness, is the ultimate fact; we can only _explain_ it\nby describing its objective conditions.\n\n81. Thus much on the philosophical side. Returning to our physiological\npoint, we must say that a sensation is, objectively, the reaction\nof a sensory organ, or organism; subjectively, a change of feeling.\nObjectively it is a phenomenon of movement, but distinguishable\nfrom other phenomena by the speciality of its conditions. It is a\nvital phenomenon, not a purely mechanical phenomenon. Although the\nmolecular movement conforms, of course, to mechanical principles, and\nmay be viewed abstractly as a purely mechanical result, yet, because\nit takes place under conditions never found in machines, it has\ncharacters which markedly separate it from the movements of machines.\nAmong these differential characters may be cited that of _selective\nadaptation_,[112] which is most conspicuous in volition.\n\n82. In the early stages of animal evolution there is no differentiation\ninto muscle and nerve. The whole organism is equally sensitive (or\nirritable) in every part. Muscles appear, and then they are the most\nsensitive parts. Nerves appear, and the seat of Sensibility has\nbeen transferred to them; not that the muscles have lost theirs, but\ntheir irritability is now represented by their dominant character of\nContractility, and the nerves have taken on the special office of\nSensibility. That is to say, while both muscle and nerve form integral\nelements of the sensitive reaction, the process itself is analytically\nconceived as a combination of two distinct properties, resident in two\ndistinct tissues.\n\n83. Carrying further this analytical artifice, I propose to distinguish\nthe central organs as the seat of Sensibility, confining Neurility to\nthe peripheral nerves. In physiological reality both systems, central\nand peripheral, are one; the separation is artificial. Strictly\nspeaking, therefore, Neurility--or nerve-action--is the general\nproperty of nerve-tissue, central and peripheral. But since Neurility\nmay be manifested by nerves apart from centres, whereas Sensibility\ndemands the co-operation of both, and since we have often to consider\nthe central process in itself, without attending to the process in the\nnerves, it is well to have two characteristic terms. I shall therefore\nalways use the term Sensibility for the reactions of the nervous\ncentres,--Sentience being its psychological equivalent; although the\nreader will understand that in point of fact there is no break, nor\ntransformation, as the wave of change passes from sensory nerve to\ncentre, and from centre to motor nerve: there is one continuous process\nof change. But just as we analytically distinguish the sensory from\nthe motor element of this indissoluble process, so we may distinguish\nthe ingoing and outgoing stages from the combining stage. Sensibility,\nthen, represents the property of _combining_ and grouping stimulations.\n\n84. Fully aware of the misleading connotations of the term, and of the\ndifficulty which will be felt in disengaging it from these, especially\nin reference to Consciousness, I have long hesitated before adopting\nit. But the advantages greatly outweigh the disadvantages. Sensibility\nhas long been admitted to express the peculiar modes of reaction in\nplants and animals low down in the scale. No one hesitates to speak of\na sensitive plant, or a sensitive surface. The tentacles of a polype\nare said to be sensitive; though probably no one thereby means that\nthe polype has what psychologists mean by Consciousness. By employing\nthe general term Sensibility to designate the whole range of reactions\npeculiar to the nerve-centres, when these special organs exist, it\nwill be possible to interpret all the physiological and psychological\nphenomena observed in animals and men on one uniform method. The\nobserved variations will then be referable to varieties in organisms.\n\n85. Suppose, for illustration, an organism like the human except\nthat it is wholly deficient in Sight, Hearing, Taste, and Smell. It\nhas no sense but Touch--or the general reaction under contact with\nexternal objects. It will move on being stimulated, and will combine\nits movements differently under different stimulations. It will feel,\nand logically combine its feelings. But its mass of feeling will be\nmade of far simpler elements than ours; its combinations fewer; and\nthe contents of its Consciousness so very different from ours that\nwe are unable to conceive what it will be like; we can only be sure\nthat it will _not_ be very like our own. This truncated Organism will\nhave its Sensibility; and we must assign this property to its central\nnerve-tissue, as we assign our own. If now we descend lower, and\nsuppose an organism with no centres whatever, but which nevertheless\ndisplays evidence of Sensibility--feelings and combinations of\nmovements--we must then conclude that the property specialized in\na particular tissue of the highly differentiated organism is here\ndiffused throughout.\n\nIt is obvious that the sensations or feelings of these supposed\norganisms will have a common character with the feelings of more highly\ndifferentiated organisms, although the modes of manifestation are so\nvarious. If we recognize a common character in muscular movements so\nvarious as the rhythmic pulsation of the heart, the larger rhythm of\ninspiration and expiration, the restless movements of the eye and\ntongue, the complexities of manipulation, the consensus of movements in\nflying, swimming, walking, speaking, singing, etc., so may we recognize\na common character in all the varieties of sensation. The special\ncharacter of a movement depends on the moving organ. The special\ncharacter of a sensation depends on the sensory organ. Contractility\nis the abstract term which expresses all possible varieties of\ncontraction. Sensibility--or Sentience--is the abstract term which\nexpresses all possible varieties of sensation.\n\n86. The view here propounded may find a more ready acceptance when its\napplication to all physiological questions has been tested, and it is\nseen to give coherence to many scattered and hitherto irreconcilable\nfacts. Meanwhile let a glance be taken at the inconsistencies of the\ncurrent doctrine. That doctrine declares one half of the gray substance\nof the spinal cord to be capable only of _receiving_ a sensitive\nstimulation, the other half capable only of _originating_ a motor\nstimulation. We might with equal propriety declare that one half of a\nmuscle is capable only of receiving a contractile stimulation, and the\nother half of contracting. The ingoing nerve, passing from the surface\nto the posterior part of the spinal cord, excites the activity of the\ngray substance into which it penetrates; with the anterior part of\nthis gray substance an outgoing nerve is connected, and through it\nthe excitation is propagated to a muscle: contraction results. Such\nare the facts. In our analysis we separate the sensory from the motor\naspect, and we then imagine that this ideal distinction represents a\nreal separation. We suppose a phenomenon of Sensibility independent of\na phenomenon of Contractility--suppose the one to be \u201ctransformed\u201d into\nthe other--and we then marvel \u201chow during this passage the excitation\nchanges its nature.\u201d[113]\n\n87. Before exerting ingenuity in explaining a fact, it is always well\nto make sure that the fact itself is correctly stated. _Does_ the\nneural excitation change its nature in passing from the posterior to\nthe anterior gray substance? I can see no evidence of it. Indeed the\nstatement seems to confound a neural process with a muscular process.\nThe neural process is one continuous excitation along the whole line\nof ingoing nerve, centre, and outgoing nerve, which nowhere ceases\nor changes into another process, until the excitation of the muscle\nintroduces a new factor. So long as the excitation keeps within the\nnerve-tissue, it is one and the same process of change; its issue\nin a contraction, a secretion, or a change in the conditions of\nconsciousness, depends on the organs it stimulates.\n\n88. I have already called attention to the artificial nature of all our\ndistinctions, and the necessity of such artifices. They are products of\nthat\n\n                              \u201cSecondary power\n    By which we multiply distinctions, then\n    Deem that our puny boundaries are things\n    That we perceive, and not that we have made.\u201d[114]\n\nThe distinction of Central and Peripheral systems is not simply\nanatomical, it has a physiological justification in this, that the\nCentral System is the organ of connection. Any one part of it directly\nexcited by an ingoing nerve propagates that excitation throughout\nthe whole central mass, and thus affects every part of the organism.\nTherefore we place Sensibility in it.\n\nBut this general Property subserves various Functions, according as the\nCentral System is variously related to different organs. This fact has\ngiven rise to the idea that different portions of the cerebro-spinal\naxis have different properties--which is a serious error. What is\ncertain is that the Cerebrum must have a different function from that\nof the Thalami, and the Cerebellum one different from the Medulla\nOblongata; while that of the Medulla Spinalis is different from all.\nPrecisely on the same grounds that a muscle-nerve has a different\noffice from a skin-nerve, or the pneumogastric from the acoustic.\nBut all nerves have one Neurility in common; all centres have one\nSensibility in common.\n\n\n\n\nCHAPTER V.\n\nACTION WITHOUT NERVE-CENTRES.\n\n\n89. It has long been one of the unquestioned postulates of Physiology\nthat no nerve-action can take place without the intervention of a\ncentre; and as a corollary, that all movement has its impulse--reflex\nor volitional--from a centre.[115] The postulate rests on the\nassumption that nerves derive their \u201cforce\u201d from their centre. This\nassumption we have seen to be erroneous. Yet, in consequence of its\nacceptance, experimenters have failed to notice the many examples of\nnerve-action independent of centres. Indeed, except Schiff, Goltz, and\nEngelmann, I can name no one who has ventured to suggest that movements\nmay be excited through nerves without the co-operation of centres;[116]\nnor have even they explicitly formulated the conclusion to which their\nobservations point.\n\nIt is true that the majority of muscular movements are determined by a\nreflex from centres; and that any break in the triple process of the\ningoing nerve, centre, and outgoing nerve, prevents such movements.\nIt is true that the more conspicuous and harmoniously co-ordinated\nphenomena belong to this class. But it is also demonstrable that many\nnerve-actions _may_, and some _do_, take place by direct stimulation\nof the nerve, or direct stimulation of the muscle, without the\nintervention of a centre, without even the intervention of a ganglion.\nThis must obviously be the case in animals which have no centres; and\neven in some which have well-developed nervous centres, there is every\nreason to believe that these centres often act rather in the way of\nco-ordinating than of directly stimulating actions.\n\n90. I was first led to doubt the reigning doctrine by a surprising\nobservation (frequently repeated) after I had removed the whole nervous\ncentres from a garden snail (_Helix pomatia_). The muscular mass called\n\u201cthe foot\u201d was thrown into slow but energetic contraction whenever the\nskin was pricked with the point of a scalpel, or touched with acid;\nnay, even when a glass rod dipped in the acid was brought close to,\nwithout absolutely touching, the skin, the foot curled up, and then\nslowly relaxed. The same effect was produced on the \u201cmantle\u201d--where\nthere was of course no centre. But direct irritation of the muscles\nunder the skin produced no such contraction; only through the skin\ncould the stimulation take effect. In one case I observed this strange\nphenomenon five hours after removal of the centres. It was a great\npuzzle. At first I concluded that there must be minute ganglia in\nthe skin, serving as reflex-centres. I searched for them in vain;\nand although a longer search on better methods might _possibly_ have\ndetected ganglionic cells, I soon relinquished the search, because I\nhad other grounds for believing that even the presence of abundant\nganglia would not suffice, until some better proof were afforded that\nsuch ganglia were reflex-centres.\n\n91. That direct stimulation of the nerve suffices to move the muscles,\nis familiar to all experimenters. There is no centre, or ganglion,\nin the amputated leg of the frog, which nevertheless contracts\nwhenever the sciatic nerve is stimulated. And after the nerve has been\nexhausted, and refuses to respond to any stimulus, the muscle itself\nmay be directly stimulated. Inasmuch as the movement depends on the\ncontractility of the muscles, a stimulation through centre, through\nmotor-nerve, or through muscle, will be followed by contraction. Let\nus take a clear case of reflex action. The pupil of the eye contracts\nwhen a beam of light falls on it, and dilates when the beam is shut\noff. The path of the neural process is normally this: the light\nstimulates the optic nerve, which in turn stimulates the corpora\nquadrigemina; (here the nerves which move the eye are experimentally\nproved to be stimulated;) and it is through these that the pupil is\ncaused to contract. If the optic nerve be divided, no such reflex takes\nplace--proving that the contraction does not, at least normally, come\nfrom the ciliary ganglion.\n\nBut now it is matter of observation that the pupil will contract and\ndilate under the stimuli of light and darkness, when there is no such\nreflex pathway open. Removal of the eye from the body obliterates\nthis path, cuts the eye off from all connection with the centre.\nBrown S\u00e9quard removed both eyes from a frog, placed one in a dark\nbox, and left the other exposed to the light: the pupil of the former\nwas found dilated, that of the latter contracted. On reversing the\nexperiment, and placing the eye with contracted pupil in the dark\nbox, he found it there dilate, while the dilated pupil exposed to\nthe light contracted.[117] In frogs with very irritable tissues, I\nhave found not only the pupil contracting, after the whole cranial\ncavity has been emptied, but even the eyelid close, on irritating\nthe conjunctiva[118]--yet this is one of the typical reflex actions!\nI am disposed to think that even the action of swallowing may be\nfaintly excited by stimulation of the pharynx of a brainless frog; but\nI have not observations sufficiently precise to enable me to speak\nconfidently. Goltz has, however, shown that after removal of brain\nand spinal cord and heart, there is spontaneous and active movement\nin \u0153sophagus and stomach.[119] This will no doubt be referred to the\nagency of the ganglionic plexus; but similar movements have been\nobserved by Engelmann in the ureter, and in isolated fragments of the\nureter in which not a ganglionic cell was present.[120]\n\n92. That nerves are stimulated by internal changes has long been\nrecognized with reference to \u201csubjective sensations.\u201d The divided\nnerve, in that portion which remains connected with the centre, will\nat times cause great pain. Obscure organic conditions, changes of\ntemperature, states of the blood, excite the nerves, and the patient\nfeels as if the surface of the amputated limb were irritated. It is\nall very well to call these \u201csubjective sensations\u201d; that does not\nalter the fact of the nerve being called into activity by other than\nthe normal stimuli from the surface; in like manner muscular movements\n(which are not to be explained as \u201csubjective movements\u201d) will be\nexcited by organic stimuli when motor-nerves are separated from their\ncentres. In each case it has sufficed that the nerve should be excited;\nand when excited, no matter by what means, the effect is always similar.\n\n93. Here are a few facts. Stimulation of the nerves which send\nfilaments to the chromatophores of the skin in reptiles causes the skin\nto become paler, and even colorless: the color-specks disappear under\nthis contractile stimulus. This being known, Goltz deprived a frog of\nbrain, spinal cord, and heart, thus eliminating all possible influence\nfrom them, slit up the skin of the back, and displayed the nerves which\npass from each side of the spine to the skin; these nerves he then\ndivided on the right side, and observed the skin on this side slowly\nbecome paler and paler, till finally it was as yellow as wax; the left\nside, having its nerves intact, retained its color. Two conclusions\nseemed to him warranted by this experiment: First, that even in the\ndead frog the nerves separated from their centre were still active;\nsecondly, that the irritation of the nerves resulting from their\nsection was the cause of the color-specks disappearing. This second\nconclusion was strengthened when he found that the irritation was\nincreased when he cut the nerves bit by bit.\n\nIt is not at present, I believe, clearly made out that the color-specks\nof the Cephalopoda are in direct connection with nerves; but it is\ntolerably certain that they are in some way under the influence of\nnervous stimulation, directly or indirectly. D\u2019Orbigny, indeed, goes\nso far as to say they are dependent on the will of the animal.[121]\nThis seems very lax language; but restricting ourselves to the fact\nof nervous influence, the experiments of Goltz receive further\nillustration in an observation I have elsewhere recorded.[122] I found\nthat a strip of skin taken from the dead body of a calamary (_Loligo_)\nshowed the color-specks expanding and contracting with vigor.\n\n94. The heart is well known to beat after death, if death be not the\nresult of a gradual decay. Sometimes, indeed, its muscular irritability\nis so active that the heart will beat for hours. E. Rousseau\nobserved it beating in a woman twenty-seven hours after she had been\nguillotined.[123] Not only will it beat after death, but in many\nanimals even after removal from the body: the heart of a young puppy,\nor kitten, will beat for three or four hours after its removal; that\nof a full-grown dog, or cat, not one hour; whereas the beating of that\nof a tortoise, or a frog, will, under proper precautions, be preserved\nfor days--and even after it has stopped, it may be stimulated to fresh\npulsations.\n\nPhysiologists explain this spontaneous movement of the heart as due to\nthe ganglia in its substance. This explanation, which is founded on\nwhat I cannot but regard as a purely imaginary view of the functions\nof ganglionic cells, must stand or fall with that hypothesis. A long\nand arduous investigation has led me to doubt whether in _any_ case\nthe heart\u2019s movements are primarily due to its ganglia; at all events,\nthe same spontaneous movements are observed in the hearts of molluscs\nand crustaceans, which are without even a trace of ganglia; and in the\nhearts of mammalian embryos long before ganglia or nerve-fibres make\ntheir appearance. Not less certain is it that movements of contraction\nand dilatation are produced in the blood-vessels independently of all\ncentral influence. This has been decisively proved by the Italian\nphysiologist, Mosso, when experimenting on an organ isolated from the\norganism; and although the vessels have their nerve cells and fibres,\nhe justly doubts whether it is to these that the stimulation is due,\nbecause the phenomena are observed after the nervous vitality has\ndisappeared. Goltz severed all the tissues in the leg of a rabbit,\nso that the only connection of the leg with the rest of the body was\nthrough the crural vein and artery, which kept up the circulation; yet\nalthough the nerves of the skin were thus separated from their centre,\nso that no sensation could be produced by stimulating the skin of the\nleg, consequently no reflex from the centre on the vessels, Goltz found\nthat a marked reddening of the skin from congestion of the capillaries\nfollowed the application of mustard to the skin. Physiologists who\nbelieve that the constriction and dilatation of blood-vessels are due\nto the action of the ganglionic cells distributed over the walls of the\nvessels will explain Goltz\u2019s observation as a case of reflex action;\nbut those who agree with me that such an hypothesis respecting the part\nplayed by the cells is untenable, will class the observation among\nother cases of direct stimulation.\n\n95. But passing from these perhaps questionable cases, let us glance\nat other cases. The mobile iris of the bird displays movements after\nthe nerves have been divided. Even the voluntary striped muscles are\nnot altogether motionless. Schiff divided the hypoglossus on one side,\nand found, of course, the tongue paralyzed on that side; but he also\nfound that on the third day after the operation some of the muscles of\nthat side were quivering: the agitation spread to others, till by the\nend of the fourth day all the fibres were _rhythmically_ contracting.\nFrom this time onwards, the contractions were incessant; though they\nwere never able to move the tongue, because the fibres did not contract\nsimultaneously.\n\nSchiff also observed that the hairs over the eyes and the \u201cwhiskers\u201d of\ncats, rabbits, and guinea pigs were for months after section of their\nnerves in incessant rhythmical vibration. This was observed when the\nanimals were asleep as when awake. Valentin records the spontaneous\nmovements in the diaphragm of animals just killed; and this even after\nsection of the phrenic nerve. The same movements may be seen in the\noperculum of fishes. Henle observed the spontaneous contractions of the\nintercostal muscles; which Schiff confirms, adding that the movements\nobserved by him in cats and birds were not simply contractions of some\nfibres, but of all the muscles, so that three or four excised ribs\nrhythmically contracted and expanded.\n\nI have performed a great many experiments with a view of determining\nthis question, but the phenomena were so variable that I refrain\nfrom adducing any,[124] and merely state the general result as one\nin harmony with the foregoing examples. The great variability of the\nphenomena depends upon the variable conditions of muscular irritability\nand anatomical relations. When the heart of one woman is found beating\ntwenty-seven hours after death, while in most men and women it ceases\nafter a few minutes, we must be prepared to find different, and even\ncontradictory phenomena under varying unknown conditions. There\nis, however, a general agreement among experimenters that muscular\nirritability increases after separation from nerve-centres, and then\nquickly decreases again.\n\n96. Although the stimulation of muscles usually comes _through_ a\nnerve-centre, yet since the muscles do not derive their Contractility\nfrom nerve-centres any stimulation will suffice. Now since we have\nabundant proof that sensory nerves are stimulated by certain organic\nchanges, by poisons in the blood, excess of carbonic acid, etc., we\nare justified in concluding that motor nerves will be stimulated in\nlike manner, and thus muscular movement be produced occasionally\nwithout the intervention of a centre. Pressure on a motor nerve, or the\nirritation which results from inflammation, will determine contraction,\nor secretion directly. Recently, Erb and Westphal have disclosed\nthe fact that the leg will be suddenly jerked out if the patella be\ngently tapped; and they prove this not to be a reflex action, because\nit follows with the same certainty after the skin has been made\ninsensible.[125]\n\nThere are doubtless many other phenomena which, though commonly\nassigned to reflex stimulation, are really due to direct stimulation.\nResearch might profitably be turned towards the elucidation of this\npoint. Since there is demonstrable evidence that a nerve when no\nlonger in connection with its centre, or with ganglionic cells, may\nbe excited by electricity, pressure, thermal and chemical stimuli, we\nmust conclude that even when it is in connection with its centre, any\nlocal irritation from pressure, changes in the circulation, etc., will\nalso excite it. But as such local excitations will have only local and\nisolated effects, they will rarely be conspicuous.\n\n\n\n\nCHAPTER VI.\n\nWHAT IS TAUGHT BY EMBRYOLOGY?\n\n\n97. Subject to the qualification expressed in the last chapter,\nstimulation of muscles and glands involves a neural process in ingoing\nnerve, centre, and outgoing nerve. These are the triple elements of the\n\u201cnervous arc.\u201d If muscles were directly exposed to external influences,\nthey would be stimulated without the intervention of a centre; but as a\nmatter of fact they never are thus exposed, being always protected by\nthe skin. Did the skin-nerves pass directly to the muscles underneath,\nthey would move those muscles, without the intervention of a centre;\nbut as a matter of fact the skin-nerves pass directly to a centre, so\nthat it is only _through_ a centre that they can act upon the muscles.\nWere muscles and glands directly connected with sensitive surfaces,\ntheir activity would indeed be awakened by direct stimulation; but\nunless the muscles were so connected the one with the other, by\nanastomosis of fibres or continuity of tissue, that the movement of\none was the movement of all, there would need to be some other channel\nby which their separate energies should be combined and co-ordinated.\nIn the higher organisms anastomosis of muscles is rare, and the\ncombination is effected by means of the nerves.\n\n98. Although analysis distinguishes the two elements of the\nneuro-muscular system, assigning separate properties to the separate\ntissues, an interpretation of the phenomena demands a synthesis, so\nthat a movement is to be conceived as always involving Sensibility,\nand a sensation as always involving Motility.[126] In like manner,\nalthough analysis distinguishes the various organs of the body,\nassigning separate functions to each, our interpretation demands their\nsynthesis into an organism; and we have thus to explain how the _whole_\nhas different _parts_, and how these different parts are brought into\nunity. Embryology helps us to complete the fragmentary indications of\nAnatomy and Physiology.\n\n99. Take a newly laid egg, weigh it carefully, then hatch it, and when\nthe chick emerges, weigh both chick and shell: you will find that\nthere has been no increase of weight. The semifluid contents have\nbecome transformed into bones, muscles, nerves, tendons, feathers,\nbeak, and claws, all without increase of substance. There has been\n_differentiation_ of structure, nothing else. Oxygen has passed into\nit from without; carbonic acid has passed out of it. The molecular\nagitation of heat has been required for the rearrangements of the\nsubstance. Without oxygen there would have been no development. Without\nheat there would have been none. Had the shell been varnished, so as to\nprevent the due exchange of oxygen and carbonic acid, no chick would\nhave been evolved. Had only one part of the shell been varnished, the\nembryo would have been deformed.\n\n99_a_. The patient labors of many observers (how patient only those\ncan conceive who have made such observations!) have detected something\nof this wondrous history, and enabled the mind to picture some of the\nincessant separations and reunions, chemical and morphological. Each\nstage of evolution presents itself as the consequence of a preceding\nstage, at once an emergence and a continuance; so that no transposition\nof stages is possible; each has its appointed place in the series\n(PROBLEM I. \u00a7 107). For in truth each stage is a _process_--the sum of\na variety of co-operant conditions. We, looking forward, can foresee in\neach what it will become, as we foresee the man in the lineaments of\nthe infant; but in this prevision we always presuppose that the regular\ncourse of development will proceed unchecked through the regular\nsuccession of special conditions: the infant becomes a man only when\nthis succession is uninterrupted. Obvious as this seems, it is often\ndisregarded; and the old metaphysical conception of _potential_ powers\nobscures the real significance of Epigenesis. The potentiality of the\ncells of the germinal membrane is simply their capability of reaching\nsuccessive stages of development under a definite series of co-operant\nconditions. We foresee the result, and personify our prevision. But\nthat result will not take place unless all the precise changes that\nare needful serially precede it. A slight pressure in one direction,\ninsufficient to alter the chemical composition of the tissue, may so\nalter its structure as to disturb the regular succession of forms\nnecessary to the perfect evolution.\n\n100. The egg is at first a microscopic cell, the nucleus of which\ndivides and subdivides as it grows. The egg becomes a hollow sphere,\nthe boundary wall of which is a single layer of cells, all so\nsimilar that to any means of appreciation we now possess they are\nindistinguishable. They are all the progeny of the original nucleus\nand yolk, or cell contents. Very soon, however, they begin to show\ndistinguishable differences, not perhaps in _kind_, but in _degree_.\nThe wall of this hollow sphere is rapidly converted into the _germinal\nmembrane_, out of which the embryo is formed. Kowalewsky (confirmed by\nBalfour) has pointed out how in the Amphioxus the hollow sphere first\nassumes an oval shape, and then, by an indentation of the under side,\nwith corresponding curvature of the upper side, presents somewhat\nthe shape of a bowl. The curvature increases, and the curved ends\napproaching each other, the original cavity is reduced to a thin line\nseparating the upper from the under surface. The cavity of the body is\nformed by the curving downwards of this double layer of the germinal\nmembrane.\n\n101. This is not precisely the course observable in other vertebrates;\nbut in all, the germinal membrane, which lies like a watch-glass on the\nsurface of the yolk, is recognizable as two distinct layers of very\nsimilar cells. What do these represent? They are the starting-points\nof the two great systems: Instrumental and Alimental. The one yields\nthe dermal surface; the other the mucous membrane. Each follows an\nindependent though analogous career. The yolk furnishes nutrient\nmaterial to the germinal membrane, and so passes more or less directly\ninto the tissues; but unlike the germinal membrane, it is not itself\nto any great extent the seat of generation by segmentation. There are\ntwo yolks: the yellow and the white (which must not be confounded\nwith what is called the _white of egg_); and their disposition may be\nseen in the diagram (Fig.\u00a014) copied from Foster and Balfour\u2019s work.\nThe importance of the white yolk is that it passes insensibly into\na distinct layer of the germinal membrane, between the two primary\nlayers.[127] Each of the three layers of the germinal membrane has its\nspecific character assigned to it by embryologists, who, however, are\nnot all in agreement. Some authorities regard the topmost layer as\nthe origin of the nervous system, the epidermis, with hair, feathers,\nnails, horns, the cornea and lens of the eye, etc. To the middle layer\nare assigned the muscular and osseous systems, the sexual organs, etc.\nTo the innermost layer, the alimentary canal, with liver, pancreas,\ngastric and enteric glands. Other authorities are in favor of two\nprimary layers: one for the nervous, muscular, osseous, and dermal\nsystems; the other for the viscera and unstriped muscles. Between these\ntwo layers, a third gradually forms, which is specially characterized\nas the vascular.\n\n[Illustration:\n\n    Fig.\u00a014.--_Diagrammatic section of an unincubated hen\u2019s egg._ _bl_,\n    blastoderm; _w\u00a0y_, white yolk; _y\u00a0y_, yellow yolk; _v\u00a0t_, vitelline\n    membrane; _x_ and _w_, layers of albumen; _ch l_, chalaza; _a ch_,\n    air-chamber; _i\u00a0s\u00a0m_, internal layer of shell membrane; _s\u00a0m_,\n    external layer; _s_, shell.\n]\n\n102. Messrs. Foster and Balfour, avoiding the controverted designations\nof serous, vascular, and mucous layers, or of sensorial, motor\ngerminative, and glandular layers, employ designations which are\nindependent of theoretic interpretation, and simply describe the\nposition of the layers, namely, _epiblast_ for the upper, _mesoblast_\nfor the middle, and _hypoblast_ for the under layer. From the epiblast\nthey derive the epidermis and central nervous system (or would even\nlimit the latter to the central gray matter), together with some\nparts of the sense-organs. From the mesoblast, the muscles, nerves\n(and probably white matter of the centres), bones, connective tissue,\nand blood-vessels. From the hypoblast, the epithelial lining of the\nalimentary canal, trachea, bronchial tubes, as well as the liver,\npancreas, etc.[128] K\u00f6lliker\u2019s suggestion is much to the same effect,\nnamely, that the three layers may be viewed as two epithelial layers,\nbetween which subsequently arises a third, the origin of nerves,\nmuscles, bones, connective tissue, and vessels.[129]\n\n103. The way in which the history may be epitomized is briefly this:\nThere are two germinal membranes, respectively representing the\nInstrumental and Alimental Systems. Each membrane differentiates, by\ndifferent appropriations of the yolk substance, into three primary\nlayers, _epithelial_, _neural_, and _muscular_. In the epiblast, or\nupper membrane, these layers represent: 1\u00b0, the future epidermis\nwith its derivatives--hair, feathers, nails, skin glands, and\nchromatophores; 2\u00b0, the future nervous tissue; 3\u00b0, the future muscular\ntissue.[130] (Bone, dermis, connective tissue, and blood-corpuscles are\nsubsequent formations.)\n\nThe hypoblast, or under membrane, in an inverted order presents a\nsimilar arrangement: 1\u00b0, the unstriped muscular tissue of viscera and\nvessels; 2\u00b0, the nervous tissue of the sympathetic system; 3\u00b0, the\nepithelial lining of the alimentary canal with its glands.\n\nFundamentally alike as these two membranes are, they have specific\ndifferences; but in both we may represent to ourselves the\n_embryological unit_ constituted by an epithelial cell, a nerve-cell,\nand a muscle-cell. All the other cells and tissues are adjuncts,\nnecessary, indeed, to the working of the vital mechanism, but\nsubordinated to the higher organites.\n\n104. This conception may be compared with that of His in the\ndivision of Archiblast and Parablast assigned by him to the germ\nand accessory germ.[131] We can imagine, he says, the whole of the\nconnective substances removed from the organism, and thus leave behind\na scaffolding in which brain and spinal cord would be the axis,\nsurrounded by muscles, glands, and epithelium, and nerves as connecting\nthreads. All these parts stand in more or less direct relation to the\nnervous system. All are continuous. By a similar abstraction we can\nimagine this organic system removed, and leave behind the connected\nscaffolding which is formed from the accessory germ; but this latter\nhas only _mechanical_ significance; the truly vital functions belong to\nthe other system.\n\n105. The researches of modern histologists have all converged towards\nthe conclusion that the organs of Sense are modifications of the\nsurface, with epithelial cells which on the one side are connected with\nterminal hairs, or other elements adapted to the reception of stimuli,\nand are connected on the other side through nerve-fibres with the\nperceptive centres. It has been shown that nerve-fibres often terminate\nin (or among) epithelial cells--sensory fibres at the surface, and\nmotor-fibres in the glands.[132] Whether the fibres actually penetrate\nthe substance of the cell, or not, is still disputed. Enough for\nour present purpose to understand that there is a _physiological_\nconnection between the two, and above all that sensory nerves are\nnormally stimulated through some epithelial structure or other.\n\n[Illustration:\n\n    Fig.\u00a015.--_Transverse section of a Blastoderm incubated for\n    eighteen hours._ The section passes through the medullary groove,\n    _m\u00a0e_. A, epiblast. B, mesoblast. C, hypoblast. _m\u00a0f_, medullary\n    fold, _c\u00a0h_, notochord.\n]\n\n106. And this becomes clear when we go back to the earliest indications\nof development. Look at Fig.\u00a015, representing a transverse section of\nthe germinal membranes in a chick after eighteen hours\u2019 incubation.\nHere the three layers, A, B, and C, have the aspect of simple cells\nvery slightly differing among each other. Yet since each layer has\nultimately a progeny which is characteristically distinguishable, we\nmay speak of each not as what it now is, but what it will become.\nAlthough the most expert embryologist is often unable to distinguish\nthe embryo of a reptile from that of a bird or of a mammal, at certain\nstages of evolution, so closely does the one resemble the other, yet\ninasmuch as the embryo of a reptile does not, cannot become a bird, nor\nthat of a bird a mammal, he is justified in looking forward to what\neach will become, and in calling each embryo by its future name. On the\nsame ground, although we cannot point to any such distinction between\nthe layers of the blastoderm as I have indicated in the separation\nof Instrumental and Alimental Systems, nor specify any characters by\nwhich the cells can be recognized as epithelial, neural, and muscular,\nyet a forward glance prefigures these divisions. We know that the\nfirst result of the segmentation of the yolk is the formation of cells\nall alike, which in turn grow and subdivide into other cells. We\nknow that these cells become variously modified both in composition\nand structure, and that by such differentiations the simple organism\nbecomes a complex of organs.\n\n107. But here it is needful to recall a consideration sometimes\ndisregarded, especially by those who speak of Differentiation as if\nit were some magical Formative Principle, quite independent of the\nstate of the organized substance which is formed. There is a luminous\nconception--first announced by Goethe, and subsequently developed by\nMilne Edwards--which regards the organism as increasing in power and\ncomplexity by a physiological \u201cdivision of labor,\u201d very similar to\nthat division of employments which characterizes the developed social\norganism. But the metaphor has sometimes been misleading; it has been\ninterpreted as indicating that Function creates Organ (see PROBLEM I.\n\u00a7 88), and as if Differentiation itself were something more than the\nexpression of the changes resulting from the introduction of different\nelements. In the Social Organism a \u201cdivision of labor\u201d presupposes\nthat laborers with their labor-materials are already existing; the\nchange is one of rearrangement: instead of each laborer employing\nhis skill in doing many kinds of work, he restricts it to one kind,\nwhich he is then able to do with less loss of time and power. Thus is\nsocial power multiplied without increase of population, and the social\norganism becomes more complex by the differentiation of its organs. It\nis not precisely thus with the Animal Organism during its evolution.\nIndeed to suppose that the differentiation of the germinal membrane\ninto special tissues and organs takes place by any such division\nof employments, is to fall into the ancient error of assuming the\norganism to exist _preformed_ in the ovum. The unequivocal teaching of\nEpigenesis is that each part is produced out of the elements furnished\nby previous parts; and for every differentiation there must be a\ndifference in composition, structure, or texture--the first condition\nbeing more important than the second, the second more important than\nthe third. The word protoplasm has almost as wide a generality as\nthe word animal, and is often used in forgetfulness of its specific\nvalues: the protoplasm of a nerve-cell is not the _same_ as that of\na blood-cell, a muscle-cell, or a connective-tissue cell, any more\nthan a bee is a butterfly, or a prawn a lobster. No sooner has the\nspecific character been acquired, no sooner is one organite formed\nby differentiation, than there is an absolute barrier against any\ntransformation of it into any other kind of organite. The nerve-cell,\nmuscle-cell, and epithelial cell have a common starting-point, and a\ncommunity of substance; but the one can no more be transformed into\nthe other than a mollusc can be transformed into a crustacean. In the\nhomogeneous cellular mass which subsequently becomes the \u201cvertebral\nplates,\u201d a group of cells is very early differentiated: this is the\nrudimentary spinal ganglion, which becomes enveloped in a membrane,\nand then pursues a widely different course from that of the other\ncells surrounding it, so that \u201cthe same cell which was formerly an\nelement of the vertebral plate now becomes a nerve-cell, while its\nneighbors become cartilage-cells.\u201d[133] Indeed all the hypotheses\nof transformation of tissues by means of Differentiation are as\nunscientific as the hypotheses of the transformation of animals. In the\norganism, as in the Cosmos, typical forms once attained are retained.\nThere probably was a time in the history of the animal series when\nmasses of protoplasm by appropriating different materials from the\nsurrounding medium were differentiated into organisms more complex and\nmore powerful than any which existed before. But it is obvious that\nfrom a common starting-point there could have been no variations in\ndevelopment without the introduction of new elements of composition:\nthere might have been many modifications of structure, but unless\nthese facilitated modifications of composition, there could never have\nresulted the striking differences observed in animal organisms.[134]\n\n108. To return from this digression, we may liken the three primary\nlayers of the germinal membranes to the scattered and slightly\ndifferent masses of protoplasm out of which the animal kingdom\nwas developed. In this early stage there are no individualized\norganites--no nerve-cells or muscle-cells. They are cells ready to\nreceive modifications both of composition and structure, appropriating\nslightly different elements from the yolk, and according to such\nappropriation acquiring different properties. And this is necessarily\nso, since the different cells have not exactly the same relation to\nthe yolk, nor are they in exactly the same relation to the incident\nforces which determine the molecular changes. The uppermost layer\n(epiblast) under such variations develops into epithelium and central\nnerve-tissue; the epithelial cell cannot develop into a nerve-cell, the\ntwo organites are markedly unlike, yet both spring from a common root.\nAnother modification results in the development of muscle-cells from\nthe inner layer.\n\n109. Hence we can understand how the surface is sensitive even\nin organisms that are without nerve-tissue; and also how even in\nthe highest organisms there is an intimate blending of epithelial\nwith neural tissues. The same indication explains the existence\nof neuro-muscular cells in the _Hydra_, recorded by Kleinenberg,\nand of neuro-muscular fibres in the _Bero\u00eb_, by Eimer.[135] In the\nsimpler organisms the surface is at once protective, sensitive, and\nabsorbent. It shuts off the animal from the external medium, and thus\nindividualizes it; at the same time it connects this individual with\nthe medium; for it is the channel through which the medium acts, both\nas food and stimulus. The first morphological change is one whereby\na part of the surface is bent inwards, and forms the lining of the\nbody\u2019s cavity. Soon there follows such a modification of structure\nbetween the outer and inner surfaces (_ectoderm_ and _endoderm_) that\nthe one is mainly sensitive and protective, the other mainly protective\nand absorbent. The outer surface continues indeed to absorb, but its\npart in this function is insignificant compared with that of the inner\nsurface, which not only absorbs but secretes fluids essential to\nassimilation. The inner surface, although sensitive, is subjected to\nless various stimulation, and its sensibility is more uniform.\n\n110. The uppermost of the primary layers we have seen to be epithelial;\nand we know that the first lines of the central nervous system are laid\nthere. A depression called the medullary groove is the first indication\nof the future cerebro-spinal axis. Some writers--K\u00f6lliker, for\ninstance--regard this medullary groove as continuous with but different\nfrom the epithelial layer; others maintain that it lies underneath the\nepithelium, just as we see it in later stages, when the differentiation\nbetween epithelial and nerve cell has taken place. Since no one\ndisputes the fact that when the groove becomes a closed canal its\nlining is epithelial, one of two conclusions is inevitable: either\nthe cells of the primary layer develop in the two diverse directions,\nepithelial and neural; or else epithelial cells can be developed on\nthe surface of neural cells and out of them. The latter conclusion is\none which, involving the conception of transformation, would seem to\nbe put out of court. I think, then, we must admit that the under side\nof the primary layer of cells becomes differentiated into nerve-cells;\nand this is in accordance with the observations of Messrs. Foster and\nBalfour.[136]\n\n111. While there is this intimate morphological and physiological\nblending of epithelial and neural organites, there is an analogous\nrelation between neural and muscular organites. As the neural layer\nlies under the epithelial, the muscular lies under the neural. The\nsurface stimulation passes to the centre, and is reflected on the\nmuscles. Embryology thus teaches why a stimulus from the external\nmedium must be propagated to a nerve-centre before it reaches the\nmuscles; and why a stimulus on one part of the surface may set all the\norganism in movement, by passing through a centre which co-ordinates\nall movements. This, of course, only applies to the higher organisms.\nIn the simpler structures the sensitive surface is directly continuous\nwith the motor organs.\n\nIt is unnecessary here to pursue this interesting branch of our\nsubject; nor need we follow the analogous evolution of the second\ngerminal membrane representing the Alimental System. Our attention\nmust be given to what is known and inferred respecting the elementary\nstructure of the nerves and centres, on which mainly the interest of\nthe psychologist settles, since to him the whole of Physiology is\nmerged in nerve actions.\n\n\n\n\nCHAPTER VII.\n\nTHE ELEMENTARY STRUCTURE OF THE NERVOUS SYSTEM.\n\n\n112. The progress of science involves an ever-increasing Analysis.\nInvestigation is more and more directed towards the separated details\nof the phenomena previously studied as events; the observed facts\nare resolved into their component factors, complex wholes into their\nsimpler elements, the organism into organs and tissues. But while the\nanalytical process is thus indispensable, it is, as I have often to\ninsist, beset with an attendant danger, namely, that in drawing the\nattention away from one group of factors to fix it exclusively on\nanother, there is a tendency to forget this artifice, and instead of\nrestoring the factors provisionally left out of account, we attempt a\nreconstruction in oblivion of these omitted factors. Hence, instead\nof studying the properties of a tissue in all the elements of that\ntissue, and the functions of an organ in the anatomical connections\nof that organ, a single element of the tissue is made to replace the\nwhole, and very soon the function of the organ is assigned to this\nparticular element. The \u201csuperstition of the nerve-cell\u201d is a striking\nillustration. The cell has usurped the place of the tissue, and has\ncome to be credited with central functions; so that wherever anatomists\nhave detected ganglionic cells, physiologists have not hesitated\nto place central functions. By such interpretations the heart and\nintestines, the glands and blood-vessels, have, erroneously, I think,\ntheir actions assigned to ganglionic cells.\n\nIt is unnecessary to point out the radical misconception which thus\nvitiates a great mass of anatomical exposition and physiological\nspeculation. I only call the reader\u2019s attention to the point at the\noutset of the brief survey we have now to make of what is known\nrespecting the elementary structure of the nervous system.\n\n\nDIFFICULTIES OF THE INVESTIGATION.\n\n113. So great and manifold are the difficulties of the search, that\nalthough hundreds of patient observers have during the last forty years\nbeen incessantly occupied with the elementary structure of the nervous\nsystem, very little has been finally established. Indeed, we may still\nrepeat Lotze\u2019s sarcasm, that \u201cmicroscopic theories have an average of\nfive years\u2019 duration.\u201d This need not damp our ardor, though it ought to\ncheck a too precipitate confidence. Nothing at the present moment needs\nmore recognition by the student than that the statements confidently\nrepeated in text-books and monographs are very often for the most part\nonly ingenious guesses, in which Observation is to Imagination what\nthe bread was to the sack in Falstaff\u2019s tavern bill. Medical men and\npsychologists ought to be warned against founding theories of disease,\nor of mental processes, on such very insecure bases; and physiological\nstudents will do well to remember the large admixture of Hypothesis\nwhich every description of the nervous system now contains. Not that\nthe potent aid of Hypothesis is to be undervalued; but its limits must\nbe defined. It may be used as a finger-post, not as a foundation. It\nmay suggest a direction in which truth may be sought; it cannot take\nthe place of Observation. It may link together scattered facts; it\nmust not take the place of a fact. We are glad of corks until we have\nlearned to swim. We are glad of a suggestion which will for the nonce\nfill up the gaps left by observation, and hold the facts intelligibly\ntogether. And both as suggestion and colligation, Hypothesis is\nindispensable. Indeed, every _discovery_ is a verified hypothesis;\nand there is no discovery until verification has been gained: up\nto this point it was a guess, which might have been erroneous--a\ntorchbearer sent out to look for a missing child in one direction,\nwhile the child was wandering in another; only when he finds the\nchild can we acknowledge that the torchbearer pursued the right path.\nHypothesis satisfies the intellectual need of an explanation, but we\nmust be wary lest we accept this fulfilment of a need as equivalent\nto an enlargement of knowledge; we must not accept explanation as\ndemonstration, and suppose that because we can form a mental picture\nof the possible stages of an event, therefore this picture represents\nthe actual stages. Let us be alert, forewarned against the tendency to\nseek evidence in support of a conclusion, instead of seeking to unfold\nthe conclusion step by step from the evidence. To seek for evidence in\nsupport of a _guess_ is very different from seeking it in support of\na _conclusion_; which latter practice is like that of people asking\nadvice, and only following it when it chimes in with their desires.\n\n114. Is not the warning needed, when we find anatomists guided by\ncertain \u201cphysiological postulates,\u201d and consequently _seeing_ only\nwhat these postulates demand? For example, there is the postulate of\n\u201cisolated conduction,\u201d which is said to require that every nerve-fibre\nshould pursue its course singly from centre to periphery. Accordingly\nthe fibres are described as unbranched. Whatever may be the demand\nof the postulate, or the felt necessity of the deduction, the fact\nis that nerve-fibres do branch off during their course at various\npoints; nay, it is doubtful whether any lengthy fibre is unbranched.\nOther postulates demand what fact plainly denies. It is said to be\n\u201cnecessary\u201d that every cell should have at least two fibres, and that\nsensory and motor nerves should be directly connected through their\nrespective cells. These things cannot be seen, but they are described\nwith unhesitating precision. Diagrams are published in which the\nsensory fibres pass into the cells of the posterior horn of the spinal\ncord, and these cells send off prolongations to the cells of the\nanterior horn, and thence the motor fibres pass out to the muscles:\nan absolutely impossible arrangement, according to our present data!\nAgain, the postulate that nerve-force originates in the cells, and that\nnerve-functions depend on cells, required that the cells should be most\nabundant where the function was most energetic. Of course they were\nfound most abundant in the required places--no notice whatever being\ntaken of the facts which directly contradicted the deduction.\n\n115. Among the serious obstacles to research we must reckon this\ntendency to substitute Imaginary Anatomy for Objective Anatomy. I am\nconscious of the tendency in myself, as I note it in others; and have\nconstantly to struggle against it, though not perhaps always aware of\nit. Many a time have I had to relinquish plausible explanations, which\nwould have supported my speculations could I but have believed that\nthey represented the facts; but being unable to believe this, I had to\nremember that hypotheses and explanations appear and disappear--only\nthe solid fact lives. If there is one lesson emphatically taught by\nPhilosophy, it is the unwisdom of founding our conclusions on our\ndesires rather than on the objective facts.\n\n116. In the following pages a constantly critical attitude is\npreserved: this is simply to keep active the sense of how much is still\nneeded to be done before a satisfactory theory of the nervous system\ncan be worked out. The objective difficulties are greater than in any\nother department of Anatomy. The problem is to form a precise picture\nof what the organites are, and of how they are arranged in the living\ntissue; yet our present means of investigation involve as a preliminary\nthat we should _alter_ that arrangement, _removing_ some elements of\nthe tissue, and _changing_ the state of others, without knowing what\nwere their precise state and arrangement before the change. Place a\npiece of nerve-tissue under the microscope, without having subjected\nit to various mechanical and chemical operations, and you can see next\nto nothing of its structure. You must tear the parts asunder, and\nremove the fat and nerve-sap (plasmode) before you can see anything;\nyou must coagulate the albumen, and otherwise chemically alter the\nsubstances before a thin section can be made; you must get rid of\nthe tissues in which it is embedded, without knowing what are the\nconnections thus destroyed. Living neurine has no greater consistence\nthan cream, often no greater than oil. How, then, can thin sections\nbe made until this viscid substance has been hardened by alcohol or\nacids? But substances thus acted on lose their constituent water,\nwhich can no more be removed without alteration of their structure,\nthan it can be removed from certain salts without destruction of their\nspecial properties. Losing their water alone, they become deformed.\nThey lose much more. Sometimes the loss can be estimated, as in the\ncase of the hyaline substance investing the nucleus during the process\nof segmentation in embryonic cells, which may be seen to disappear when\na weak solution of acid is applied.[137] At other times we are unable\nto say what has disappeared. Under different modes of preparation very\ndifferent appearances are observed, and anatomists are accordingly at\nvariance. Yet unless some hardening method be adopted little can be\nseen! Stilling, who has given his life to the study, declares that no\nresults are reliable which are obtained from the unprepared tissue,\nbecause the mechanical isolation of the elements destroys the textural\narrangement.[138] There is one method of hardening, and only one, which\nwe can be certain does not chemically alter the structure, and that\nis the freezing method. The experiments of Dr. Weir Mitchell and Dr.\nRichardson prove this, because they prove that the brain of the living\nanimal may be frozen and frozen again and again, yet recover its vital\nactivity when thawed. Professor Rutherford has invented an admirable\ninstrument for making sections of the frozen tissue, of any delicacy\nthat may be required; but with the thinnest section there will still be\ncertain difficulties of observation, unless the tissue has undergone a\nstaining process. Whatever is seen, however, in the frozen tissue is to\nbe accepted as normal.\n\n117. Two points must be determined before reliance can be placed on\nobservations of tissues chemically acted on: First, we must prove that\nthe forms now visible existed before the preparation--the chemical\naction merely unveiling them; secondly, we must estimate the part\nplayed by the elements which have been removed in order to make the\nrest visible. We know, for example, that the nucleus often exists in\nthe cell, though an acid may be needed to make it visible. We also\nknow that cells which during life are quite free from visible granules\nare distinctly granulated after death, even without external chemical\naction. Imagine the explanation of a steam-engine to be attempted by\nfirst taking it to pieces, and examining these pieces, with no account\nof the coals and steam which had previously been _removed_ in order to\nfacilitate the examination. When we know the part played by coals and\nsteam, we may disregard these items of the active machine. So when we\nknow the part played by water, fat, amorphous substance, and plasmode,\nwe may describe nerve-tissue without taking these into account.\n\n118. \u201cYou have convinced me,\u201d said Rasselas to Imlac, \u201cthat it is\nimpossible to be a poet.\u201d My readers may, perhaps, infer from this\nenumeration of the difficulties that a knowledge of the minute anatomy\nof the nervous system is impossible. Not so; but a knowledge of these\ndifficulties should impress us with the necessity for a vigilant\nscepticism, and the search after new methods. If the difficulties\nare fairly faced, they may be finally overcome. What we must resign\nourselves to at present is the conviction that our knowledge is not\nsufficiently accurate to be employed as a basis of deduction in the\nexplanation of physiological and psychological processes.[139]\n\n119. Having said so much, let me add that there are some positive\nmaterials, and these yearly receive additions. The organites are\ndescribed with a general agreement as to their composition and\nstructure--although there is much that is hypothetical even here.\nNeurine is known under two aspects: the amorphous and the figured. The\nfigured, which is the better known, comprises cells of different kinds,\nfibres and fibrils. The amorphous, more generally called _Neuroglia_,\nor nerve-cement, is less understood, and is indeed by many authorities\nexcluded altogether from the nerve-tissue proper, and relegated to the\nclass of connective tissues.\n\n\nTHE NERVE-CELL.\n\n120. It is unfortunate that the term nerve-cell is applied to organites\nof very variable structure. Nerve-cell is a generic term of which\nthe species are many; under it are designated organites in different\nstages--as infancy, childhood, and manhood are all included under Man.\nMost commonly by nerve-cell is understood the ganglionic corpuscle,\nconspicuous in its size and its prolongations, such as it appears in\nthe great centres, and in ganglia. It also designates smaller different\norganites, sometimes called \u201cnuclei\u201d (_Kerne_), sometimes grains\n(_K\u00f6rner_). There would be advantage in designating the earlier stages\nas _neuroblasts_, reserving the word _cells_ for the more developed\nforms. Such a distinction would facilitate the discussion of whether\nnerve-fibres had or had not their origin in cells; because while I, for\none, see very coercive evidence against the accepted notion that all\nthe fibres have their origin in the processes of ganglionic corpuscles,\nI see no reason to doubt that both fibres and corpuscles have their\norigin in neuroblasts. Of this anon.\n\nThe cell is a composite organite, the primary element being a\nmicroscopic mass of protoplasm, or what may more conveniently be\ntermed _neuroplasm_. It appears as finely granulated and striated\nor fibrillated substance on a hyaline ground, with water, fat, and\ndiffused pigment in varying quantities. The cell contains a nucleus,\nand nucleolus--sometimes two. Like other animal cells, it sometimes has\na distinct cell-wall, sometimes not. Its size and shape are variable:\nsometimes distinctly visible to the naked eye, generally visible only\nunder the microscope.[140] It is round, oval, pyramidal, club-shaped,\npear-shaped, or many-cornered. It has one, two, three, or many\noutgrowths called \u201cprocesses,\u201d and according to the processes it is\nknown as unipolar, bipolar, and multipolar. When there are no processes\nthe cell is called apolar. Some idea of these processes may be formed\nif they are likened to the pseudopodia of Am\u0153b\u00e6 and Foraminifera.\nCompare Fig.\u00a016, a nerve-cell, figured by Gerlach, with Fig.\u00a017, one\nhighly magnified, in which Max Schultze\u2019s hypothesis is represented.\n\n[Illustration:\n\n    Fig.\u00a016.--_Nerve-cell from anterior horn of spinal cord (man),\n    magnified 150 diameters._ _a_, cell process unbranched passing into\n    or joining an axis cylinder, the other processes are branched; _b_,\n    pigment. The nucleus and nucleolus are visible.\n]\n\n[Illustration: Fig.\u00a017.--_Nerve-cell from the anterior gray substance\nof the spinal cord of a calf magnified 600._ _a_, the axis cylinder;\n_b_, the branched process. The neuroplasm is represented as distinctly\nfibrillated, with granular substance interspersed. Nucleus and\nnucleolus very distinct.]\n\n121. Such is a general description of the nerve-cell as it is seen in\nvarious places, and under various modes of preparation. How much is\ndue to preparation we cannot positively say. While we always discover\nfibrine in the blood after it is withdrawn from the vessels, we know\nthat fibrine as such does not exist in the circulating blood. And if\nneurine is a semi-liquid substance, we may doubt whether in the living\ncell it is fibrillated. Doubts have been thrown even on the normal\nexistence of the granular substance, which has been attributed to\ncoagulation. Thus we know that the nucleus of the white blood-corpuscle\nappears perfectly homogeneous until subjected to heat, yet at a certain\ntemperature (86\u00b0 F.) it assumes the aspect of a fine network. Haeckel\nobserved the hyaline substance of the neurine in crayfish become\ntroubled and changed directly any fluid except its own blood-serum\ncame in contact with it. Leydig noticed the transparent ganglion of a\nliving Daphnia become darker and darker as the animal died; and I saw\nsomething like this, after prolonged struggles of a Daphnia to escape\nfrom a thread in which its leg was entangled. Charles Robin, indeed,\nasserts that the passage from the hyaline to the finely granulated\nstate is a characteristic of the dying cell.[141] On the other hand,\nit should be noted that Max Schultze describes a fibrillated appearance\nin cells just removed from the living animal, and placed in serum.\n\nWhen, therefore, one observer describes the neuroplasm as being clear\nas water, another as finely granular, and a third as fibrillated,\nwe must conclude that the observations refer to cells, 1\u00b0, under\ndifferent states of vitalization, or, 2\u00b0, under different modes of\npreparation. On the first head we note that some nerve-cells are so\nperishable that Trinchese declares he could find no cells in the\nganglia of a cuttlefish which had been dead twenty-four hours, although\nthey were abundant in one recently killed.[142] On the second head\nwe note that the changes wrought by modes of preparation cannot be\nleft out of consideration. Auerbach notices that the cells and fibres\napparent in the _plexus myentericus_ after an acid has been applied,\ncannot be detected before that application--nothing is visible but a\npale gelatinous network, with here and there knots of a paler hue;\nand I remember my surprise on examining the fresh spinal cord of a\nduck-embryo, and finding no trace of cells such as I had that very\nmorning seen in the cord of a chick of earlier date, but which had been\nsoaked in weak bichromate of potash. Now we have excellent grounds for\nbelieving that in both cases these organites were present, and that it\nwas the reagent which disclosed their presence in the chick; and so in\nother cases we must ask whether the forms which appear under a given\nmode of preparation are simply _unmasked_, or are in truth _produced_\nby the reagent? This question we can rarely answer.\n\nIf one of the very large cells be taken from the ganglion of a living\nmollusc, and be gently pressed till it bursts, the discharged contents\nwill be seen to be of a hyaline viscid substance, with fine granules\nbut no trace of fibres. Yet we must not rashly generalize from this,\nand declare that in the vertebrate cells the substance is not also\nfibrillated. As a good deal of speculation rests on the assumption of\nthe fibrillated cell-contents, I have thought it worth while to note\nthe uncertainty which hovers round it.\n\n122. Among the uncertainties must be reckoned the question as to the\ncell-processes. The existence of apolar and unipolar cells is flatly\ndenied by many writers, who assert that the appearances are due to the\nfragility of the processes. Fragile the processes are, and evidence\nof their having been broken off meet us in every preparation; but the\ndenial of apolar and unipolar cells seems to me only an example of\nthe tendency to substitute hypothesis for observation (\u00a7 114). The\n\u201cpostulate\u201d which some seem to regard as a \u201cnecessity of thought\u201d that\nevery nerve-cell shall have at least two fibres, one ingoing, the other\noutgoing, is allowed to override the plain evidence.[143] It originated\nin the fact first noticed by Wagner and Charles Robin that certain\ncells in the spinal ganglia of fishes are bipolar. The fact was rapidly\ngeneralized, in spite of its not being verified in _other_ places; the\ngeneralization was accepted because (by a strange process of reasoning\nrunning counter to all physiological knowledge) it was thought to\nfurnish an elementary illustration of the reflex process. As the centre\nhad its ingoing and outgoing nerve, so the cell was held to be a centre\n\u201cwrit small,\u201d and required its two fibres, No one paused to ask, how a\ncell placed in the _track_ of an ingoing nerve could fulfil this office\nof a reflex centre; no one supposed that the portion of the sensory\nfibre which continued its course, after the interruption of the cell,\nwas a motor fibre.\n\nWhat does Observation teach? It teaches that at first all nerve-cells\nare apolar. Even in the cortex of the cerebrum, where (unless we\ninclude the nuclei and grain-like corpuscles under cells) all the cells\nare finally multipolar, there is not one which has a process, up to\nthe seventh or eighth day of incubation (in the chick); from that day,\nand onwards, cells with one process appear; later on, cells with two,\nand later still, with three. By this time all the apolar cells have\ndisappeared. They may therefore be regarded as cells in their infancy.\nHowever that may be, we must accept the fact that apolar cells exist;\nwhether they can co-operate in neural functions, is a question which\nmust be decided after the mode of operation of cells is placed beyond a\ndoubt.\n\n123. If apolar cells are embryonic forms of cells which afterwards\nbecome multipolar, this interpretation will not suffice for the\nunipolar cells. They are not only abundant, but are mature forms in\nsome organs, and in some animals; though in some organs they may truly\nbe regarded as embryonic. Thus in the human embryo up to the fourth\nmonth all the cells of the spinal cord are said to be unipolar,[144]\nlater on they become multipolar. But in birds, rabbits, dogs, and\neven man, the cells in the spinal ganglia are mainly (if not wholly)\nunipolar;[145] nor is there any difficulty in observing the same fact\nin the \u0153sophageal ganglia of molluscs (see Fig.\u00a022).\n\nSuch are the observations. They have indeed been forced into agreement\nwith the bipolar postulate, by the assumption that the single process\nbranches into two, one afferent, the other efferent.[146] But before\nmaking observation thus pliant to suit hypothesis, it would be well to\nlook more closely into the evidence for the hypothesis itself. For my\nown part, I fail to see the justification of the postulate; whereas\nthe existence of unipolar cells is an observation which has been amply\nverified.\n\n[Illustration: Fig.\u00a018.--_Supposed union of two nerve-cells and a\nfibre._ The processes subdivide into a minute network, in which the\nfibre also loses itself.]\n\n124. Bipolar cells abound; multipolar cells are still more abundant;\nand these are the cells found in the gray substance of the neural\naxis. Deiters, in his epoch-making work,[147] propounded an hypothetic\n_schema_ which has been widely accepted. Finding that the large\ncells in the anterior horn of the spinal cord gave off processes\nof different kinds, one branched, the other unbranched, he held\nthat the latter process was the origin of the axis cylinder of\na nerve-fibre, whereas the branched process was protoplasm which\ndivided and subdivided, and formed the connection between one cell\nand another. Gerlach has modified this by supposing that the minute\nfibrils of the branching process reunite and form an axis cylinder\n(Fig.\u00a018). There is no doubt that some processes terminate in a fine\nnetwork; and there is a probability (not more) that the unbranched\nprocess is always continuous with the axis cylinder of a motor nerve,\nas we know it sometimes is with that of a dark-bordered fibre in the\nwhite substances. This, though probable, is, however, very far from\nhaving been demonstrated. Once or twice K\u00f6lliker, Max Schultze, and\nGerlach have followed this unbranched process as far as the _root_ of\na motor nerve; and they infer that although it could not be traced\nfurther, yet it did really join an axis cylinder there. In support\nOf this inference came the observations of Koschennikoff,[148] that\nin the cerebrum and cerebellum, processes were twice seen continuous\nwith dark-bordered nerve-fibres. But the extreme rarity of such\nobservations amid thousands of cells is itself a ground for hesitation\nin accepting a generalized interpretation, the more so since we have\nHenle\u2019s observation of the similar entrance of a _branched_ process\ninto the root.[149] Now it must be remembered that the branched process\nis by no anatomist at present regarded as the origin of the axis\ncylinder; so that if it can enter the root without being the origin of\na nerve-fibre, we are not entitled to assume that the entrance of the\nunbranched process has any other significance (on this head compare\n\u00a7 145), especially when we reflect that no trustworthy observer now\nprofesses to have followed a nerve-fibre of the posterior root right\ninto a multipolar cell. Figures, indeed, have been published which\nshow this, and much else; but such figures are diagrams, not copies of\nwhat is seen. They belong to Imaginary Anatomy.[150] The relation of\nthe cell-process to the nerve-fibre will be discussed anon.\n\n[Illustration:\n\n    Fig.\u00a019.--_Anastomosing nerve-cells_ (after Gratiolet). _a_, body\n    of the cell; _c_, process of uniting two cells; _d_, branching\n    process.\n]\n\n125. A word in passing on the contradictory assertions respecting\nthe anastomosis of nerve-cells. That the gray substance forms a\n_continuum_ of some kind is certain from the continuity of propagation\nof a stimulus. But it is by no means certain that one cell is directly\nunited to its neighbor by a cell-process. Eminent authorities assert\nthat such direct union never takes place; others, that it is a rare\nand insignificant fact; others, that it is constant, and \u201cdemanded by\nphysiological postulates.\u201d I will not, in the presence of distinct\naffirmations, venture to deny that such appearances as are presented\nin Fig.\u00a019 may occasionally be observed; the more so as I have myself\nseen perhaps half a dozen somewhat similar cases; but it is the opinion\nof Deiters and K\u00f6lliker that all such appearances are illusory.[151]\nGranting that such connections occur, we cannot grant this to be\nthe normal mode; especially now the more probable supposition is\nthat the connection is normally established by means of the delicate\nramifications of the branching processes.\n\nImaginary Anatomy has not been content with the cells of the anterior\nhorn being thus united together, to admit of united action, but has\ngone further, and supposed that the cells of the posterior horn,\nbesides being thus united, send off processes which unite them with\nthe cells of the anterior horn--and thus a pathway is formed for\nthe transmission of a sensory impression, and its conversion into a\nmotor impulse. What will the reader say when informed that not only\nhas no eye ever beheld such a pathway, but that the first step--the\ndirect union of the sensory nerve-fibre with a cell in the _posterior_\nhorn--is confessedly not visible?\n\n126. The foregoing criticisms will perhaps disturb the reader who has\nbeen accustomed to theorize on the data given in text-books; but he\nmay henceforward be more cautious in accepting such data as premises\nfor deduction, and will look with suspicion on the many theories which\nhave arisen on so unstable a basis. When we reflect how completely\nthe modern views of the nervous system, and the physiological,\npathological, and psychological explanations based on these views,\nare dominated by the current notions of the nerve-cell, it is of the\nlast importance that we should fairly face the fact that at present\nour knowledge even of the structure of the nerve-cell is extremely\nimperfect; and our knowledge of the part it plays--its anatomical\nrelations and its functional relations--is little more than guesswork!\n\n\nTHE NERVES.\n\n127. We now pass to the second order of organites; and here our\nexposition will be less troubled by hesitations, for although there is\nstill much to be learned about the structure and connections of the\nnerve-fibres, there is also a solid foundation of accurate knowledge.\n\n[Illustration:\n\n    Fig.\u00a020.--_a_, axis cylinder formed by the fibrils of the cell\n    contents, and at _a\u2019_ assuming the medullary sheath; _b_, naked\n    axis cylinder from spinal cord.\n]\n\nA nerve is a bundle of fibres within a membranous envelope supplied\nwith blood-vessels. Each fibre has also its separate sheath, having\nannular constrictions at various intervals. It is more correctly named\nby many French anatomists a nerve-_tube_ rather than a nerve-_fibre_;\nbut if we continue to use the term _fibre_, we must reserve it for\nthose organites which have a membranous sheath, and thereby distinguish\nit from the more delicate _fibril_ which has none.\n\nThe nerve tube or fibre is thus constituted: within the sheath\nlies a central band of neuroplasm identical with the neuroplasm of\nnerve-cells, and known as the _axis cylinder_; surrounding this band\nis an envelope of whitish substance, variously styled _myeline_,\n_medullary sheath_, and _white substance of Schwann_: it is closely\nsimilar to the chief constituent of the yolk of egg, and to its\npresence is due the whitish color of the fibres, which in its absence\nare grayish. The axis cylinder must be understood as the primary and\nessential element, because not only are there nerve-fibrils destitute\nboth of sheath and myeline yet fulfilling the office of Neurility,\nbut at their terminations, both in centres and in muscles, the\nnerve-fibres always lose sheath and myeline, to preserve only the\nneuroplasmic threads of which the axis cylinder is said to be composed.\nIn the lowest fishes, in the invertebrates, and in the so-called\nsympathetic fibres of vertebrates, there is either no myeline, or it is\nnot separated from the neuroplasm.\n\n128. Nerve-fibres are of two kinds--1\u00b0. The _dark-bordered_ or\n_medullary_ fibres, which have both sheath and myeline, as in the\nperipheral system; or only myeline, without the sheath, as in the\ncentral system. 2\u00b0. The _non-medullary_ fibres, which have the sheath,\nwithout appreciable myeline--such are the fibres of the olfactory, and\nthe pale fibres of the sympathetic.\n\nNerve-fibrils are neuroplasmic threads of extreme delicacy, visible\nonly under high magnifying powers (700\u2013800), which abound in the\ncentres, where they form networks. The fibrils also form the\nterminations of the fibres. Many fibrils are supposed to be condensed\nin one axis cylinder. This is represented by Max Schultze in Figs.\u00a017\nand 20.\n\n129. As may readily be imagined, the semi-liquid nature of the\nneuroplasm throws almost insuperable difficulties in the way of\naccurately determining whether the axis cylinder in the living nerve\nis fibrillated or not; whether, indeed, any of the aspects it presents\nin our preparations are normal. Authorities are not even agreed as\nto whether it is a pre-existent solid band of homogeneous substance,\nor a bundle of primitive fibrils, or a product of coagulation.[152]\nRudanowsky\u2019s observations on frozen nerves convinced him that the\ncylinder is a tubule with liquid contents.[153] My own investigations\nof the nerves of insects and molluscs incline me to the view of Dr.\nSchmidt of New Orleans, namely, that the cylinder axis consists\nof minute granules arranged in rows and united by a homogeneous\ninterfibrillar substance, thus forming a bundle of granular fibrils\nenclosed in a delicate sheath[154]--in other words, a streak of\nneuroplasm which has a fibrillar disposition of its granules. We ought\nto expect great varieties in such streaks of neuroplasm; and it is\nquite conceivable that in the Rays and the Torpedo there are axis\ncylinders which are single fibrils, and others which are bundles, with\nfinely granulated interfibrillar substance.[155]\n\nThe fibres often present a varicose aspect, as represented in Fig.\u00a021.\nIt is, however, so rarely observed in the fresh tissue, that many\nwriters regard it (as well as the double contour) as the product of\npreparation.[156] It is, indeed, always visible after the application\nof water.\n\nWe need say no more at present respecting the structure of\nnerve-fibres, except to point out that we have here an organite not\nless complex than the cell.\n\n[Illustration:\n\n    Fig.\u00a021.--_Nerve-fibres from the white substance of the cerebrum._\n    _a_, _a_, _a_, the medullar contents pressed out of the tube as\n    irregular drops.\n]\n\n\nTHE NEUROGLIA.\n\n130. Besides cells and fibres, there is the _amorphous substance_,\nwhich constitutes a great part of the central tissue, and also enters\nlargely into the peripheral tissue. It consists of finely granular\nsubstance, and a network of excessively delicate fibrils, with nuclei\ninterspersed. Its character is at present _sub judice_. Some writers\nhold it to be nervous, the majority hold it to be simply one of\nthe many forms of connective tissue: hence its name neuroglia, or\nnerve-cement.\n\nIn the convolutions of the frozen brain Walther finds the cells and\nfibres imbedded in a structureless semi-fluid substance wholly free\nfrom granules; the granules only appear there when cells have been\ncrushed. It is to this substance he attributes the fluctuation of\nthe living brain under the touch, like that of a mature abscess; the\nsolidity which is felt after death is due to the coagulation of this\nsubstance. Unhappily we have no means of determining whether the\nnetwork visible under other modes of investigation is present, although\ninvisible, in this substance. The neuroglia, as it appears in hardened\ntissues, must therefore be described with this doubt in our minds.\n\nIf we examine a bit of central gray substance where the cells and\nfibres are sparse, we see, under a low power, a network of fibrils\nin the meshes of which lie nerve-cells. Under very high powers we\nsee outside these cells another network of excessively fine fibrils\nembedded in a granular ground substance, having somewhat the aspect of\nhoar-frost, according to Boll. It is supposed that the first network\nis formed by the ultimate ramifications of the nerve-cell processes,\nand that the second is formed by ramifications of the processes of\n_connective_ cells. In this granular, gelatinous, fibrillar substance\nnuclei appear, together with small multipolar cells not distinguishable\nfrom nerve-cells except in being so much smaller. These nuclei are\nmore abundant in the tissue of young animals, and more abundant in the\ncerebellum than in the cerebrum. The granular aspect predominates the\nfresher the specimen, though there is always a network of fibrils; so\nthat some regard the granules as the result of a resolution of the\nfibrils, others regard the fibrils as the linear crystallization (so to\nspeak) of the granules.[157]\n\n131. Such is the aspect of the neuroglia. I dare not venture to\nformulate an opinion on the histological question whether this\namorphous substance is neural, or partly neural and partly connective\n(a substance which is potentially both, according to Deiters and\nHenle), or wholly connective. The question is not at present to be\nanswered decisively, because what is known as connective tissue has\nalso the three forms of multipolar cells, fibrils, and amorphous\nsubstance; nor is there any decisive mark by which these elements in\nthe one can be distinguished from elements in the other. The physical\nand chemical composition of Neuroglia and Neuroplasm are as closely\nallied as their morphological structure. And although in the later\nstages of development the two tissues are markedly distinguishable,\nin the early stages every effort has failed to furnish a decisive\nindication.[158] Connective tissue is dissolved by solutions which\nleave nerve-tissue intact. Can we employ this as a decisive test? No,\nfor if we soak a section of the spinal cord in one of these solutions,\nthe _pia mater_ and the membranous septa which ramify from it between\nthe cells and fibres disappear, leaving all the rest unaltered. This\nproves that Neuroglia is at any rate chemically different from ordinary\nconnective tissue, and more allied to the nervous. As to the _staining_\nprocess, so much relied on, nothing requires greater caution in its\nemployment. Stieda found that the same parts were sometimes stained and\nsometimes not; and Mauthner observed that in some cells both contents\nand nucleolus were stained, while the nucleus remained clear, in other\ncells the contents remained clear; and some of the axis cylinders were\nstained, the others not.[159] Lister found that the connective tissue\nbetween the fibres of the sciatic nerve, as well as the _pia mater_,\nwere stained like the axis cylinders;[160] and in one of my notes there\nis the record of both (supposed) connective cells and nerve-cells being\nstained alike, while the nerve-fibres and the (supposed) connective\nfibres were unstained. Whence I conclude that the supposition as to\nthe nature of the one group being different from that of the other was\nuntenable, if the staining test is to be held decisive.\n\n132. The histological question is raised into undue importance because\nit is supposed to carry with it physiological consequences which would\ndeprive the neuroglia of active co-operation in neural processes,\nreducing it to the insignificant position of a mechanical support. I\ncannot but regard this as due to the mistaken tendency of analytical\ninterpretation, which somewhat arbitrarily fastens on one element in a\ncomplex of elements, and assigns that one as the sole agent. Whether\nwe call the neuroglia connective or neural, it plays an essential part\nin all neural processes, probably a more important part than even the\nnerve-cells, which usurp exclusive attention! To overlook it, or to\nassign it a merely _mechanical_ office, seems to me as unphysiological\nas to overlook blood-serum, and recognize the corpuscles as the only\nnutrient elements. The notion of the neuroglia being a mere vehicle of\nsupport for the blood-vessels arises from not distinguishing between\nthe alimental and instrumental offices. In the function of a limb, bone\nis a co-operant. In the function of a centre, connective tissue is a\nco-operant; so that even if we acknowledge neuroglia to be a special\nform of connective tissue, it is an agent in neural processes; _what_\nits agency is, will be hereafter considered.\n\nFollowing Bidder and Kupffer, the Dorpat school proclaimed the whole\nof the gray substance of the posterior half of the spinal cord to\nbe connective tissue; and Blessig maintained that the whole of the\nretina, except the optic fibres, was connective tissue.[161] Even those\nanatomists who regarded this as exaggerated, admitted that connective\ntissue largely enters into the gray substance, especially if the\ngranular ground substance be reckoned as connective, the nerve-cells\nbeing very sparse in the posterior region. Be it so. Let us admit\nthat the gray matter of the frog\u2019s spinal cord is mainly composed of\nneuroglia, in which a very few multipolar nerve-cells are embedded.\nWhat must our conclusion be? Why, that since this spinal cord is\nproved to be a centre of energetic and manifold reflex actions--even\nto the extent of forcing many investigators to attribute sensation and\nvolition to it--this is proof that connective tissue does the work of\nnerve-tissue, and that the neuroglia is more important than nerve-cells!\n\nThree hypotheses are maintainable--1\u00b0. The neuroglia is the amorphous\nground-substance of undeveloped tissue (neuroplasm) out of which the\ncells and fibres of nerve-tissue and connective tissue are evolved.\n2\u00b0. It is the product of dissolved nerve cells and fibres. 3\u00b0. It is\nthe undeveloped stage of connective tissue. For physiological purposes\nwe may adopt any one of these views, provided we keep firm hold of the\nfact that the neuroglia is an essential element, and in the centres a\ndominant element. To make this clear, however, we must inquire more\nclosely into the relations of the three elements, nerve-cells, fibres,\nand neuroglia.\n\n\nTHE RELATIONS OF THE ORGANITES.\n\n133. In enumerating among the obstacles to research the tendency to\nsubstitute hypothetic deductions in place of objective facts, I had\nspecially in my mind the wide-reaching influence of the reigning\ntheories of the nerve-cell. Had we a solidly established theory of the\ncell, equivalent, say, to our theory of gas-pressure, we should still\nneed caution in allowing it to override exact observation; but insecure\nas our data are, and hypothetical as are the inferences respecting\nthe part played by the cell, the reliance placed on deductions from\nsuch premises is nothing less than superstition. Science will take a\nnew start when the whole question is reinvestigated on a preliminary\nsetting aside of all that has been precipitately accepted respecting\nthe office of the cell. This exercise of the imagination, even should\nthe reigning theories subsequently be confirmed, would not fail to\nbring many neglected facts into their rightful place.\n\nI am old enough to remember when the cell held a very subordinate\nposition in Neurology, and now my meditations have led me to return, if\nnot to the old views of the cell, at least to something like the old\nestimate of its relative importance. Its existence was first brought\nprominently forward by Ehrenberg in 1834, who described its presence in\nthe sympathetic ganglia; and by Remak in 1837, who described it in the\nspinal ganglia. For some time afterwards the ganglia and centres were\nsaid to contain irregular masses of vesicular matter which were looked\non as investing the fibres; what their office was, did not appear. But\nthere rapidly arose the belief that the cells were minute batteries\nin which \u201cnerve-force\u201d was developed, the fibres serving merely as\nconductors. Once started on this track, Hypothesis had free way, and a\nsort of fetichistic deification of the cell invested it with miraculous\npowers. In many works of repute we meet with statements which may\nfitly take their place beside the equally grave statements made by\nsavages respecting the hidden virtues of sticks and stones. We find\nthe nerve-cells credited with \u201cmetabolic powers,\u201d which enable them\nto \u201cspiritualize impressions, and materialize ideas,\u201d to _transform_\nsensations into movements, and _elaborate_ sensations into thoughts;\nnot only have they this \u201cremarkable aptitude of metabolic local\naction,\u201d they can also \u201cact at a distance.\u201d[162] The savage believes\nthat one pebble will cure diseases, and another render him victorious\nin war; and there are physiologists who believe that one nerve-cell has\nsensibility, another motricity, a third instinct, a fourth emotion, a\nfifth reflexion: they do not say this in so many words, but they assign\nto cells which differ only in size and shape, specific qualities. They\ndescribe sensational, emotional, ideational, sympathetic, reflex, and\nmotor-cells; nay, Schr\u00f6der van der Kolk goes so far as to specify\nhunger-cells and thirst-cells.[163] With what grace can these writers\nlaugh at Scholasticism?\n\n134. The hypothesis of the nerve-cell as the fountain of nerve-force\nis supported by the gratuitous hypothesis of cell-substance having\ngreater chemical tension and molecular instability than nerve-fibre.\nNo evidence has been furnished for this; indeed the only experimental\nevidence bearing on this point, if it has any force, seems directly\nadverse to the hypothesis. I allude to the experiments of Wundt, which\nshow that the faint stimulus capable of moving a muscle when applied\ndirectly to its nerve, must be increased if the excitation has to pass\nthrough the cells by stimulation of the sensory nerve.[164] Wundt\ninterprets this as proving that the cells retard every impulse, whereby\nthey are enabled to store up latent force. The cells have thus the\noffice of locks in a canal, which cause the shallow stream to deepen at\nparticular places. I do not regard this interpretation as satisfactory;\nbut the fact at any rate seems to prove that so far from the cells\nmanifesting greater instability than the fibres, they manifest less.\n\n135. The hypothesis of nerve-force being developed in the ganglia,\ngradually assumed a more precise expression when the nerve-cells were\nregarded as the only important elements of a ganglion. It has become\nthe foundation-stone of Neurology, therefore very particular care\nshould be taken to make sure that this foundation rests on clear and\nindisputable evidence. Instead of that, there is absolutely no evidence\non which it can rest; and there is much evidence decidedly opposed to\nit. Neither structure nor experiment points out the cells as the chief\nagents in neural processes. Let us consider these.\n\nFig.\u00a022 shows the contents of a molluscan ganglion which has been\nteased out with needles.\n\n[Illustration: Fig.\u00a022.--_Cells, fibres, and amorphous substance from\nthe ganglion of a mollusc_ (after Bucholtz).]\n\nThe cells are seen to vary in size, but in all there is a rim of\nneuroplasm surrounding the large nucleus, and from this neuroplasm\nthe fibre is seen to be a prolongation. The dotted substance in the\ncentre is the neuroglia. Except in the possession of a nucleus, there\nis obviously here no essential difference in the structure of cell and\nfibre.\n\n[Illustration:\n\n    Fig.\u00a023--_Fibres from the auditory nerve._ _a_, the axis cylinder;\n    _b_, the cellular enlargement; _c_, the medullary sheath.\n]\n\nNow compare this with Fig.\u00a023, representing three fibres from the\nauditory nerve.\n\n\nHere the cell substance, as Max Schultze remarks, \u201cis a continuation\nof the axis cylinder, and encloses the nucleus. The medulla commonly\nceases at the point where the axis enters the cell, to reappear at its\nexit; but it sometimes stretches across the cell to enclose it also:\nso that such a ganglion cell is in truth simply the nucleated portion\nof the cylinder axis.\u201d[165] There are many places in which fibres are\nthus found with cells inserted in their course as swellings: in the\nspinal ganglia of fishes these are called bipolar cells; they are\nsometimes met with even in the cerebellum; but oftener in peripheral\nnerves, where they are mostly small masses of granular neuroplasm\nfrom which usually a branching of the fibre takes place. The point\nto which attention is called is that in some cases, if not in all,\nthe nerve-fibre is structurally continuous with the cell contents.\nThe two organites--fibre and cell--differ only as regards the nucleus\nand pigment. Haeckel, who affirms that in the crayfish (_Astacus\nfluviatilis_) he never saw a cell which did not continue as a fibre,\nthinks there is always a marked separation of the granular substance\nfrom its \u201chyaline protoplasm,\u201d and that only this latter forms the axis\ncylinder. But although my observations agree with this as a general\nfact, I have seen even in crayfish the granular substance prolonged\ninto the axis cylinder; and in other animals the granular substance is\nfrequently discernible.\n\nIndeed it may be said that anatomists are now tolerably unanimous as to\nthe axis cylinder being identical with the protoplasmic cell substance.\nIf this be so, we have only to recall the principle of identity of\nproperty accompanying identity of structure, to conclude that _whatever\nproperties we assign to the cells_ (unless we restrict these to the\nnucleus and pigment) _we must assign to the axis cylinders_. We can\ntherefore no longer entertain the hypothesis of the cells being the\nfountains or reservoirs of Neurility; the less so when we reflect that\ncells do not form the hundredth part of nerve-tissue: for even the\ngray substance bears but a small proportion to the white; and of the\ngray substance, Henle estimates that one half is fibrous, the rest is\npartly cellular, partly amorphous. Those who derive Neurility from\nthe cells, forget that although the organism begins as a cell, and\nfor some weeks consists mainly of cells, yet from this time onwards\nthere is an ever-increasing preponderance of cell-derivatives--fibres,\ntubes, and amorphous substance--and corresponding with this is the\never-increasing power and complexity of the organism.\n\n136. From another point of view we must reject the hypothesis. Not\nonly does the evidence which points to the essential continuity in\nstructure of nerve cell and fibre discredit the notion of their\nphysiological diversity, but it is further supported by the fact\nthat although the whole nervous system is structurally continuous,\nan immense mass of nerve-fibres have no _immediate_ connection with\nganglionic cells:--neither springing from nor terminating in such\ncells, their activity cannot be assigned to them. To many readers this\nstatement will be startling. They have been so accustomed to hear\nthat every fibre begins or terminates in a cell, that a doubt thrown\non it will sound paradoxical. But there is an equivoque here which\nmust be got rid of. When it is said that every fibre has its \u201corigin\u201d\nin a cell, this may be true if origin mean its _point of departure\nin evolution_, for \u201ccells\u201d are the early forms of all organites;\nbut although every organite is at first a cell, and in this sense a\nnerve-fibre must be said to originate in a cell, we must guard against\nthe equivoque which arises from calling the highly differentiated\norganite, usually designated ganglionic cell, by the same name as\nits starting-point. On this ground I suggest the term neuroblast, in\nlieu of nerve-cell, for the earlier stages in the evolution of cell\nand fibre. Both Embryology and Anatomy seem to show that cell and\nfibre are organites differentiated from identical neuroblasts, with a\nsomewhat varying history, so that in their final stages the cell and\nfibre have conspicuous differences in form with an underlying identity;\njust as a male and female organism starting from identical ova, and\nhaving essential characters in common, are yet in other characters\nconspicuously unlike. The multipolar cell is not necessarily the origin\nof a nerve-fibre, although it is probable that some short fibres\nhave their origin in the prolongations of cells. Although the latter\npoint has not, I think, been satisfactorily established, except in the\ninvertebrata, I see no reason whatever to doubt its probability; what\nseems the least reconcilable with the evidence is the notion that all\nfibres arise as prolongations from ganglionic cells, instead of arising\nindependently as differentiations from neuroblasts. The reader will\nobserve that my objection to the current view is purely anatomical; for\nthe current view would suit my physiological interpretations equally\nwell, and would be equally irreconcilable with the hypothesis of the\ncell as the source of Neurility, so long as the identity of structure\nin the axis cylinder and cell contents is undisputed.\n\n137. The evidence at present stands thus: There are numerous multipolar\ncells which have no traceable connection with nerve-fibres; and fibres\nwhich have no direct connection with multipolar cells. By the first\nI do not mean the disputed apolar cells, I mean cells in the gray\nsubstance of the centres which send off processes that subdivide and\nterminate as fibrils in the network of the Neuroglia (Figs.\u00a016, 18).\nIt is indeed generally assumed that these have each one process--the\naxis-cylinder process--which is prolonged as a nerve-fibre; nor would\nit be prudent to assert that such is never the case; though it would\nbe difficult to distinguish between a fibre which had united with a\nprocess and a fibre which was a prolongation of a process, in both\ncases the neuroplasm being identical. I only urge that the assumption\nis grounded not on anatomical evidence, but on a supposed necessary\npostulate. All that can be demonstrated is that some processes\nterminate in excessively fine fibrils; and occasionally in thousands\nof specimens processes have been traced into dark-bordered fibres.\nIt is true that they often present appearances which have led to\nthe inference that they did so terminate--appearances so deceptive\nthat Golgi and Arndt independently record observations of unbranched\nprocesses having the aspect of axis cylinders being prolonged to\na considerable distance (600 \u03bc in one case), yet these were found\nto terminate _not_ in a dark-bordered fibre, but in a network of\nfibrils.[166]\n\n138. While it is thus doubtful whether dark-bordered fibres are always\nimmediately connected with cells, it is demonstrable that multitudes\nof fibres have only an indirect connection with cells, being developed\nas outgrowths from other fibres. Dr. Beale considers that in each\nsuch outgrowths have their origin in small neuroplasmic masses (his\n\u201cgerminal matter\u201d). That is another question. The fact here to be\ninsisted on is that we often find groups of cells with only two or\nthree fibres, and groups of fibres where very few cells exist. Schr\u00f6der\nvan der Kolk says that in a sturgeon (_Accipenser sturio_) weighing 120\npounds he found the spinal cord scarcely thicker than that of a frog;\nthe muscles of this fish are enormous, and its motor nerves abundant;\nyet these nerves entered the cord by roots no thicker than a pig\u2019s\nbristle; and in the very little gray matter of the cord there was only\na cell here and there found after long search. Are we to suppose that\nthese rare cells were the origins of all the motor and sensory nerves?\nA similar want of correspondence may be noticed elsewhere. Thus in the\nspinal cord of the Lamprey my preparations show very few cells in any\nof the sections, and numerous sections show none at all. Stieda counted\nonly eight to ten cells in each horn of some osseous fishes, except\nat the places where the spinal roots emerged. In the eel and cod he\nfound parts of the cord quite free from cells, and in other parts found\ntwo, three, never more than ten. In birds he counted from twenty-five\nto thirty. Particular attention is called to this fact of the eel\u2019s\ncord being thus deficient, because every one knows the energetic\nreflex action of that cord, each separate segment of which responds to\nperipheral stimulation.\n\nIt may indeed be urged that these few cells were the origin of all\nthe fibres, the latter having multiplied by the well-known process of\nsubdivision; and in support of this view the fact may be cited of the\ncolossal fibres of the electric fishes, each of which divides into\nfive-and-twenty fibres, and in the electric eel each fibre is said\nby Max Schultze to divide into a million of fibrils. But I interpret\nthis fact otherwise. It seems to me to prove nothing more than that\nthe neuroplasm has differentiated into few cells and many fibres.\nAnd my opinion is grounded on the evidence of Development, presently\nto be adduced. If we find (and this we do find) fibres making their\nappearance anywhere _before_ multipolar cells appear, the question is\nsettled.\n\n139. Dr. Beale regards the large caudate cells of the centres as\ndifferent organites from the oval and pyriform cells, and thinks they\nare probably stations through which fibres having different origins\nmerely pass, and change their directions; and Max Schultze says that\nno single fibril has been found to have a central origin; every fibril\narises at the periphery, and passes through a cell, which is thus\ncrossed by different fibrils.[167] (Comp. Fig.\u00a017.)\n\nThe teaching of Development is on this point of supreme importance.\nUnhappily there has not yet been a sufficient collection of systematic\nobservations to enable us to speak very confidently as to the\nsuccessive stages, but some negative evidence there is. The changes\ntake place with great rapidity, and the earliest stages have hardly\nbeen observed at all. Although for several successive years I watched\nthe development of tadpoles, the difficulties were so great, and the\nappearances so perplexing, that the only benefit I derived was that of\nbeing able the better to understand the more successful investigations\nof others. Four or five days after fecundation is the earliest period\nof which I have any recorded observation; at this period the cerebral\nsubstance appeared as a finely granular matter, having numerous lines\nof segmentation marking it off into somewhat spherical and oval masses,\ninterspersed with large granules and fat globules. Here and there\nhyaline substance appeared between the segments. Similar observations\nhave since been recorded by Charles Robin in the earliest stages\nof the Triton.[168] He says that when the external gills presented\ntheir first indications, nuclei appeared, each surrounded by a rim of\nhyaline substance, from which a pale filament was prolonged at one end,\nsometimes one at both ends, and this filament subdivided as it grew\nin length until it had all the appearance of an axis cylinder. This,\nhowever, he says, is a striation, not a fibrillation; he refuses to\nadmit that the axis cylinder is a bundle of fibrils. He further notices\nthe simultaneous appearance of amorphous substance; and as this is\nseveral days before there is any trace of a _pia mater_, or proper\nconnective tissue, he urges this among the many considerations which\nshould prevent the identification of neuroglia with connective tissue.\n\nIn a very young embryo of a mole (I could not determine its age) the\ncortex of the hemispheres showed granular amorphous substance, in\nwhich were embedded spherical masses of somewhat paler color, which\nhad no nuclei, and were therefore not cells. Besides these, there were\nnucleated masses (apolar cells, therefore) and more developed cells,\nunipolar, bipolar, and tripolar. Not a trace of a nerve-fibre was\nvisible. In agreement with this are the observations of Masius and Van\nLair, who cut out a portion of the spinal cord in a frog, and observed\nthe regenerated tissue after the lapse of a month. It contained apolar,\nbipolar, and multipolar cells, together with \u201ccorpuscles without\nprocesses, for the most part larger than the cells, and appearing to be\nmere agglomerations of granules,\u201d--these latter I suppose to have been\nwhat I describe as segmentations of the undeveloped substance. Gray\nfibres, with a few varicose fibres, also appeared.[169]\n\n140. The admirable investigations of Franz Boll have given these\nobservations a new significance. He finds in the cerebral substance\nof the chick on the third or fourth day of incubation a well-marked\nseparation between the neuroglia and nerve-tissue proper. Fig.\u00a024, A,\nrepresents three nerve-cells, each with its nucleus and nucleolus,\nand each surrounded with its layer of neuroplasm. The other four\nmasses he regards as nuclei of connective tissue. Three days later the\ndistinction between the two is more marked (Fig.\u00a024, B). Not only have\nthe nerve-cells acquired an increase of neuroplasm, they also present\nindications of their future processes, which at the twelfth day are\nvaricose (Fig.\u00a024, C). (All this while the connective corpuscles remain\nunchanged.) Although Boll was unable to trace one of these processes\ninto nerve-fibres, he has little doubt that they do ultimately become\n(unite with?) axis cylinders.\n\n[Illustration: Fig.\u00a024.--_Embryonic nerve-cells._]\n\n[Illustration: Fig.\u00a025.--_Embryonic nerve-fibres._]\n\nIt is difficult to reconcile such observations with the hypothesis of\nthe cells being simply points of _reunion of fibrils_. We see here\nmultipolar cells before any fibrils appear. Respecting the development\nof the white substance, i.\u00a0e. the nerve-fibres, Boll remarks that in\nthe _corpus callosum_ of the chick the first differentiation resembles\nthat of the gray substance.\n\nThe polygonal and spindle-shaped cells represented in Fig.\u00a025, A, are\nrespectively starting-points of connective and neural tissues. The\nspindle-shaped cells elongate, and rapidly become bipolar. This is\nsupposed to result in the whole cell becoming transformed into a fibre,\nthe nucleus and nucleolus vanishing; but the transformation is so rapid\nthat he confesses that he was unable to trace its stages; all that can\npositively be asserted is that one or two days after the appearance\npresented in Fig.\u00a025, B, the aspect changes to that of fibrils. The\ncolumns of polygonal cells between which run these fibrils, he regards\nas the connective corpuscles described by several anatomists in the\nwhite substance both of brain and cord, and which are sometimes\ndeclared to be multipolar nerve-cells.[170]\n\n141. Dr. Schmidt\u2019s observations on the human embryo were of course\non tissue at a very much later stage. According to him, the fibrils\nof the axis cylinders are formed by the linear disposition and\nconsolidation of elementary granules. The fibrils thus formed are\nseparated by interfibrillar granules which in time become fibrils. Not\nearlier than three months and a half does the formation of individual\naxis cylinders begin by the aggregation of these fibrils into minute\nbundles, which are subsequently surrounded by a delicate sheath.[171]\n\n142. With respect to the transition of the spindle-shaped cells into\nfibrils, since there is a gap in the observations of Boll, and since\nthose of Schmidt are subsequent to the disappearance of the cells,\nand in both cases all trace of nucleus has disappeared, I suggest\nthat we have here an analogy with what Weismann has recorded of the\nmetamorphoses of insects. In the very remarkable memoir of that\ninvestigator[172] it is shown that the metamorphoses do not take place\nby a gradual modification of the existing organs and tissues, but by a\n_resolution_ of these into their elements, and a _reconstruction_ of\ntheir elements into tissues and organs. The muscles, nerves, trache\u00e6,\nand alimentary canal, undergo what may be called a fatty degeneration,\nand pass thence into a mere blastema. _It is out of these ruins of the\nold tissues that the new tissues are reconstructed._ On the fourth day\nthe body of the pupa is filled with a fluid mass--a plasma composed of\nblood and dissolved tissues. The subsequent development is thus in all\nessential respects a repetition of that which originally took place in\nthe ovum.[173]\n\nTwo points are especially noticeable: First, that in this resolved\nmass of granules and fat globules there quickly appear large globular\nmasses which develop a fine membrane, and subsequently nuclei. A glance\nat the figure 51 of Weismann\u2019s plates reveals the close resemblance to\nthe earliest stages of nerve-cells; and the whole process recalls the\nregeneration of nerves and nerve-centres after their fatty degeneration.\n\nSecondly, the nerves reappear in their proper places in the new\nmuscles, and this at a time when the nerve-centres are still unformed;\nso that the _whole peripheral system is completely rebuilt in absolute\nindependence of the central system_. The idea, therefore, that\nnerve-fibres are the products of ganglia must be relinquished. This\nidea is further discountenanced by Boll\u2019s observations, which show that\nthe fibre-cells are from the first different from the ganglionic cells;\nand by the observations of Foster and Balfour, that \u201cfibres are present\nin the white substance on the third day of incubation\u201d; _whereas cell\nprocesses do not appear until the eighth day_. Foster and Balfour are\ninclined to believe \u201cthat even on the seventh day it is not possible\nto trace any connection between the cells and fibres.\u201d In the later\nstages, the connection is perhaps established.[174]\n\n143. We may, I think, conclude from all this that in the higher\nvertebrates the white substance of brain and cord is not the direct\nproduct of the gray substance; in other words, that here nerve-fibres,\neven if subsequently in connection with the ganglionic cells, have\nan independent origin. They may grow towards and blend with cell\nprocesses; they are not prolongations of those processes. They may be\nidentical in structure and property, as one muscle is identical with\nanother, but one is not the parent of the other.\n\n144. Sigmund Mayer emphatically declares that in no instance has he\ntraced a cell process developed into a dark-bordered nerve-fibre.\nThe process, he says, may often be traced for a certain distance\nalongside of a fibre; but it then suddenly ceases, whereas the fibre\nis seen continuing its course unaltered. Still more conclusive is the\nevidence afforded by nerves having only very few fibres (2\u20134 sometimes\nin the frog), which have, nevertheless, a liberal supply of cells,\nvisible without preparation. Valentin counted twenty-four cells in a\nnerve which had but two fibres.[175] Now although it is possible to\nexplain the presence of numerous fibres with rare cells either as due\nto subdivisions of fibres, or to the fibres having cells elsewhere\nfor their origin, it is not thus that we can explain the presence of\nnumerous cells which have no fibres developed from their processes.\n\n145. With regard to this observation of the cell process running\nalongside of the fibre, the recent researches of Ranvier may throw\nsome light on it. He describes the cells in the spinal ganglia as all\nunipolar; each single process pursues a more or less winding course\nas a fibril, often blending with others, till it reaches one of the\nfibres from the sensory root. It blends with this fibre at the annular\nconstriction of the fibre, becoming here incorporated with it, so that\na T-shaped fibre is the result.[176] If this should be confirmed, it\nwould reconcile many observations; but it would greatly disturb all\ncurrent interpretations. Ranvier remarks that it is no longer tenable\nto suppose that the ganglionic cell is a centre, sensory or motor,\nreceiving the excitation or sending forth a motor impulse; for if the\nfibril issuing from a cell becomes laterally soldered to a nerve-fibre,\nthere is no possibility of saying in which direction this cell receives\nthe excitation, nor in which it transmits the impulse.\n\n146. We have seen good reason to conclude that the essential element of\nthe nerve--the axis cylinder--is the same substance as the neuroplasm\nwhich forms the essential element of the cell. At any rate, we are\nquite certain that the cell process is neuroplasm. On this ground there\nis no difficulty in understanding that a cell process may sometimes be\ndrawn out into an axis cylinder (as indeed we see to be the case in\nthe invertebrata and electric fishes); while again in numerous other\ncases the nerve-fibre has an independent origin, being, in short, a\ndifferentiation from the neuroplasm which has become a fibre instead\nof a cell. It is clear from the observations of Rouget on Development,\nand of Sigmund Mayer on Regeneration, that fibres, nuclei, and cells\nbecome differentiated from the same neuroplasm, those portions which\nare not converted into fibres remaining first as lumps of neuroplasm,\nthen acquiring a nucleus, and some of these passing into cells. I mean\nthat between fibres, nuclei, and cells there are only morphological\ndifferences in an identical neuroplasm.[177] If this is in any degree\ntrue, it will not only explain how fresh fibres may be developed in the\ncourse of fibres, branching from them as from trunks, and branchlets\nfrom branchlets, twigs from branchlets, the same conditions of growth\nbeing present throughout; it will also completely modify the notion\nof any physiological distinction between cell and fibre greater than\ncan be assigned to the morphological differences. We shall then no\nlonger suppose that the cell is the fountain whence the fibre draws its\nnutrition and its \u201cforce\u201d; and this will be equally the case even if we\nadmit that a cell is, so to speak, the germ from which a whole plexus\nof fibres was evolved, for no one will pretend that the \u201cforce\u201d of an\norganism is directly derived from the ovum, or that the ovum nourishes\nthe organism.\n\n147. At this stage of the discussion it is needful to consider a point\nwhich will spontaneously occur to every instructed reader, I mean the\ninteresting fact discovered by Dr. Waller, that when a sensory root was\ndivided, the portion which was still in connection with the ganglion\nremained unaltered, whereas the portion which was only in connection\nwith the spinal cord degenerated; and _vice versa_, when a motor root\nwas divided, the portion connected with the cord remained unaltered,\nthe portion severed from the cord degenerated. The observation has\nbeen frequently confirmed, and the conclusion drawn has been that the\ncells in the ganglion of the posterior root are the nutritive centres\nof posterior nerves, the cells in the anterior horn of the cord being\nthe nutritive centres of the anterior nerves. Another interpretation\nis however needed, the more so because the fact is not constant.[178]\nTrue of some nerves, it is not true of others. Vulpian found that\nwhen he cut out a portion of the lingual nerve, and transplanted\nit by grafting under the skin of the groin, where of course it was\nentirely removed from all ganglionic influence, it degenerated, but it\nalso regenerated. Pathological observations convinced Meissner that\nthe ganglia are wholly destitute of an influence on the nutrition of\nthe vagus; and Schiff proved experimentally that other ganglia were\nequally inoperative, since motor nerves could be separated from the\nspinal cord without degeneration.[179] Not however to insist on this,\nnor on the other facts of regeneration, in the absence of ganglionic\ninfluence, let us remark that Dr. Waller\u2019s examples would not be\nconclusive unless the teaching of Embryology could be disproved. That\nnerves degenerate when separated from ganglia is a fact; but it is also\na fact that muscles degenerate when separated from a nerve-centre; yet\nwe do not suppose the nerve-centre to nourish the muscles. And against\nthe fact that the sensory nerve remains unaltered only in that portion\nwhich is connected with the ganglion, we must oppose the observations\nof K\u00f6lliker and Schwalbe,[180] who affirm that none of the fibres\nwhich enter the posterior columns of the spinal cord have any direct\nconnection with the cells of the ganglion on the posterior root. The\ncells of this ganglion they declare to be unipolar (in the higher\nvertebrates), and the fibres in connection with these cells are not\nthose which pass to the cord, but all of them pass to the periphery.\nAccording to Ranvier, the fibres from the cells join the fibres of\nthe posterior root. Schwalbe found that if the spinal nerve be firmly\ngrasped and _steadily_ drawn, it will often be pulled from its sheath,\nand the ganglion laid bare;[181] in this ganglion all the cells are\nfound undisturbed, which could not be the case had fibres from _those_\ncells entered the cord, since the traction would necessarily have\ndisturbed them.\n\n\nRECAPITULATION.\n\n148. At the opening of this chapter mention was made of the besetting\nsin of the analytical tendency, namely, to disregard the elements\nwhich provisionally had been set aside, and not restore them in the\nreconstruction of a synthetical explanation. Familiar experiences\ntell us that a stimulus applied to the skin is followed by a muscular\nmovement, or a glandular secretion; sometimes this takes place without\nany conscious sensation; sometimes we are distinctly conscious of\nthe stimulus; and sometimes we consciously will the movement. These\nfacts the physiologist tries to unravel, and to trace the complicated\nprocesses involved. The neurologist of course confines himself\nexclusively to the neural processes; all the other processes are\nprovisionally left out of account. But not only so: the analytical\ntendency is carried further, and even in the neural process the\n_organs_ are neglected for the sake of the nervous _tissue_, and the\nnervous tissue for the sake of the _nerve-cell_. The consequence has\nbeen that we have an explanation offered us which runs thus:--\n\n149. The nerve-cell is the supreme element, the origin of the\nnerve-fibre, and the fountain of nerve-force. The cells are connected\none with another by means of fibres, and with muscles, glands, and\ncentres also by means of fibres, which are merely channels for the\nnerve-force. A stimulus at the surface is carried by a sensory fibre\nto a cell in the centre; from that point it is carried by another\nfibre to another cell; and from that by a third fibre to a muscle:\na reflex contraction results. This is the elementary \u201cnervous arc.\u201d\nBut this arc has also higher arcs with which it is in connection: the\nsensory cell besides sending a fibre directly to a motor cell, also\nsends one upwards to the cerebral centres; and here again there is a\nnervous arc, so that the cerebral centre sends down an impulse on the\nmotor cells, and the contraction which results is due to a volitional\nimpulse. The transmission of the stimulation which in the first case\nwas purely physical, becomes in the latter case psychical. The sensory\nimpression is in one cell transformed into a _sensation_, in another\ncell into an _idea_, in a third cell into a _volition_.\n\n150. This course is described with a precision and a confidence which\ninduces the inexperienced reader to suppose that it is the transcript\nof actual observation. I venture to say that it is imaginary from\nbeginning to end. I do not affirm that no such course is pursued,\nI only say no such course was ever demonstrated, but that at every\nstage the requisite facts of observation are either incomplete or\ncontradictory. First, be it noted that the actions to be explained are\nnever the actions of organs so simple as the description sets forth.\nIt is not by single fibres and cells that the stimulus is effected,\nbut by complex nerves and complex centres. Only by a diagrammatic\nartifice can the fibre represent the nerve, and the cell the centre.\nIn reality the cells of the centre (supposing them to be the _only_\nagents) act in groups, and Anatomy should therefore show them to be\nmutually united in groups--which is what no Anatomy has succeeded in\nshowing, unless the Neuroglia be called upon. Secondly, be it noted\nthat the current scheme of the relations between cells and fibres is\none founded on physiological postulates, not on observation. Thirdly,\nmuch of what is actually observed is very doubtful, because we do not\nknow whether the appearances are normal, or due to modes of preparation\nand post-mortem changes. We cannot at present say, for instance,\nwhether the fibrillated appearance of cell contents and axis cylinder\nrepresents the living structure or not. We may either suppose that\nthe neuroplasmic pulp splits longitudinally into fibres, or that\nneuroplasmic threads resolve themselves into a homogeneous pulp--the\naxis cylinder may be a condensation of many fibrils, or the fibrils may\nbe a resolution of the substance.\n\n151. Let us contrast step by step the Imaginary Anatomy found in the\ntext-books with the Objective Anatomy as at present disclosed by the\nresearches of all the chief workers. Imaginary Anatomy assumes that the\nsensory fibre passes from a surface into the cells of the posterior\nhorn of the spinal cord. Objective Anatomy sees the fibre pass into the\ngray substance, but declares that no direct entrance of a fibre into a\ncell is there visible.\n\nImaginary Anatomy assumes that from the sensory cells of the gray\nsubstance pass fibres in connection with the motor cells of the\nanterior horn, thus forming a direct channel through which the\nexcitation of a sensory cell is transmitted to a motor cell. Objective\nAnatomy fails to discover any such direct channel--no such fibres are\ndemonstrable.\n\nImaginary Anatomy assumes that from the motor cells issue fibres which\ndescend to the muscles and glands, and carry there the motor impulses\nand the \u201cmandates of the will.\u201d Objective Anatomy fails to find at\nthe utmost more than a probability that these cells are continued\nas fibres, a probability which is founded on the rare facts of cell\nprocesses having been seen extending into the roots of the nerves, and\nof a cell process having occasionally been seen elsewhere continuous\nwith a dark-bordered fibre. Granting, however, that this probability\nrepresents the fact, we have thus only one part of the \u201cnervous arc\u201d\nwhich can be said to have been verified.\n\nImaginary Anatomy further assumes that this nervous arc is connected\nwith cerebral centres by means of fibres going upwards from the\nposterior cells, and fibres descending downwards to the anterior\ncells. Objective Anatomy sees nothing of the kind. It sees fibres\nentering the gray substance, and there lost to view in a mass of\ngranular substance, fibrils, neuroblasts, and cells. There _may\nbe_ uninterrupted fibres passing upwards and downwards; but it\nis impossible to see them. And if we are told that physiological\ninterpretations demand such a structure, we may fairly ask if this, and\nthis only, is the structure which is adequate to the propagation of\nexcitation? Now it seems to me that another kind of structure, and one\nmore closely agreeing with what is observed, better answers the demands\nof Physiology. This will be more evident after the Laws of Nervous\nAction have been expounded in the succeeding chapter. Meanwhile we may\nremark that the arrangement of cells and fibres which is imagined as\nthe mechanism of propagation and reflexion is absolutely irreconcilable\nwith the teaching of Experiment: for the spinal cord may be cut through\nanywhere, without destruction of the transmission of sensory and motor\nexcitations, provided only a small portion of gray substance be left to\nestablish the continuity of the axis. Divide all the substance of the\nposterior half in one place, and all the substance of the anterior half\nin another, yet so long as there is a portion of gray substance left\nas a bridge between the lower and upper segments, the transmission of\nsensory and motor excitations will take place.\n\n152. In other essential respects we have to note that the anatomical\nevidence for the current interpretations is absolutely deficient or\ncontradictory. There is no adequate warrant for the assumption that all\nnerves have their origin in ganglia, all fibres in cells. Such evidence\nas at present exists is against that supposition, and in favor of the\nsupposition that both cell and fibre are differentiations of a common\nneuroplasm, sometimes directly, sometimes indirectly continuous.\nFibres, and plexuses of fibres, interspersed with cells irregularly\ndistributed--now singly, now in small groups, now in larger and larger\ngroups--constitute the _figured_ elements of nerve-tissue; and even if\nwe set aside the _amorphous_ substance as indifferent or subordinate,\nwe have still no ground for assigning the supremacy, much less the sole\nsignificance, to the cells. The grounds of this denial have been amply\nfurnished in our exposition. For, let it be granted that nerve-cells\nare the origins of the fibres and the sources of their nutrition--a\npoint which is eminently disputable--this would in no sense help the\nphysiological hypothesis of the cell as the fountain of Neurility. If\nthe fibre is simply the cell-contents drawn out longitudinally, if\nits essential element is identical with the essential element of the\ncell, then we can no more ascribe to the cell the exclusive property\nof Neurility than we can draw a lump of lead out into a wire, and then\nascribe different properties to the thin end and the thick end. But\non this point it is needless to speculate, since we have experimental\nevidence proving that the nerve-fibre has its Neurility even when\nseparated from the cell, or even from the ganglion.\n\n153. It is possible--I do not see sufficient evidence for a stronger\nassertion--that the cells are the nutritive sources of the fibres. They\nmay represent the alimental rather than the instrumental activities of\nnervous life. (Compare PROBLEM I. \u00a7 42.) My contention is that in any\ncase they are not the supreme elements of the active tissue, and in no\nsense can they be considered as _organs_. Only confusion of ideas could\nfor a moment permit such language, or could assign central functions\nto cells which are elements of tissue. If the cell be credited with\nsuch powers anywhere, it must be credited with them everywhere. Now I\nask what conceivable central function can be ascribed to a cell which\nterminates the fibre in a peripheral ganglion, or which is merely\nan enlargement in the course of a fibre in a nerve-bundle? Besides\nthe facts already adduced, let attention be called to this: If a\nnerve-bundle from the _submucosa_ of the intestine be examined, there\nappear among the fibres many nuclei (neuroblasts), and occasionally\ncells, unipolar and bipolar. These cells--if we may trust the\nobservations of Rouget on the earliest development of nerves, and of\nSigmund Mayer on regenerated nerves--are simply more advanced stages of\nevolution of the neuroblasts; but whatever their genesis may be, there\ncan be nothing in the nature of a central function assigned to them.\n\n154. It may be asked, What part can we assign to cells in neural\nactions if they are apolar, unipolar, and even when multipolar,\nisolated from each other, and from fibres? I confess that I have\nno answer ready, not even an hypothesis. Until some rational\ninterpretation of the cell be given we must be content to hold an\nanswer in suspense. What I would urge is that we are precipitate\nin assuming that the anatomical connection between one element and\nanother must necessarily be that of a fibre. In a semi-fluid substance,\nsuch as neurine, continuity may be perfect without solid fibres: the\namorphous substance and the plasmode may as well transmit waves of\nmolecular motion from one part of the tissue to another, and therefore\nfrom cell to cell, or from cell to fibre, as a figured substance\nmay. When the posterior root enters the gray substance of the cord,\nthere is no more necessity for its fibres passing directly into the\ncells of that gray substance, in order to excite their activity, than\nthere is for a wire to pass from the bell to the ear of the servant,\nwho hears the vibrations of the bell through the pulsations of the\nintervening air upon her tympanum. Look at the structure of the retina,\nor the cerebellum, and you will find that the ganglionic cells which\nhave processes passing in a direction contrary to that whence the\nstimulus arrives, have none where continuity of fibre and cell would\nbe indispensable on the current hypothesis. Light stimulates the\nrods and cones, but there are no nerve-fibres, hitherto discovered,\npassing from these to the ganglionic cells; instead of that there is\na ground-substance thickly interspersed with granules and nuclei.\n_From_ the cells we see processes issue; _to_ the cells none are seen\narriving. So with the cerebellum. The large cells send their processes\nupwards to the surface; but downwards towards the white substance the\nprocesses are lost in the granular layer, which most histologists\nregard as connective tissue.\n\n155. A mere glance at nervous tissue in any part will show that cells\nare far from forming the principal constituents. In the epidermis or\na gland the cell is obviously the chief element, forming the bulk of\nthe tissue, and being the characteristic agent. In nerve-tissue, as in\nconnective tissue, the reverse is the case. We must therefore cease to\nregard the cell as having the importance now attached to it, and must\nrather throw the emphasis on the fibres and neuroglia.\n\n156. Before quitting this subject let a word be said on the amazing\nclassification which has attained wide acceptance (although rejected by\nthe most eminent authorities), founded on the size of the cells--the\nlarge multipolar cells being specified as motor, the smaller cells as\nsensory, while those of an intermediate size are sympathetic. I forbear\nto dwell on the development of this notion which specifies sensational,\nideational, and emotional cells, because this does not pretend to have\na basis in observation; whereas there are anatomical facts which give\na certain superficial plausibility to the original classification.\nThe conception is profoundly unphysiological; yet, if the anatomical\nevidence were constant, one might give it another interpretation. The\nevidence is, however, not constant. Large cells are found in regions\nassigned to sensory nerves, and small cells in motor regions. In the\nspinal cord of the tortoise Stieda declares that the so-called motor\ncells are limited to the cervical and lumbar enlargements; all the rest\nof the motor region being absolutely destitute of them.[182] Again\nlook at the cells of the retina--no one will assign motor functions to\nthem--yet they are the same as those of the cerebellum and the anterior\nhorns of the spinal cord. (It is worth a passing mention that the\nstructure of the nervous parts of the retina more closely resembles\nthat of the cerebellum than of the cerebrum.)\n\n157. While our knowledge of the cell is thus far indeed from having\nthe precision which the text-books display, and in no sense warrants\nthe current physiological interpretations, our knowledge of fibres and\nneuroglia is also too incomplete for theoretic purposes. We know that\nthe axis cylinder is the essential element; but we are still at a loss\nwhat part is to be assigned to the medullary sheath. There is indeed a\npopular hypothesis which pronounces it to be the means of _insulating_\nthe fibre, and thus preserving the isolated conduction of nerve-force.\nBeing of a fatty nature, this insulating office was readily suggested\nin agreement with the assumption that Neurility was Electricity. Now,\nwithout discussing whether Neurility is or is not Electricity, even\nadmitting the former to be satisfactorily proved, I must remark that\nthe admission still leaves the medullary sheath incapable of fulfilling\nthe supposed office, since not only is there no such sheath in most of\nthe invertebrates and in the sympathetic nerves of vertebrates, but\neven in those nerves which have the sheath it is precisely in places\nwhere the insulation would be most needed--namely, just before the\nterminations of the fibres in muscles and in centres--that the sheath\nis _absent_. This is as if we tried to conduct water through a pipe\nwhich fell short at both ends--before it left the cistern, and before\nit reached the spot to be watered. If there is a tendency in Neurility\nto spread wherever it is not insulated by a medullary sheath, then\nbefore reaching the centres and the muscles, it must, on the insulating\nhypothesis, dribble away!\n\n158. The facts expressed in the \u201claw of isolated conduction\u201d are\nimportant, and are difficult of explanation; but it is obvious that\nthey cannot be referred to the presence of the medullary sheath. Nor\nindeed will any insight into the propagation of stimulation through\nthe central axis be intelligible until we have reformed our anatomical\ntheories, and taken the Neuroglia into account. The theory which\nconnects every fibre directly with a cell, and every cell with another\nby anastomosis--even were it demonstrated--would not explain the law\nof isolated conduction. Butzke cogently remarks[183] that such a\ndisposition of the elements should render all neural paths invariable;\nwhereas the fact is that they are very variable. We learn to perform\nactions, and then we unlearn them; the paths are traversed now in\none direction, now in another. Fluctuation is the characteristic\nof central combinations. And for this fluctuating combination of\nelements a corresponding diversity is required in the possible\nchannels. This seems to be furnished by the network of the Neuroglia.\nSee the representation copied from Butzke\u2019s plate, and note how the\ncell-process blends with the meshes of the Neuroglia. Is it fanciful\nto regard this network of fibrils as having somewhat the relation of\ncapillaries to blood-vessels? Did we not experimentally know that the\ncapillaries are terminal blood-vessels, we should not suspect it from\nmere examination of the structure.\n\n159. Having insisted that our knowledge is insufficient for any\nexplanation of the \u201claw of isolated conduction,\u201d I can only suggest a\npath of research which may lead to some result. What we know is that\nsome stimulations are propagated from one end of the cerebro-spinal\naxis to the other in definitely _restricted_ paths, while others are\n_irradiated_ along many paths. In the succeeding chapter this will be\nmore fully considered; what we have here to note is that the manifold\nirradiations of a stimulation have an anatomical substratum in the\nmanifold sub-divisions of the network of fibrils and the amorphous\nsubstance in which they penetrate.\n\n[Illustration: Fig.\u00a026.--_Nerve-cells with processes terminating in\nneuroglia._]\n\n160. In conclusion, I would say, let no one place a too great\nconfidence in the reigning doctrines respecting the elementary\nstructure of the nervous system, but accept every statement as a\n\u201cworking hypothesis\u201d which has its value in so far as it links together\nverified facts, or suggests new research, but is wholly without value\nin so far as it is made a basis of deductions not otherwise verified.\nHypotheses are indispensable to research, but they must be accompanied\nby vigilant scepticism. Imagination is only an enemy to Science when\nScepticism is asleep.\n\n\n\n\nCHAPTER VIII.\n\nTHE LAWS OF NERVOUS ACTIVITY.\n\n\n161. The foregoing remarks have had the object of showing how little\nsubstantial aid Psychology can at present derive from what is known\nof the elementary structure of the nervous system, indispensable\nas an accurate knowledge of that structure must be to a complete\nanalysis of its functions. This caution has been specially addressed\nto those medical and psychological students whose researches leave\nthem insufficient leisure to pursue microscopical investigations\nfor themselves, and who are therefore forced to rely on second-hand\nknowledge, which is usually defective in the many qualifying\nconsiderations which keep scepticism vigilant. Relying on positive\nstatements, and delusive diagrams which only display what the observer\n_imagines_, not what he actually _sees_, they construct on such data\ntheories of disease, or of mental processes; or else they translate\nobserved facts into the terms of this imaginary anatomy, and offer the\ntranslation as a new contribution to Science.\n\n162. But little aid as can at present be derived from the teaching of\nthe microscope, some aid Psychology may even now derive from it. The\nteaching will often serve, for instance, to correct the precipitate\nconclusions of subjective analysis, which present artificial\ndistinctions as real distinctions, separating what Nature has united.\nIt will show certain organic connections not previously suspected;\nand since whatever is organically connected cannot functionally be\nseparated, such sharply marked analytical distinctions as those of\nperiphery and centre, or of sensation and motion, must be only regarded\nas artificial aids. The demonstration of the indissoluble union of\nthe tissues is a demonstration of their functional co-operation. So\nalso the anatomical demonstration of the similarity and continuity of\nall parts of the central system sets aside the analytical separation\nof one centre from another, except as a convenient artifice; proving\nthat cerebral substance is one with spinal substance, having the same\nproperties, the same laws of action.\n\nFor the present, Psychology must seek objective aid from Physiology\nand Pathology rather than from elementary Anatomy. In the paragraphs\nwhich are to follow I shall endeavor to select the chief laws of\nnervous activity which the researches of physiologists and pathologists\ndisclose. By these laws we may direct and control psychological\nresearch.\n\n\nTHE ENERGY OF NEURILITY.\n\n163. Vitality is characterized by incessant molecular movement, both\nof composition and decomposition, in the building up of structure and\nthe liberation of energy. The life of every organism is a complex of\nchanges, each of which directly or indirectly affects the statical\nand dynamical relations, each being the resultant of many co-operant\nforces. In the nourishment of every organite there is an accumulation\nof molecular _tension_, that is to say, stored-up energy in a latent\nstate, ready to be expended in the activity of that organite; and this\nexpenditure may take place in a steady flow, or in a sudden gush.\nThe molecular movements under one aspect may be called convergent,\nor _formative_: they build the structure, and tend to the state of\nequilibrium which we call the statical condition of the organite,\ni.\u00a0e. the condition in which it is not active, but ready to act.\nPerfect equilibrium is of course never attained, owing to the\nincessant molecular change: indeed Life is inconsistent with complete\nrepose. Under another aspect the molecular movements may be called\n_discharging_: they constitute the dynamic condition of the organite,\nin which its functional activity appears. The energy is now diverted,\nliberated, and the surplus, over and above that which is absorbed in\nformation, instead of slowly dribbling off, gushes forth in a directed\nstream. The slow formation of a secretion in a gland-cell, and the\ndischarge of that secretion, will illustrate this; or (if muscular\n_tone_ be admitted) the incipient contraction of the chronic state, and\nthe complete contraction of the dynamic state, may also be cited.\n\n164. The discharge which follows excitation may thus be viewed as\na _directed quantity_ of molecular movement. Because it is always\nstrictly relative to the energy of tension, and is inevitable when\nthat tension attains a certain surplus over what is required in\nconstruction, there is a limit, 1\u00b0, to the growth and evolution of\nevery organite, and every organism (comp. Problem I. \u00a7 118), and, 2\u00b0,\nto its dynamical effect. When there is no surplus, the organite is\nincapable of discharge: it is then exhausted, i.\u00a0e. will not respond to\nstimulus.\n\n165. The speciality of nerve-tissue is its pre-eminence in directive\nenergy. Like all other tissues, it grows, develops, and dies; but\nabove all others it has what we call _excitability_, or readiness in\ndischarging its energy in a directed stream. By its topographical\ndistribution it plays the functional part of exciting the activity of\nother tissues: it transmits molecular disturbance from periphery to\ncentre, from centre to centre, and from centre to muscles, vessels, and\nglands. When a muscle is excited it moves, and when a gland is excited\nit secretes; but these actions end, so to speak, with themselves; the\nmuscle does not directly move any other muscle;[184] the gland does not\ndirectly excite any other gland. The nerve, on the contrary, has always\na wide-spreading effect; it excites a centre which is continuous with\nother centres; and in exciting one muscle, usually excites a group.\nHence the nervous system is that _which binds the different organs\ninto a dynamic unity_. And Comparative Anatomy teaches that there is a\nparallelism between the development of this system and the efficient\ncomplexity of the organism. As the tissues become more and more\nspecialized, and the organs more and more individualized, they would\nbecome more and more unsuited to the general service of the organism,\nwere it not that a corresponding development of the nervous system\nbrought a unifying mechanism.\n\nThe great instability of neurine, in other words, its high degree of\ntension, renders it especially apt to disturb the tension of other\ntissues. It is very variable; and this variability will have to be\ntaken into account in explaining the restriction of discharges to\nparticular centres. A good example of exaggerated tension is furnished\nby strychnine poisoning. The centres are then so readily excitable\nthat a touch, or a puff of cold air on the skin, will determine\nconvulsions. And it is worthy of remark that for some hours after this\nconvulsive discharge the centres return to something like their normal\nstate; and the animal may then be stroked, pinched, or blown upon\nwithout abnormal reactions. But during this interval the centres are\nslowly accumulating excess of tension from the poisoned blood; and at\nthe close, convulsions will again follow the slightest stimulus. This\nalternation of exhaustion and recrudescence is noticed by Schr\u00f6der\nvan der Kolk in the periodicity of the phenomena exhibited in spinal\ndisease.[185]\n\n\nTHE PROPAGATION OF EXCITATION.\n\n166. Understanding, then, that the propagation of an excitation\ndepends on the state of tension of the tissue, and always follows\nthe line of least resistance, whichever that may be at the moment,\nwe have to inquire whether the transmission takes place only in one\ndirection, from periphery to centre in sensory nerves, and from centre\nto periphery in motor nerves? By most physiologists this is answered\naffirmatively. Indeed a special property has been assigned to each\nnerve, in virtue of this imaginary limitation of centripetal and\ncentrifugal conduction. The \u201cnerve-current\u201d (accepted as a physical\nfact, and not simply a metaphor) is supposed to \u201cflow\u201d from the\ncentral cells along the motor nerve to the muscles; but by a strange\noversight the current is also made to \u201cflow\u201d _towards_ the central\ncells which are said to produce it! Now although the fact may be, and\nprobably is, that normally the sensory nerve, being stimulated at its\nperipheral end, propagates the stimulation towards the centre, and the\nmotor nerve propagates its central stimulation towards the periphery,\nthe question whether each nerve is not capable of transmission in\nboth directions is not thus answered. _A priori_ it is irrational to\nassert that nerves fundamentally alike in composition and structure\nare unlike in properties; and we might as well suppose that a train\nof gunpowder could only be fired at one end, as to suppose that a\nnerve could only be excited at one end. And how does the evidence\nsupport this _a priori_ conclusion? Dubois Reymond proved that each\nnerve conducted electricity in both directions; but as Neurility\nhas not been satisfactorily shown to be identical with the electric\ncurrent, this may not be considered decisive. Such a doubt does not\nhang over the following facts. M. Paul Bert, pursuing John Hunter\u2019s\ncurious experiments on animal _grafting_, has grafted the tail of\na rat under the skin of the rat\u2019s back, the tip of the tail being\ninserted under the skin, its base rising into the air, so that there\nis here an inversion of the normal position. In the course of time\nSensibility gradually reappears in this grafted tail; and at the\nend of about twelve months the rat not only feels when the tail is\npinched, but knows _where_ the irritation lies, and turns round to bite\nthe pincers.[186] Here we have a case of a sensory nerve reversed,\nyet transmitting stimulation from the base to the tip of the tail,\ninstead of from the tip to the base, as in a normal organ. Vulpian\nand Philippeaux having divided two nerves, united the central end of\nthe sensory nerve with the peripheral end of the motor nerve; when\nthe organic union was complete, and each nerve was formed out of the\nhalves of two different nerves, the effect of pinching one of these\nwas to produce simultaneously pain and movement, showing that the\nexcitation was transmitted upwards to the centre, and downwards to the\nmuscles.[187] It may be compared with a train of gunpowder having a\nloaded cannon at one end and a bundle of straw at the other, when if a\nspark be dropped anywhere on this train, the flame runs along in both\ndirections, explodes the cannon, and sets alight the straw.\n\n167. Indeed we have only to remember the semi-liquid nature of the\naxis cylinder to see at once that it must conduct a wave of motion as\nreadily in one direction as in another. A liquid transmits waves in any\ndirection according to the initial impulse. There is consequently no\nreason for asserting that because the usual direction is centripetal\nin a sensory nerve, and centrifugal in a motor nerve, each nerve is\n_incapable_ of transmitting excitations in both directions. And I think\nmany phenomena are more intelligible on the assumption that neural\ntransmission is in both directions. If the eye is fixed steadfastly\non a particular color during some minutes, the retina becomes\nexhausted, and no longer responds to the stimulus of that color: here\nthe stimulation is of course centripetal. But if instead of looking\nintently on the color, the mind (in complete absence of light) pictures\nit intently, _this cerebral image is equally capable of exhausting the\nretina_; and unless we believe that color is a cerebral, not a retinal\nphenomenon (which is my private opinion), we must accept this as proof\nof a centrifugal excitation of a sensory tract. Another illustration\nmay be drawn from the muscular sense. There may be a few sensory fibres\ndistributed to muscles; but even if the observations of Sachs[188]\nshould be confirmed, I do not think that all muscle sensations can be\nassigned to these fibres, but that the so-called motor fibres must\nalso co-operate. When a nerve acts upon a muscle, the muscle reacts\non the nerve; and when a nerve acts on a centre, the centre reacts on\nthe nerve. The agitation of the central tissue cannot leave the nerve\nwhich blends with it unaffected; the agitation of the muscular tissue\nmust also by a reversal of the \u201ccurrent\u201d affect its nerve. Laplace\npoints out how the movement of the hand which holds a suspended chain\nis propagated along the chain to its terminus, and if when the chain\nis at rest we once more set that terminus in motion, the vibration\nwill remount to the hand.[189] The contraction of a muscle will not\nonly stimulate the sensory fibres distributed through it, but also, I\nconceive, stimulate the very motor fibres which caused the contraction,\nsince these fibres blend with the muscle.[190]\n\n168. To understand this, it is necessary to remember that the\nstimulation of a nerve does not arise[191] in the _changed state_ of\nthat nerve, but in the _process of change_, i.\u00a0e. the disturbance of\nthe tension. The duration of the stimulation is that of the changing\nprocess, and the intensity increases with the differential of the\nvelocity of change. So that when a nerve which has been excited by a\nchange of state returns to its former state, this return--being another\nchange--is a new excitation. That it is not the changed state, but the\nchange, which is operative, explains the fact noted by Brown S\u00e9quard:\na frog poisoned by strychnine, when decapitated and all respiration\ndestroyed, will remain motionless for days together, if carefully\nprotected from all external excitation; but its nervous system is in\nsuch a state of tension all this time that the first touch produces\ngeneral convulsions. Freusberg also notes that if a brainless frog be\nsuspended by the lower jaw, and one foot be pinched, the other leg is\nmoved at first, then quickly droops again, and remains at rest until\nthe pincers are removed from the pinched foot, when suddenly all four\nlegs are violently moved by the _stimulation which the simple removal\nproduces_. Let us also add the well-known and significant fact that\nif a nerve be divided rapidly by a sharp razor, neither sensation\nnor motion is produced, because the intensity of a stimulus being,\nto speak mathematically, _the function of the changing process_, the\nduration of the process is in this case too brief. On the same ground\nthe application of a stimulus will excite no movement, if the force be\nvery slowly increased from zero to an intensity which will destroy the\nnerve; but at any stage a _sudden_ increase will excite a movement.\n\n169. We may group all the foregoing considerations in this formula:\n\n  LAW I. Every neural process is due to a sudden disturbance of the\n      molecular tension. The liberated energy is discharged along the\n      lines of least resistance.\n\nThe conditions which determine the lines of least resistance are\nmanifold and variable. The nervous system is a continuous whole, each\npart of which is connected with diverse organs; but in spite of this\nanatomical diversity, the deeper uniformity causes the activity of\neach part to depend on and involve the activity of every other, more\nor less. By \u201cmore or less\u201d is meant, that although the excitation of\none part necessarily affects the state of all the others, because of\ntheir structural community, so that _each sensation and each motion\nreally represents a change in the whole organism_, yet the responsive\ndischarge determined in each organ by this change, depends on the\ntension of the organ and its centre at that moment. A bad harvest\nreally affects the whole nation; but its effect is conspicuous on the\nwelfare of the poor rather than of the rich, although the price of\nbread is the same to rich and poor. Nervous centres, and muscular or\nglandular organs, differ in their excitability; one condition of this\ngreater excitability being the greater frequency with which they are\ncalled into activity. The medulla oblongata is normally more excitable\nthan the medulla spinalis; the heart more than the limbs. Hence a\nstimulus which will increase the respiration and the pulse may have no\n_appreciable_ effect on the limbs; but some effect it must have.\n\n170. Imagine all the nerve-centres to be a connected group of bells\nvarying in size. Every agitation of the connecting wire will more or\nless agitate all the bells; but since some are heavier than others,\nand some of the cranks less movable, there will be many vibrations\nof the wire which will cause some bells to sound, others simply to\noscillate without sounding, and others not sensibly to oscillate.\nEven some of the lighter bells will not ring if any external pressure\narrests them; or if they are already ringing, the added impulses, not\nbeing rhythmically timed, will _arrest_ the ringing. So the stimulus\nof a sensory nerve agitates its centre, and through it the whole\nsystem; usually the stimulation is mainly reflected on the group of\nmuscles innervated from that centre, because this is the readiest path\nof discharge; but it sometimes does not mainly discharge along this\npath, the line of least resistance lying in another direction; and the\ndischarge never takes this path without also irradiating upwards and\ndownwards through the central tissue. Thus irradiated, it falls into\nthe general stream of neural processes; and according to the state in\nwhich the various centres are at the moment it modifies their activity.\nA nervous shock--physical or mental--sensibly affects all the organs. A\nsevere wound paralyzes, for a time, parts far removed from the wounded\nspot. A blow on the stomach will arrest the heart; a fright will do\nthe same. Terror relaxes the limbs, or sets them trembling; so does\na concussion: if a frog be thrown violently on the ground, all its\nmuscles are convulsed; but if the nerves of one limb be divided before\nthe shock, the muscles of that limb will not be convulsed.\n\n171. We are apt to regard the discharge on the moving organs as if\nthat were the sole response of a stimulation; but although the most\nconspicuous, it is by no means the most important effect. Besides\nexciting the muscles, more or less, every neural process has its\ninfluence on the organic processes of secretion, and effects thermal\nand electrical changes. Schiff has demonstrated that every sensation\nraises the temperature of the brain; Nothnagel, that irritation of a\nsensory nerve causes constriction of the cerebral arteries, and hence\ncerebral an\u00e6mia. Brown S\u00e9quard and Lombard find the temperature of\na limb raised when its skin is pinched, and lowered when the skin\n_elsewhere_ is pinched. Georges Pouchet has shown that fishes change\ncolor according to the brightness or darkness of the ground over which\nthey remain; and these changes are dependent on nervous stimulation,\nmainly through the eye, division of the optic nerves preventing the\nchange. These are so many _a posteriori_ confirmations of what _a\npriori_ may be foreseen. They are cited here merely to enforce the\nconsideration, seldom adequately kept before the mind, that every\nneural process is a change which causes other changes in the whole\norganism.\n\n\nSTIMULI.\n\n172. Stimuli are classed as external and internal, or physical and\nphysiological. The one class comprises all the agencies in the\nExternal Medium which _appreciably_ affect the organism; the other\nclass all the changes _in_ the organism which appreciably disturb the\nequilibrium of any organ. Although the pressure of the atmosphere, for\nexample, unquestionably affects the organism, and determines organic\nprocesses, it is not reckoned as a stimulus unless the effect become\nappreciable under sudden variations of the pressure. In like manner\nthe blood is not reckoned among the internal stimuli, except when\nsudden variations in its composition, or its circulation, determine\nappreciable changes. Because the external stimuli, and the so-called\nSenses which respond to them, are more conspicuous than the internal\nstimuli and the Systemic Senses, they have unfortunately usurped too\nmuch attention. The massive influence of the Systemic Sensations in\ndetermining the desires, volitions, and conceptions of mankind has not\nbeen adequately recognized. Yet every one knows the effect of impure\nair, or a congested liver, in swaying the mental mood; and how a\nheavy meal interferes with muscular and mental exertion.[192] What is\nconspicuous in such marked effects, is less conspicuously, but not less\nnecessarily, present in slighter stimuli.\n\n173. A constant pressure on the tympanum excites no sound; only a\nrhythmic alternation of pressures will excite the sensation. A constant\ntemperature is not felt; only changes in temperature. If Light and\nSound were as uniform as the circulation of the blood, or the pressure\nof the atmosphere, we should be seldom conscious of the existence of\nthese stimuli. But because the changes are varied and marked, our\nattention is necessarily arrested by them. The changes going on within\nthe tissues are too graduated to fix the attention; it is only by\nconsidering their cumulative effects that we become impressed with\ntheir importance. For example, the development of the sexual glands\ndetermines conspicuous physical and moral results--we note consequent\neffects on voice, hair, horns, structure of the skull and size of the\nmuscles, no less than the rise of new feelings, desires, instincts,\nideas. Any organic interference with the activity of the ovaries will\nalter the moral disposition of the animal: suppression of this organic\nprocess means non-development of the feelings of maternity; the moral\nsuperstructure is absent because its physical basis is wanting.\n\n174. Blood supplies the tissues with their plasmodes; a constant\nsupply of oxygenated blood is therefore necessary to the vitality of\nthe tissues. But it is an error to suppose that oxygen is the special\nstimulus of nerve-centres, or that their activity depends on their\noxidation; on the contrary, the deficiency of oxygen or surplus of\ncarbonic acid is that which stimulates. When saturated with oxygen,\nthe blood paralyzes respiration; when some of the oxygen is withdrawn,\nrespiration revives. Here--as in all other cases--we have to remember\nthat differences in degree readily pass into differences in kind,\nso that an excess of a stimulus produces a reversal of the effect;\nthus although surplus of carbonic acid excites respiratory movements,\nexcess of carbonic acid causes Asphyxia. Abundance of blood is\nrequisite for the continuous activity of nerve-centres; but while a\ntemporary deficiency of blood renders them more excitable, too great a\ndeficiency paralyzes them. An\u00e6mia, which causes great excitability, and\nconvulsions (so that nerves when dying are most irritable), may easily\nbecome the cause of the death of the tissue. There are substances which\ncan only be dissolved by a given quantity of liquid; if this quantity\nbe in excess, they are precipitated from the solution. There are\nvibrations of a given order which cause each string to respond; change\nthe special order, and the string returns to its repose.\n\nIn the stillness and darkness of the night we are excluded from most\nof the external stimuli, yet a massive stream of systemic sensations\nkeeps the sensitive mechanism active, and in sleep directs the dreams.\nThe cramps and epileptiform attacks which occur during sleep are most\nprobably due to the over-excitability produced by surplus carbonic\nacid. To temporary an\u00e6mia may be assigned the strange exaggeration of\nour sensations during the moments which precede awakening; and the\ngreater vividness of dream-images.\n\nIt is only needful to mention in passing the varied stimuli by which\ncerebral changes act upon the organism. The mention of a name will\ncause a blush, a brightening of the eye, a quickening of the pulse. The\nthought of her absent infant will cause a flow of milk in the mother\u2019s\nbreast.\n\n175. We may formulate the foregoing considerations in another law:\n\n  LAW II. The neural excitation, which is itself a change, directly\n      causes a change in the organ innervated, and indirectly in the\n      whole organism.\n\nThe significance of this law is, that although for the convenience\nof research and exposition we isolate one organ from the rest of the\norganism, and one process from all the co-operant processes, we have to\nremember that this is an artifice, and that in reality there is no such\nseparation.\n\n\nSTIMULATION.\n\n176. Passing now from these general considerations to their special\napplication, we may formulate the law of stimulation:\n\n  LAW III. A faint or moderate stimulation increases the activity\n      of the organ; but beyond a certain limit, increase of\n      stimulation diminishes, and finally arrests, the activity.\n      Duration of stimulation is equivalent to increase.\n\nA muscle stimulated contracts; if the stimulation be repeated,\nthe muscle becomes tetanized, and in this state has reached its\nlimit; a fresh stimulation then _relaxes_ the muscle. A very faint\nstimulation of the vagus quickens the pulsation of the heart, but a\nslight increase, or duration of the stimulation, slackens and arrests\nthe heart.[193] Every one knows how a moderate feeling of surprise,\npleasure, or pain quickens the heart and the respiration; and how a\nshock of surprise, joy, grief, or great physical pain depresses,\nand even arrests them. Excess of light is blinding; excess of sound\ndeafening.\n\n177. The nervous system is incessantly stimulated, and variably.\nHence a great variation in the excitability of different parts. While\nthe regular and moderate activity of one part is accompanied by a\nregular flow of blood to it, so that there is a tolerably constant\nrhythm of nutrition and discharge, any irregular or excessive activity\nexhausts it, until there has been a nutritive restoration. We can\nthus understand how one centre may be temporarily exhausted while\na neighboring centre is vigorous. Cayrade decapitated a frog, and\nsuspended light weights to each of its hind legs; when either leg was\nstimulated, the weight attached to it was raised. After each repetition\nthe weight was raised less and less, until finally the weight ceased to\nbe raised: the centre had been exhausted. But now when the other leg,\nwhich had been in repose, was stimulated, it energetically contracted,\nand raised its attached weight; showing that its centre was not\nexhausted by the action of the other.[194]\n\n178. This seems in contradiction with the principle that the excitation\nof one centre is an excitation of all. It also seems in contradiction\nwith the principle urged by Herzen, that irritation of one sciatic\nnerve _diminishes_ the excitability of the opposite leg; and this again\nseems contradicted by the principle urged by Setschenow, that although\nmoderate excitation of one sciatic nerve will diminish the excitability\nof the other, a powerful excitation will increase it.\n\n179. All three principles are, I believe, exact expressions of\nexperimental evidence; and their seeming contradictions may be\nreconciled on a wider survey of the laws of neural activity,\ninterpreted according to the special conditions of each case. These\nlaws may be conveniently classified as laws of Discharge, and Laws of\nArrest; the second being only a particular aspect of the first.\n\n\nTHE LAW OF DISCHARGE.\n\n180. The physiological independence of organs, together with their\nintimate dependence in the organism, and the fact that this organism is\nincessantly stimulated from many sides at once, assure us _a priori_\nthat the \u201cwaves\u201d of molecular movement due to each stimulus must\nsometimes interfere and sometimes blend with others, thus diverting or\nneutralizing the final discharge in the one case, and in the other case\nswelling the current and increasing the energy of the discharge. We\nare accustomed to speak of one part \u201cplaying on another,\u201d sympathizing\nwith another, and so on; but what is the process expressed in these\nmetaphors? When an idea, or a painful sensation, quickens the pulse,\nor increases the flow of a secretion, we are not to imagine that from\na spot in the cerebrum, or the surface, there is a nerve-fibre going\ndirectly to the heart, or the gland, transmitting an impulse; in each\ncase the central tissue has been agitated by a sudden change at the\nstimulated point, and the discharge on heart and gland is the resultant\nof this agitation along the lines of least resistance. The nerves of\nthe great toe, for example, pass into the spinal cord at a considerable\ndistance from the spot where the nerves of the arm enter it; when,\ntherefore, the great toe is pinched, the arm does not move by direct\nstimulation of its nerves, but by the indirect stimulation which has\ntraversed the whole central substance.\n\n181. This is intelligible when we know that the whole central substance\nis continuous throughout; but the difficulty arises when we have to\nexplain why, if this central substance is stimulated throughout,\n_only_ arms and legs respond; in other words, why the toe-centre\n\u201cplays upon\u201d the arm-centre, and not on the others? When a frog is\ndecapitated, if we gently touch one leg with the point of the scalpel,\nthe leg will move, but only this leg. Prick more forcibly, and both\nlegs will move. Keep on pricking, and all four legs are drawn up, and\nthe frog hops away. Each excitation was propagated along the cord;\nbut the discharge was restricted in the first case to one limb, in\nthe second to two, in the third it involved all the muscles of the\ntrunk. At the sight of a friend a dog wags his tail gently: as there\nis no _direct_ connection between the optic nerves and the tail, this\nplaying of one centre on another must be by the agency of intermediate\ncentres; and we know that if the dog\u2019s spinal cord be divided, this\nexcitation from the optic centre is no longer possible, yet the tail\nwill wag if the abdomen be tickled, or the leg pinched. Now compare the\neffect on the dog produced by the sight of his master, or of a friend\naccustomed to take him out. There is no longer a gentle wagging of the\ntail, but an agitation of the whole body: he barks, leaps, and runs\nabout; the central stimulation is discharged through many outlets; and\ncould we test the effect, we should find an appreciable alteration\nin the thermal and electrical condition of the whole organism, with\ncorresponding changes in circulation, secretion, etc. So different are\nthe consequences of two slightly different retinal impressions mingling\ntheir stimulations with the same mass of central substance!\n\n182. The discharge is determined by two conditions: the state of\ntension, and the energy of the stimulation. _The state of tension is\nincreased by every stimulation which falls short of a discharge_; that\nis to say, faint and frequent stimulation augments the excitability,\nwhereas powerful stimulation exhausts it. When, therefore, one\nwave succeeds another in the same direction, it reaches a centre\nmore disposed to discharge; or, as Cayrade expresses it, \u201ca certain\nagitation of the cells is necessary for the manifestation of their\nproperty of reaction, in the same way that the concentric circles\nproduced on the surface of water by a falling stone are more rapid and\nmore numerous if a stone has already agitated the surface.\u201d\n\n183. So much for the tension. What has been called the energy of the\nstimulation is more complicated. It is not measurable as a simple\nphysical process; we cannot say that a given quantity of any external\nforce will determine a given discharge. It is mostly complicated by\npsychical processes, and these so modify the result that instead of the\npredicted discharge there is arrest, or discharge from another centre.\nPress a dog\u2019s skin with increasing violence, and the effect increases\nfrom pleasurable to painful irritation; but whether the dog will cry\nout and bite, or cry out and struggle to escape, depends upon whether\nthe pincher is a stranger or a friend. If you hurt a dog while removing\na thorn from its foot it will cry out, but although the pain causes it\nto initiate a biting movement, by the time your hand is reached that\nmovement will have been changed, and the dog will lick the hand which\nhe knows is hurting him in the endeavor to relieve him of the thorn.\nThe co-operation of the mind is here evident enough. A purely psychical\nprocess has interfered with the purely physiological process. And I\nshall hereafter endeavor to show that psychical processes analogous in\nkind though simpler in degree are really co-operant in actions of the\nspinal cord. The dog would be said to discriminate between the pain\ninflicted by a friend, and the same pain inflicted by a stranger. In\nother words, the sensitive mechanism would be differently determined\nin the direction of discharge, although the initial stimulation was the\nsame in each case. If we admit that the resulting action is in each\ncase the consequence of the particular group of elements co-operating,\nthere will be no ground for denying that analogous _discrimination_\nis manifested by the brainless animal, who also responds differently\nto different external stimuli, and differently to the same stimulus\nunder different central conditions. The brainless frog croaks if its\nback be gently stroked with the handle of a scalpel; but if the point\nbe used, or if the handle be roughly pressed, instead of croaking,\nthe frog raises his leg in defence. Here the difference in the\nperipheral irritation has excited a different reaction in the centre;\nand this might be interpreted as purely physical; if now the leg be\nfastened, and the movement of defence be thus prevented, the frog will\nemploy the other leg; or adopt some other means of relieving itself\nfrom the irritation. It was a mass of registered experiences which\ndetermined the dog not to bite his master. An analogous registration\nof experiences determines the changed reactions of the brainless frog.\nBut this is a point which can only be touched on in passing here, and\nit is touched on merely to facilitate our exposition of the complicated\nconditions of neural discharge. These may be formulated in\n\n  184. LAW IV. The simultaneous influence of several stimuli, each\n      of which separately excites the same centre, is cumulative:\n      stimuli then assist each other, and their resultant is their\n      _arithmetical_ sum.\n\n    Simultaneous stimuli, each of which excites a different centre,\n      _interfere_ with each other\u2019s energy, and their resultant is\n      their _algebraical_ sum.\n\nIn this law there is a condensed expression of that composition of\nforces which may either result in Discharge or Arrest. By simultaneity\nis not to be understood merely the coincidence of impressions, but also\nthe reverberations of impressions not yet neutralized by others. Thus\nwhen Sensibility is tested by the now common method,[195] it is found\nthat if one leg is withdrawn after a lapse of, say, ten pendulum beats,\nthe other leg, which has not been irritated, will nevertheless, on\nirritation, be withdrawn in less than ten beats, provided the central\nagitation caused by the first stimulation has _not yet subsided_. But,\non the contrary, the withdrawal will be considerably deferred, or\neven prevented altogether, if at the same time that the leg is acted\non by the acid, a more powerful excitation takes place in some other\npart of the body. In the one experiment we see simultaneous excitation\nin the same centre and the same direction. In the other simultaneous\nexcitation in different centres. The more powerful excitation\nsuppresses the discharge from the less powerful; but although it\nprevails, it loses just as much force as it arrests.[196]\n\n185. There is another very interesting experiment by Freusberg, which\nmust be cited here.[197] When the sciatic nerve is divided, the frog\u2019s\nleg is of course not withdrawn from the acidulated water, because in\nthat case no sensory excitation is propagated from the skin to the\ncentre; but although there is no stimulation from the skin, there is\none from the muscles, as appears in the fact that if a small weight be\nsuspended on this leg, the other leg is more rapidly withdrawn from the\nacidulated water--the action of the muscles having affected the centre\nand increased its excitability.\n\n186. When the motor group of one leg is moderately stimulated, the\ndischarge is confined to the muscles of that one leg; and according\nto Herzen the excitability of the motor group of the other leg is\nthereby somewhat diminished. But if the stimulation be increased, there\nis an irradiation to the other group, which irradiation, although\nnot sufficient to excite a discharge, renders it much more _ready_\nto discharge, so that a feeble stimulus suffices. This accords with\nSetschenow\u2019s observations, and is confirmed by Freusberg\u2019s experiment,\nin which, when one leg was stimulated by acid, if the acid were not\nwiped off but allowed to keep up the irritation, the other leg moved\nwithout being irritated; and this other leg having come to rest, when\nin its turn dipped in the acid, was more rapidly withdrawn than the\nfirst leg had been on first being stimulated; showing that the central\ngroups had become more excitable by the stimulation of either leg.\n\n187. While it is intelligible that an excitation of one group should\nincrease the activity of neighboring groups, by an increase of the\nvascular activity of the region, it is not so readily intelligible why\nthe feebler excitation of one group should diminish the excitability of\nits neighbor; yet the facts seem to warrant both statements.\n\n188. The conditions which determine Discharge are obscure. We may,\nhowever, say that anatomical and physiological data force the\nconclusion that whenever the central tissue is powerfully stimulated\nin any one part, there is either a discharge, or a greater tension\n(tendency to discharge) in every other part; in consequence of\nwhich, every fresh stimulus in the _same_ direction finds the parts\nmore prepared to react; while every fresh stimulus in a _contrary_\ndirection meets with a proportional resistance. Stated thus generally,\nthe principle is clear enough; but the immense complication of\nstimulations, and the statical variableness of the organs, renders its\napplication to particular cases extremely obscure. Why does the ticking\nof a clock arrest the attention, even with unpleasant obtrusiveness, at\none time, and presently afterwards cease to be heard at all? Why does\nthe cut of a knife cause intense pain, and a far greater cut received\nduring the heat and agitation of a quarrel pass unfelt? Why will the\nsame external force excite convulsions in all the muscles, and at\nanother time scarcely be distinguishable? These are consequences of the\ntemporary condition of the centres; but there are permanent conditions\nwhich in some organisms determine equally variable results. Thus the\nshock of terror which will simply agitate one person, will develop an\nepileptic attack in another, and insanity in a third; just as exposure\nto cold will in one person congest the liver, in another the lungs. A\nloud and sudden sound causes winking in most persons, and in many a\nsort of convulsive shock. The harsh noise of a file causes a shiver in\nsome persons, and in others \u201csets the teeth on edge,\u201d while in others\nit causes an increased flow of saliva.\n\n189. Nerves and centres have different degrees of excitability. The\nnerve-terminals in the skin are more sensitive to impressions than\nthose in the mucous membrane; those in the alimentary canal are more\nsensitive than those in the peritoneum; and all nerve-terminals are\nmore sensitive than nerve-trunks. A touch on the surface of the larynx\nwill produce a cough, but the nerve-trunk itself may be pinched or\ngalvanized without producing any such reflex. Moreover, there is the\ndifference of grouping. If the skin of the abdomen be tickled, there\nis a reflex on the adductor and extensor muscles of the leg; but these\nmovements are reversed if the skin of the back be tickled. Nor indeed\nare these movements invariable in either case; the one series will\nsometimes quite suddenly change to the other, if the irritation is kept\nup. That one and the same stimulus applied to the same spot should now\nexcite this group and now the other, shows that _both_ motor groups\nare affected, and that the discharge takes place from the one which at\nthe time being is in the highest tension. The alternation of tension\nexplains rhythmical discharge.\n\n\nTHE LAW OF ARREST.\n\n190. The Law of Arrest is only another aspect of the Law of Discharge,\nand may be regarded as the conflict of excitations. If a stranger\nenters the room where a woman lies in labor, there will often be caused\na sudden cessation of the uterine contractions.[198] Again, every one\nknows how the breathing and the beating of the heart are arrested by\nthe idea of danger. The arrest is in each of the three cases only\ntemporary, because when the shock of the new stimulus has caused its\ndischarge (arrest), the peripheral irritation which caused the former\ndischarges resumes its influence, and uterus, heart, and diaphragm\nbegin to move again, even more energetically. Note, moreover, that not\nonly will the cerebral excitation arrest the spinal discharge--an idea\ncheck the contractions of the uterus or the heart--but the reverse\nalso takes place. The brain of the woman may be intently occupied with\nsome scheme for the education or welfare of her expected child, but no\nsooner do the labor pains set in, than all these cerebral combinations\nare arrested.\n\n191. One sensation arrests another; one idea displaces another. If\nthe foreleg of a headless frog be irritated, the hind-leg will also\nbe moved by the stimulation; or _vice versa_. Here there has been a\npropagation of the excitation in either direction. But if while the\nlegs are thus irritated, and the centres are ready to discharge,\nanother and more powerful irritation reach the centre--say by pinching\nthe skin of the back--there will be no discharge on the legs. If the\nvagus be irritated, the heart is arrested; but this does not take place\nif at the same time, or immediately before, the foot has been sharply\npinched. A few gentle taps on the abdomen suffice to stop the heart;\nbut if a drop of acid be previously placed on the skin, we tap in vain,\nthe heart continues to beat. Brown S\u00e9quard cites several cases in which\nconvulsions were arrested by irritation of sensitive surfaces;[199]\nand Dr. Crichton Browne records a case of a patient in whom there was\nabolition of spinal reflex, due to cerebral irritation: tickling the\nsoles of the feet, or pricking the toes, which normally excites reflex\nmovements, in this case excited none whatever. \u201cThis seems to prove\nthat nerve currents, set in motion by irritation of the brain, or some\nof its convolutions, transmitted down the cord, may inhibit reflex\naction.\u201d[200] Examples might indefinitely be multiplied. Pinch the\nskin of a rabbit between the eyes, and you will observe that pulse and\nrespiration are slackened; but if the tail, which is very sensitive,\nbe pinched, this slackening is only momentary, and is succeeded by a\nquickening--unless the pain be great. Even the effect of intense pain\nmay be neutralized by stimulating the vagus--just as the effect of\nstimulating the vagus may be neutralized by pain. Claude Bernard found\nthat having dropped ammonia on the eyelid of a dog, the pain caused a\nconvulsive closure of the lid; but on galvanizing the vagus, the lid\nopened again, to be closed when the galvanism ceased.[201] When the\nheart is beating faintly (as in syncope), any irritating vapor applied\nto the nostrils will cause a more energetic pulsation; yet a very\nirritating vapor lowers the action of the heart beating normally, and\nwill even arrest that of a rabbit. Over-stimulation has almost always\nthe opposite effect of moderate stimulation.\n\n192. While there seems every reason to believe that an excitation\nnecessarily affects the whole cerebro-spinal axis, there is no doubt\nthat there is a certain restriction of this irradiation to definite\npaths, i.\u00a0e. the responsive discharge is confined to definite groups.\nSome of these restrictions are connate pathways: we bring them with us\nat birth; but most of them are pathways acquired after birth. The boy\nwho sheds tears at parting from his mother when he goes to school, will\nshed no tears when he parts from her to go to college, nay, perhaps\nwill shed none when he parts from her forever: not that his love has\nlessened, but that the idea of such expression of it as \u201cunmanly\u201d has\nbecome an organized tendency and arrests the tears. A youth of southern\nrace, who has not learned to be ashamed of tears, weeps freely under\nsuch circumstances.\n\n193. The pathways organized at birth are not many. Examples are the\ninspiration which follows expiration; the movements of coughing when\nthe larynx is tickled; the movements of swallowing, sneezing, etc. Even\nthese may be arrested for a brief time by what is called \u201cthe will\u201d;\nbut when once the discharge begins in any part of the mechanism, the\nwhole group is necessarily involved and the action is then inevitable.\nMany of the reflex actions which are universal are nevertheless\nacquired. Winking, for instance, when an object approaches the eye, is\nuniversal among us, but is never seen in infants, nor in animals. It\nis even doubtful whether the drawing up of the leg when the toes are\npinched is not an acquired reflex. Doubtful, I mean, in this sense,\nthat although the fact of non-withdrawal is observable in infants, who\ncannot localize their sensations, this may be due to the imperfect\ndevelopment of their nervous system. Mr. Spalding has proved that\nalthough the callow bird cannot fly, the mechanism of flight is no\nsooner developed than the action follows at once, without any previous\ntentative experiences.\n\n194. By experience we learn to restrict the paths of irradiation,\nso as to wink with one eye while the other is unmoved, to bend one\nfinger while the rest are extended, to move one limb, or one group of\nmuscles, while the others are at rest; in short, to execute any one\nparticular action, and not at the same time agitate superfluously many\nother organs. The boy when first learning to write is unable to prevent\nthe simultaneous motions of tongue and legs, which are ludicrously\nirrelevant to the purpose of writing; but he learns to keep all his\norgans in subjection, and only the eyes and hands active.[202] An\nanalogous restriction takes place in thinking. A train of thought is\nkept up by the exclusion of all suggestions which are not pertinent;\nand the power of the thinker is precisely this power of concentration.\n\n\nTHE HYPOTHESIS OF INHIBITORY CENTRES.\n\n195. The facts and their formulated laws which have just been adduced\nfurnish a sufficient explanation of all the phenomena of arrest\nwhich of late years have been detached and assigned to a special\nmechanism of inhibitory nerves and centres. In spite of the eminent\nauthorities countenancing the hypothesis of a particular set of\ninhibitory nerves, and particular centres of inhibition, I must confess\nthat the hypothesis appears to me inadmissible; and that I side with\nthose physiologists who hold that each nerve and each centre has its\ninhibitory action. Indeed, if the action of arrest be, as I maintain,\nonly another aspect of the action of discharge, the result of the\nconflict of forces, to say that all centres have the property of\nexcitation, is to say that all have the properties of discharge and\narrest: the discharge is only the resultant of the conflict along the\nline of least resistance; the arrest is the effect of the conflict\nalong the line of greatest resistance. The observed phenomena of\narrest are so varied and numerous that the upholders of the inhibitory\nhypothesis have been forced to invent not only arresting centres,\nbut centres which arrest these arresting centres! Dr. Lauder Brunton\ncandidly remarks: \u201cAt present our notions of nervous action seem to be\ngetting as involved as the Ptolemaic system of astronomy, and just as\nepicycles became heaped upon cycles, so nerve-centres are being added\nto nerve-centres. And yet, clumsy though the system may be, it serves\nat present a useful purpose, and may give real aid until a better\nis discovered.\u201d I do not think a Copernicus is needed to discover\na better. The Law of Arrest as a general neural law suffices, when\nthe right conception of a _centre_ as a physiological rather than an\nanatomical designation is admitted. (See p. 173.)\n\n196. It would be out of place here to consider the conflicting evidence\nwhich at present renders the question of the movements of the heart\none of the most unsatisfactory in the whole range of experimental\nphysiology. After devoting much time to it, and after writing a long\nchapter on it, I suppress what I had written, and content myself with\nthe statement that no advantage whatever is derived from the hypothesis\nof a special mechanism of arrest, unless perhaps in giving a temporary\nprecision to the direction of research. I mean that the search for\nspecial centres may lead to the discovery of the particular paths to\nwhich an impulse is restricted in any one action: as, for instance,\nthe vagus in retarding the pulsation of the heart. If the cerebrum can\ndetermine a movement, and combine various movements, it is a centre of\narrest; if the cerebellum can determine and regulate movements, it is a\ncentre of arrest; if the medulla oblongata can determine and regulate\nmovements, it is a centre of arrest; if the medulla spinalis can\ndetermine and combine movements, it is a centre of arrest; if a nerve\ncan dilate a constricted blood-vessel, or constrict a dilated one, it\nis a nerve of arrest. In other words, every centre exerts its action\neither in discharging, or in arresting the discharge of some other\ncentre.\n\nThe physiological process of Arrest may be physically interpreted\nas Interference;[203] not that the process in nerve-tissue is to be\nunderstood as the _same_ as that observed in fluids, or that the\nmetaphor of neural waves is to be taken for more than an intelligible\npicturing of the process; the difference in the two agents forbids our\nadmitting the resemblance to be more than analogical. Thus interpreted,\nhowever, we see that not only will one centre arrest the action of\nanother, but one nerve may be made to arrest itself! I mean that, under\nsimilar conditions of interference, the stimulation which normally\nfollows on external stimulus may be inhibited by a previous, or a\ncounter stimulation. Thus the nerve which will be stimulated by a\nchemical or mechanical stimulus, wholly fails to react if a constant\ncurrent is passing through it, although this constant current does not\nitself cause a constant contraction. Remove the electrodes, and then\nthe chemical or mechanical stimulus takes effect. Or the experiment\nmay be reversed: let the nerve be placed in a saline solution, and\nthe muscles will be at once thrown into violent contraction; if the\nelectrodes are now applied to the nerve, the contractions suddenly\ncease, to begin again directly the electrodes are removed.\n\n\nANATOMICAL INTERPRETATION OF THE LAWS.\n\n197. The problem for the anatomist is twofold: First, given the\norgan, he has to determine its function, or _vice versa_, given the\npart of an organ, to determine its functional relation; secondly,\ngiven the function, he has to determine its organ. The structural\nand functional relations of nerves and centres have been ascertained\nin a general way; we are quite sure that the posterior nerves carry\nexcitations from sensitive surfaces, that the anterior nerves carry\nexcitations to muscles and glands; and that the central gray substance\nnot only reflects a sensory excitation as a motor excitation, but\npropagates an excitation along the whole cerebro-spinal axis. But when\nwe come to a more minute analysis of the functional activities, and\nendeavor to assign their respective values to each part of the organic\nmechanism, the excessive complexity and delicacy of the mechanism\nbaffles research. We are forced to grope our way; and the light of the\nhypothetic lamps which we hold aloft as often misdirects as helps us.\nThe imaginary anatomy which at present gains acceptance, no doubt seems\nto simplify explanations; but this seeming turns out to be illusory\nwhen closely examined. The imagined arrangement of fibres and cells\nwe have seen to be not in agreement with observation; and were it\ndemonstrable, it would not account for the laws of propagation. Suppose\nsensory fibres to terminate in cells, and fibres from these to pass\n_upwards_ to other sensory cells and _transversely_ to motor cells, how\nin such a connected system could irradiations take place, if the law of\nisolated conduction were true? And how could isolated conduction take\nplace, if the excitation of a part were necessarily the excitation of\nthe whole? Why, for example, is pain not always irradiated? Why is it\neven localized in particular spots, determining movements in particular\nmuscles; and when irradiation takes place, why is it circumscribed,\nor--and this is very noteworthy--manifested in two widely different\nplaces, the intercostal and trigeminal nerves? Why does the irritation\nof intestinal worms manifest itself now by troubles of vision, now by\nnoises in the ear, and now by convulsions?\n\n198. Answers to such questions must be sought elsewhere. Our first\nsearch should be directed to the anatomical data, which have hitherto\nbeen so imprudently disregarded. Under the guidance of the laws\nformulated in this chapter, let us accept the anatomical fact of a\nvast network forming the ground-substance in which cells and fibres\nare embedded, and with which they are continuous; let us accept the\nphysiological principle Of similarity of property with similarity\nof composition and structure; let us accept the hypothesis that the\ndischarge of neural energy is dependent on the degree of stimulus\nand the degree of tension at the time being--and we shall have at\nleast a general theory of the process, though there will still remain\ngreat obscurities in particular applications. We shall have before\nus a vast network of pathways, all equally capable of conducting an\nexcitation, but not all equally and at all moments open. It will always\nbe difficult to determine what are the conditions which at any moment\nfavor or obstruct particular openings. Paths that have been frequently\ntraversed will of course be more readily traversed again; but this very\nfacility will _sometimes_ be an obstacle, since it will have caused\nthat path to be preoccupied, or have fatigued the organ to which it\nleads.\n\n199. Since the escape of an excitation must always be along the lines\nof least resistance, an obvious explanation of the restriction to\ncertain paths has been to assume that some fibres and cells have\nnaturally greater resistance than others. But this explanation is\nsimply a restatement of the fact in other words. What is this greater\nresistance? Why is it present in one fibre rather than in another?\nWe should first have to settle whether the resistance was in the\nnervous pathway itself, or in the centre, or in the organ innervated;\nan excitation might pass along the nervous tract, yet fail to change\nthe state of the centre, or the organ, sufficiently to produce an\nappreciable response; and only those parts where an appreciable\nresponse was produced would then be considered as having had the\npathways of propagation open.\n\n200. When we reflect on the innumerable stimulations to which the\norganism is subjected from so many various points, and remember\nfurther that _each stimulation leaves behind it a tremor which\ndoes not immediately subside_, we shall conceive something of the\nexcessive complexity of the mechanism, and marvel how any order is\nestablished in the chaos. What we must firmly establish in our minds\nis that the mechanism is essentially a _fluctuating_ one, its elements\nbeing combined, recombined, and resolved under infinite variations\nof stimulation. If it were a mechanism of fixed relations, such as\nwe find in machines, or in the \u201cmechanism of the heavens,\u201d we might\naccept the notion of certain organites having greater resistance as\na consequence of their structure, just as one muscle resists being\nmoved by the impulse which will move another. Nor is it doubtful\nthat such differences exist in nervous organites; but the laws of\ncentral excitation are not interpretable by any such hypothesis,\nsince we know that the paths which were closed against an impulse of\nconsiderable energy may be all open to an impulse of feebler energy,\nand that a slight variation in the stimulus will be followed by a wide\nirradiation. For example, a grain or two of snuff will excite the\nviolent and complex act of sneezing, but the nerves of the nasal cavity\nmay be pinched, cut, or rubbed, without producing any such result.\nOne group of nervous organites will fail to involve the activity of\nneighboring groups; and the simple movement of a single organ is then\nall that appreciably follows the stimulation; yet by a slight change in\nthe stimulation, the organites are somewhat differently grouped, and\nthe result is a complex movement of many organs. It is this fluctuation\nof combination in the organites which renders education and progress\npossible. Those combinations which have very frequently been repeated\nacquire at last an automatic certainty.\n\n       *       *       *       *       *\n\nWe are now in a position to examine with more precision the extremely\nimportant laws of nervous action which are involved in the phenomena\ndesignated by the terms Reflex Action, Automatic Action, and Voluntary\nAction.\n\n\n\n\nPROBLEM III.\n\nANIMAL AUTOMATISM.\n\n    \u201cL\u2019organisme le plus complexe est un vaste m\u00e9canisme qui r\u00e9sulte de\n    l\u2019assemblage de m\u00e9canismes secondaires.\u201d--CLAUDE BERNARD.\n\n    \u201cLes corps vivants sont machines \u00e0 l\u2019infini.\u201d--LEIBNITZ.\n\n    \u201cNoi lamentiamo con Majendie che nel linguaggio fisiologico siensi\n    intruse le preopinioni psicologiche col trascico inevitabile\n    del vocaboli, ai quali codeste preopinioni si trovano legate.\n    Probabilmente questa fu una delle principali cagioni degli errori e\n    degli equivoci anatomofisiologici, da cui non poterono svincolarsi,\n    a loro insaputa, i cultori sperimentali della scienza, perch\u00e8 nell\u2019\n    interpretare i fenomeni osservati erano obbligati ad usare il\n    linguaggio di una false moneta in corso.\u201d--LUSSANA _e_ LEMOIGNE,\n    _Fisiologia dei Centri Nervosi_, 1871, I. 16.\n\n\n\n\nANIMAL AUTOMATISM.\n\n\n\n\nCHAPTER I.\n\nTHE COURSE OF MODERN THOUGHT.\n\n\n1. Modern Philosophy has moved along two increasingly divergent lines.\nOne, traversed by Galileo, Descartes, Newton, and Laplace, had for\nits goal the absolute disengagement of the physical from the mental,\ni.\u00a0e. the objective from the subjective aspect of phenomena, so\nthat the physical universe, thus freed from all the complexities of\nFeeling, might be interpreted in mechanical terms. As a preliminary\nsimplification of the problem this was indispensable; only by it\ncould the First Notion of primitive speculation be replaced by the\nTheoretic Conception of scientific speculation.[204] The early\nthinker inevitably invested all external objects with properties and\nqualities similar to those he assigned to human beings, and their\nactions he assigned to human motives. Sun, moon, and stars seemed\nliving beings; flames, streams, and winds were supposed to be moved\nby feelings such as those known to move animals and men. Nor was any\nother conception then possible: men could only interpret the unknown\nby the known, and their standard of all action was necessarily drawn\nfrom their own actions. Not having analyzed Volition and Emotion,\nabove all not having localized these in a neuro-muscular system, men\ncould not suspect that the movements of planets and plants, and of\nstreams and stones, had motors of a different kind from the movements\nof animals. The scientific conception of inert insensible Matter was\nonly attained through a long education in abstraction; and is assuredly\nnever attained by animals, or by savages. But no sooner were vital\nconditions recognized, than the difference between vital and mechanical\nmovements emerged. When men learned that many of their own actions\nwere unaccompanied either by Love or Hate, by Pleasure or Pain, and\nthat many were unprompted by conscious intention, while others were\nunaccompanied by conscious sensation, they easily concluded that\nwherever the special conditions of Feeling were absent, the actions\nmust have some other motors. Intelligence, Emotion, Volition, and\nSensation being one by one stripped away from all but a particular\nclass of bodies, nothing remained for the other bodies but insensible\nMatter and Motion. This was the Theoretic Conception which science\nsubstituted for the First Notion. It was aided by the observation\nof the misleading tendency of interpreting physical phenomena by\nthe human standard, substituting our fancies in the place of facts,\nmanipulating the order of the universe according to our imagination\nof what it might be, or ought to be. Hence the vigilance of the new\nschool in suppressing everything pertaining to the subjective aspect\nof phenomena, and the insistance on a purely objective classification,\nso that by this means we might attain to a knowledge of things as they\nare. By thus withdrawing Life and Mind from Nature, and regarding\nthe universe solely in the light of Motion and the laws of Motion,\ntwo great scientific ends were furthered, namely, a classification\nof conceptions, and a precision of terms. Objective phenomena made a\nclass apart, and the great aim of research was to find a mathematical\nexpression for all varieties under this class. Masses were conceived\nas aggregates of Atoms, and these were reduced to mathematical points.\nForces were only different modes of Motion. All the numberless\ndifferences which perception recognized as _qualities_ in things, were\nreduced to mere variations in _quantity_. Thus all that was particular\nand concrete became resolved by analysis into what was general and\nabstract. The Cosmos then only presented a problem of Mechanics.\n\n2. During this evolution, the old Dualism (which conceived a material\nuniverse sharply demarcated from the mental universe) kept its\nground, and attained even greater precision. The logical distinction\nbetween Matter and Mind was accepted as an essential distinction,\ni.\u00a0e. representing distinct reals. There was on the one side a group\nof phenomena, Matter and Force; on the other side an unallied group,\nFeeling and Thought: between them an impassable gulf. How the two\nwere brought into relation, each acting and reacting on the other,\nwas dismissed as an \u201cinsoluble mystery\u201d--or relegated to Metaphysics\nfor such minds as chose to puzzle over questions not amenable to\nexperiment. Physics, confident in the possession of mathematical\nand experimental methods which yielded definite answers to properly\nrestricted questions, peremptorily refused to listen to any suggestion\nof the kind. And the career of Physics was so triumphant that success\nseemed to justify its indifference.\n\n3. In our own day this analytical school has begun to extend its\nmethods even to the mental group. Having reduced all the objective\ngroup to mathematical treatment, it now tries to bring the subjective\ngroup also within its range. Not only has there been more than one\nattempt at a mathematical Psychology; but also attempts to reduce\nSensibility, in its subjective no less than in its objective aspect, to\nmolecular movement. Here also the facts of Quality are translated into\nfacts of Quantity; and all diversities of Feeling are interpreted as\nsimply quantitative differences.\n\n4. Thus far the one school. But while this Theoretic Conception\nstripped Nature of consciousness, motive, and passion, rendering it a\nmere aggregate of mathematical relations, a critical process was going\non, which, analyzing the nature of Perception, was rapidly moving\ntowards another goal. Locke, Berkeley, Hume, and Kant, directing their\nanalysis exclusively to the subjective aspect of phenomena, soon broke\ndown the barriers between the physical and mental, and gradually merged\nthe former in the latter. Matter and its qualities, hitherto accepted\nas independent realities, existing where no Mind perceived them, were\nnow viewed as the creations of Mind--their existence was limited to a\nstate of the percipient. The old Dualism was replaced by Idealism. The\nCosmos, instead of presenting a problem of Mechanics, now presented a\nproblem of Psychology. Beginning with what are called the secondary\nqualities of Matter, the psychological analysis resolved these into\nmodes of Feeling. \u201cThe heat which the vulgar imagine to be in the fire\nand the color they imagine in the rose are not there at all, but are in\nus--mere states of our organism.\u201d Having gained this standing-place,\nthere was no difficulty in extending the view from the secondary to the\nprimary qualities. These also were perceptions, and only existed in\nthe percipient. Nothing then remained of Matter save the hypothetical\nunknown _x_--the postulate of speculation. Kant seemed forever to have\nclosed the door against the real Cosmos when he transformed it into\na group of mental forms--Time, Space, Causality, Quantity, etc. He\npropounded what may be called a theory of mental Dioptrics whereby a\npictured universe became possible, as Experience by its own _a priori_\nlaws moulded _itself_ into a consistent group of appearances, which\nproduced the illusion of being a group of realities. He admitted,\nindeed, that by the operation of Causality we are compelled to believe\nin a Real underlying the appearances; but the very fact that this\nCausality is a _subjective law_, is proof, he said, of its not being\nan _objective truth_. Thus the aim of the mechanical conception was\nto free research from the misleading complexities of subjective\nadulterations, and view _things as they are_ apart from their\n_appearances_; but this aim seemed illusory when Psychology showed that\nTime, Space, Matter, and Motion were themselves not objective reals\nexcept in so far as they represented subjective necessities; and that,\nin short, things _are_ just what they _appear_, since it is only in the\nrelation of external reals to internal feelings that objects exist for\nus.\n\n5. Idealism has been the outcome of the psychological method. It\nhas been of immense service in rectifying the dualistic conception,\nand in correcting the mechanical conception. It has restored the\nsubjective factor, which the mechanical conception had eliminated.\nIt has brought into incomparable clearness the fundamental fact that\nall our knowledge _springs from_, and is _limited by_, Feeling. It\nhas shown that the universe represented in that knowledge, can only\nbe a picture of the system of things as these exist in relation to\nour Sensibility. But equally with the mechanical conception it has\nerred by incomplete analysis. For a complete theory of the universe,\nor of any one phenomenon, those elementary conditions which analysis\nhas provisionally set aside must finally be restored. When Quality\nis replaced by Quantity, this is an artifice of method, which does\nnot really correspond with fact. The quality is the fact given in\nfeeling, which we analytically refer to quantitative differences,\nbut which can never be wholly resolved into them, since it must be\npresupposed throughout. One color, for example, may be distinguished\nfrom another as having more or fewer undulations; and so we may by\nabstraction, letting drop all qualitative characters, make a scale\nof undulations to represent the scale of colors. But this is an\nideal figment. It is the representation of one series of feelings by\nanother series of different feelings. No variation of undulations will\nreally correspond with variation in color, unless we reintroduce the\nsuppressed _quality_ which runs through all color. Attempt to make one\nborn blind feel, or even understand, Color by describing to him the\nkind of wave-movement which it is said to be, and the vanity of the\neffort will be manifest. Movement he knows, and varieties of movement\nas given in _tactile and muscular sensations_; but no combination and\nmanipulation of such experiences can give him the specific sensation\nof Color. That is a purely subjective state, which he is incapable of\nexperiencing, simply because one of the essential factors is absent.\nOne set of objective conditions is present, but the other set (his\nsense-organ) is defective. Without the \u201cgreeting of the spirit\u201d\nundulations cannot become colors (nor even undulations, for these\nalso are forms of feeling). Besides the sense-organ there is needed\nthe feeling of Difference, which is itself the product of past and\npresent feelings. The reproduction of other colors, or other shades of\ncolor, is necessary to this perception of difference; and this involves\nthe element of Likeness and Unlikeness between what is produced and\nreproduced. So that a certain mental co-operation is requisite even for\nthe simplest perception of quality. In fact, psychological analysis\nshows that even Motion and Quantity, the two objective terms to which\nsubjective Quality is reduced, are themselves Fundamental Signatures\nof Feeling;[205] so that here, as elsewhere, it is only by analytical\nartifice that the objective can be divorced from the subjective. Matter\n_is_ for us the Felt; its Qualities are differences of Feeling.\n\n6. Not that this result is to be interpreted as freeing our Theoretic\nConception from its objective side, and landing us in Idealism,\nwhich suppresses the real universe. The denial of all reality apart\nfrom our minds, is a twofold mistake: it confounds the conception of\ngeneral relations with particular relations, declaring that because\nthe External in its relation to the sentient organism can only be\nwhat it is felt to be, therefore it can have no _other_ relations to\nother individual reals. This is the first mistake. The second is the\ndisregard of the constant presence of the objective real in every fact\nof Feeling: the Not-Self is emphatically present in every consciousness\nof Self.\n\nThe legitimate conclusion is neither that of Dualism nor of Idealism,\nbut what I have named Reasoned Realism (_Problems_, Vol. I. p. 201),\nwhich reconciles Common Sense with Speculative Logic, by showing that\nalthough the _truth_ of things (their _Wahrheit_) is just what we\nperceive in them (our _Wahrnehmung_), yet their _reality_ is this, and\nmuch more than this. _Things_ are what they are felt to be; and what\nthey are thought to be, when thoughts are symbols of the perceptions.\nIdealism declares that they are _nothing but_ this. It is against this\n_nothing but_ that Common Sense protests; and the protest is justified\nby Reasoned Realism, which, taking a comprehensive survey of the facts,\nthus answers the idealist: \u201cYour synthesis is imperfect, since it\ndoes not include _all_ the data--notably it excludes the fact of an\nobjective or Not-Self element in every feeling. You may, conceivably,\nregard the whole universe as nothing but a series of changes in your\nconsciousness; but you cannot hope to convince me that I myself am\nsimply a change in yourself, or that my body is only a fleeting image\nin your mind. Hence although I conclude that the Not-Self is to you, as\nto me, undivorceable from Self, inalienable from Feeling, in so far as\nit is felt, yet there must nevertheless be for both of us an existence\nnot wholly coextensive with our own. _My_ world may be my picture of\nit; _your_ world may be your picture of it; but there is something\ncommon to both which is more than either--an existent which has\ndifferent relations to each. _You_ are not _me_, nor is the pictured\nCosmos _me_, although I picture it. Looking at you and it, I see a vast\nwhole of which you are a small part; and such a part I conclude myself\nto be. It is at once a picture and the pictured; at once subjective and\nobjective. To me all your modes of existence are objective aspects,\nwhich, drawing from my own experience, I believe to have corresponding\nsubjective aspects; so that your emotions, which to me are purely\nphysical facts, are to you purely mental facts. And psychological\nanalysis assures me that all _physical facts are mental facts expressed\nin objective terms_, and _mental facts are physical facts expressed in\nsubjective terms_.\u201d\n\n7. But while Philosophy thus replaces the conceptions of Dualism and\nIdealism by the conception of the Two-fold Aspect, the special sciences\nin their analytical career have disregarded the problem altogether.\nThe mechanical theory of the universe not only simplified research by\nconfining itself solely to the objective aspect of phenomena, but by\na further simplification set aside all vital and chemical relations,\nto deal exclusively with mechanical relations. In ascertaining the\nmathematical relations of the planetary system, no elucidation could\npossibly be gained from biological or chemical conceptions; the\nplanets therefore were provisionally stripped of everything not\nmechanical. In systematizing the laws of motion, it was necessary to\ndisengage the abstract relations from everything in any way resembling\nspontaneity, or extra-mechanical agency: Matter was therefore, by\na bold fiction, declared to be inert, and its Motion regarded as\nsomething superadded from without.\n\n7_a_. And this was indispensable for the construction of those ideal\nlaws which are the objects of scientific research. Science, as we often\nsay, is the systematization of Experience under the forms of ideal\nconstructions. Experience implies Feeling, and certain fundamental\nSignatures, all reducible to the primary discernment of Likeness and\nUnlikeness. Hence Science is first a _classification_ of qualities\nor discerned likenesses and differences; next a _measurement_\nof quantities of discerned likenesses and differences. Although\nmeasurement is itself a species of classification, it is distinguished\nby the adoption of a standard unit of comparison, which, being precise\nand unvarying, enables us to express the comparisons in precise and\nunvarying symbols. Whether the unit of length adopted be an inch, a\nfoot, a yard, a mile, the distance of the earth from the sun, or the\ndistances of the fixed stars, the quantities thus measured are symbols\nadmitting of one invariable interpretation. The exactness of the\nmathematical sciences is just this precision and invariability of their\nsymbols, and is not, as commonly supposed, the source of any superior\ncertainty as to the facts. The classificatory sciences, which deal with\nqualities rather than with quantities, may be equally _certain_, and\nrepresent fuller _knowledge_, because involving more varied feelings,\nbut they cannot pretend to exactness. Even on the quantitative side,\ncertainty is not identical with exactness. I may be quite certain that\none block of marble is larger than another--meaning that it affects\nme more voluminously--but I cannot know how much larger it is, without\ninterpreting my feelings by the standard of quantity--the how-muchness\nas represented by that standard. The immense advantages of exact\nmeasurement need not be insisted on. The Biological Sciences, which\nare predominantly classificatory, can never rival the Cosmological\nSciences in exactness; but they may reach a fuller knowledge; and\ntheir certainty will assume more and more the character of exactness\nas methods of measurement are applied to their classifications of\nqualities. The qualitative and quantitative aspects of phenomena are\nhandled by the two great instruments, Logic and Mathematics, the second\nbeing only a special form of the first. These determine the general\nconceptions which are derived from our perceptions, and the whole\nconstitute Experience.\n\n8. What is the conclusion to which these considerations lead? It\nis that the separation of the quantitative from the qualitative\naspect of phenomena--the objective mechanical from the subjective\npsychological--is a logical artifice indispensable to research; but\nit is only an artifice.[206] In pursuance of this artifice, each\nspecial science must be regarded as the search after special analytical\nresults; and meanwhile this method should be respected, and no\nconfusion of the boundaries between one science and another should be\nsuffered. Mechanical problems must not be confused by the introduction\nof biological relations. Biological problems must not be restricted\nto mechanical relations. I do not mean that the mechanical relations\npresent in biological phenomena are not to be sought, and, when found,\nto be expressed in mechanical terms; I mean that such an inquiry must\nbe strictly limited to mechanical relations. Subjective relations\nare not to be denied, because they are provisionally set aside, in an\ninquiry into objective relations; but we must carefully distinguish\nwhich of the two orders we are treating of, and express each in its\nappropriate terms. This is constantly neglected. For example, nothing\nis more common than to meet such a phrase as this: \u201cA _sensory\nimpression_ is transmitted as a _wave_ of _motion_ to the brain, and\nthere being transformed into a state of _consciousness_, is again\nreflected as a _motor_ impulse.\u201d\n\nThe several sciences having attained certain analytical results, it\nremains for Philosophy to co-ordinate these into a doctrine which will\nfurnish general conceptions of the World, Man, and Society. On the\nanalytical side a mechanical theory of the universe might be perfected,\nbut it would still only be a theory of mechanical relations, leaving\nall other relations to be expressed in other terms. We cannot accept\nthe statement of Descartes that Nature is a vast mechanism, and Science\nthe universal application of mathematics. The equation of a sphere,\nhowever valuable from a geometrical point of view, is useless as an\nexplanation of the nature and properties of the spherical body in\nother relations. And so a complete theory of the mechanical relations\nof the organism, however valuable in itself, would be worthless in\nthe solution of a biological problem, unless supplemented by all that\nmechanical terms are incompetent to express.\n\n9. The course of biological speculation has been similar to the\ncosmological. It also began with a First Notion, which compendiously\nexpressed the facts of Experience. Nor can any Theoretic Conception be\nfinally adopted which does away with these facts, known with positive\ncertainty, and popularly expressed in the phrase: \u201cI have a body, and\na soul.\u201d We may alter the phrase either into \u201cI _am_ a body, and I\n_am_ a soul\u201d; or into, \u201cMy body is only the manifestation of my soul\u201d;\nor, \u201cMy soul is only a function of my body\u201d; but the fundamental\nexperiences which are thus expressed are of absolute authority, no\nmatter how they may be interpreted. That I have a body, or am a body,\nis not to be speculatively argued away. That I move my arm to strike\nthe man who has offended me, or stretch out my hand to seize the fruit\nwhich I see, is unquestionable; that these movements are determined by\nthese feelings, and are never thus effected unless thus determined, is\nalso unquestionable. Here are two sets of phenomena, having well-marked\ndifferences of aspect; and they are grouped respectively under two\ngeneral heads, Life and Mind. Life is assigned to the physical\norganism, or Body--all its phenomena are objective. Mind is assigned\nto the psychical organism, or Soul--all its phenomena are subjective.\nAlthough what is called my Body is shown to be a group of qualities\nwhich are feelings--its color, form, solidity, position, motion--all\nits physical attributes being what is felt by us in consequence of\nthe laws of our organization; yet inasmuch as these feelings have the\ncharacteristic marks of objectivity, and are thereby referred to some\nobjective existence, we draw a broad line of demarcation between them\nand other feelings having the characteristic marks of subjectivity,\nand referring to ourselves as subjects. Psychological analysis shows\nus that this line of demarcation is artificial, only representing a\ndiversity of aspect; but as such it is indispensable to science. We\ncannot really separate in a sensation what is objective from what\nis subjective, and say how much belongs to the Cosmos apart from\nSensibility, and how much to the subject pure and simple; we can only\nview the sensation alternately in its objective and subjective aspects.\nWhat belongs to extra-mental existence in the phenomenon of Color,\nand what to the \u201cgreeting of the spirit,\u201d is utterly beyond human\nknowledge: for the ethereal undulations which physicists presuppose as\nthe cosmic condition are themselves subjected to this same greeting of\nthe spirit: they too are ideal forms of sensible experiences.\n\n10. This conclusion, however, was very slowly reached. The distinction\nof aspects was made the ground of a corresponding distinction in\nagencies. Each group was personified and isolated. The one group was\npersonified in Spirit--an existent in every respect opposed to Matter,\nwhich was the existent represented in the other group. One was said\nto be simple, indestructible; the other compound, destructible. One\nwas invisible, impalpable, beyond the grasp of Sense; the other was\nvisible, tangible, sensible. One was of heaven, the other of earth.\nThus a biological Dualism, analogous to the cosmological, replaced\nthe First Notion. It was undermined by advances in two directions.\nPsychology began to disclose that our conception of Matter was,\nto say the least, _saturated_ with Mind, its Atoms confessedly\nbeing ideal figments; and that all the terms by which we expressed\n_material qualities_ were terms which expressed _modes of Feeling_;\nso that whatever remained over and above this was the unknown _x_,\nwhich speculation required as a postulate. Idealism, rejecting this\npostulate, declared that Matter was simply the projection of Mind, and\nthat our Body was the objectivation of our Soul. Physiology began to\ndisclose that all the mental processes were (mathematically speaking)\n_functions_ of physical processes, i.\u00a0e. varying with the variations\nof bodily states; and this was declared enough to banish forever the\nconception of a Soul, except as a term simply expressing certain\nfunctions.\n\n11. Idealism and Materialism are equally destructive of Dualism. The\ndefects of particular idealist and materialist theories we will\nnot here touch upon; they mainly result from defects of Method. Not\nsufficiently recognizing the primary fact testified by Consciousness,\nnamely, that Experience expresses both physical and mental aspects,\nand that a Not-Self is everywhere indissolubly interwoven with Self,\nan objective factor with a subjective factor, the idealist reduces\nExistence to a mere panorama of mental states, and the Body to a\ngroup in this panorama. He is thus incapable of giving a satisfactory\nexplanation of all the objective phenomena which do not follow in the\nsame order as his feelings, which manifest a succession unlike his\nexpectation, and which he cannot class under the order of his mental\nstates hitherto experienced. He conceives that it is the Mind which\n_prescribes_ the order in Things; whereas experience assures us that\nthe order is _described_, not prescribed by us: described in terms of\nFeeling, but determined by the laws of Things, i.\u00a0e. the genesis of\nsubjective phenomena is determined by the action of the Cosmos on our\nSensibility, and the reaction of our Sensibility. He overlooks the\nevidence that the mental forms or laws of thought which determine the\ncharacter of particular experiences, were themselves evolved through a\ncontinual action and reaction of the Cosmos and the Soul, precisely as\nthe laws of organic action which determine the character of particular\nfunctions were evolved through a continual adaptation of the organism\nto the medium. These immanent laws are declared to be transcendental,\nantecedent to all such action and reaction.\n\nA similar exclusiveness vitiates the materialist doctrine. Overlooking\nthe primary fact that Feeling is indissolubly interwoven with processes\nregarded as purely physical because they are considered solely in their\nobjective aspect, the materialist fails to recognize the operation of\npsychological laws in the determination of physiological results;\nhe hopes to reduce Biology to a problem of Mechanics. But Vitality\nand Sensibility are coefficients which must render the mechanical\nproblem insoluble, if only on the ground that mechanical principles\nhave reference to quantitative relations, whereas vital relations are\nqualitative. His error is the obverse of the vitalist\u2019s error. The\nvitalist imagines that the speciality of organic phenomena proves the\nexistence of a cause which has no community with the forces operating\nelsewhere; so, turning his back on all the evidence, he attempts to\nexplain organic phenomena without any aid from Physics and Chemistry.\nThe materialist, turning his back on all the evidence of quite special\nconditions only found at work in living organisms, tries to explain\nthe problem solely by the aid of Physics and Chemistry. It is quite\ncertain that physiological and psychological problems are not to be\nsolved if we disregard the laws of Evolution through Epigenesis. The\nmental structure is evolved, as the physical structure is evolved. It\nis quite certain that no such evolution is visible in anorganisms,\nnor will any one suppose it to be possible in machines. From the\nbiological point of view we must therefore reject both Idealism and\nMaterialism. We applaud the one when it says, \u201cDon\u2019t confuse mental\nfacts by the introduction of physical hypotheses\u201d; and the other when\nit says, \u201cDon\u2019t darken physical facts with metaphysical mists.\u201d We say\nto both, \u201cBy all means make clear to yourselves which aspect of the\nphenomena you are dealing with, and express each in its own terms. But\nin endeavoring to understand a phenomenon you must take into account\nall its ascertainable conditions. Now these conditions are sometimes\nonly approachable from the objective side; at other times only from the\nsubjective side.\u201d\n\n12. While it is necessary to keep the investigation of a process on its\nobjective side, limited to objective conditions, and to express the\nresult in objective terms, we must remember that this is an artifice;\nabove all, we must remember that even within the objective limits our\nanalyses are only provisional, and must be finally rectified by a\nrestoration of all the elements we have provisionally set aside. Thus\nrectified, the objective interpretation of vital and mental phenomena\nhas the incomparable advantage of simplifying research, keeping it\nfixed on physical processes, instead of being perturbed by suggestions\nof metaphysical processes. And as all physical investigation naturally\ntends to reduce itself to a mechanical investigation, because Mechanics\nis the science of motion, and all physical processes are motions,\nwe may be asked, Why should not the mechanical point of view be the\nrational standing-point of the biologist? Our answer is, Because\nMechanics concerns itself with abstract relations, and treats of\nproducts without reference to modes of production, i.\u00a0e. with motions\nwithout reference to all the conditions on which they depend. Every\nphysical change, if expressed in physical terms, is a change of\nposition, and is determined by some preceding change of position. It\nis a movement having a certain velocity and direction, which velocity\nand direction are determined by the velocity and direction of a force\n(a pressure or a tension) compounded with the forces of resistance,\ni.\u00a0e. counter-pressures. Clearly, the nature of the forces in operation\nmust be taken into account; and it is this which the mechanical view\ndisregards, the biological regards. The mechanical view is fixed\non the ascertained adjustment of the parts, so that the working of\nthe organism may be explained as if it were a machine, a movement\nhere liberating a movement there. The biological view includes this\nadjustment of parts, but takes in also the conditions of molecular\nchange in the parts on which the adjustment dynamically depends.\nMechanical actions may be expressed as the enlargement or diminution\nof the angle of two levers; but chemical actions are not thus\nexpressible; still less vital and mental actions.\n\n13. The organism is on the physical side a mechanism, and so long\nas the mechanical interpretation of organic phenomena is confined\nto expressing the mechanical principles involved in the mechanical\nrelations, it is eminently to be applauded. But the organism is\nsomething more than a mechanism, even on the physical side; or, since\nthis statement may be misunderstood, let me say, what no one will\ndispute, that the organism is a mechanism of a very special kind, in\nmany cardinal points unlike all machines. This difference of kind\nbrings with it a difference of causal conditions. In so far as the\nactions of this mechanism are those of a dependent sequence of material\npositions, they are actions expressible in mechanical terms; but in\nso far as these actions are dependent on vital processes, they are\nnot expressible in mechanical terms. Vital facts, especially facts\nof sensibility, have factors neither discernible in machines nor\nexpressible in mechanical terms. We cannot ignore them, although for\nanalytical purposes we may provisionally set them aside.\n\n       *       *       *       *       *\n\nIn the course of the development of the mechanical theory, the history\nof which has just been briefly sketched, biological problems have more\nand more come under its influence. There has always been a fierce\nresistance to the attempt to explain vital and sentient phenomena\non mechanical, or even physical principles, but still the question\nhas incessantly recurred, How far is the organism mechanically\ninterpretable? And while the progress of Biology has shown more and\nmore the machine-like adjustment of the several parts of which the\norganism is composed, it has also shown more and more the intervention\nof conditions not mechanically interpretable. We shall have to\nconsider the question, therefore, under two forms. First, whether\nanimals are machines, and if not, by what characters do we distinguish\nthem from machines? Secondly, in what sense can we correctly speak of\nFeeling as an agent in organic processes?\n\n\n\n\nCHAPTER II.\n\nTHE VITAL MECHANISM.\n\n\n14. No answer can be successfully attempted in reply to the first\nof the questions which closed the last chapter until we have given\nprecision to certain terms of incessant recurrence. I have often\nto remark on the peculiar misfortune of Psychology, that all its\nprincipal terms are employed by different writers, and are understood\nby different readers, in widely different senses: they denote and\nconnote meanings of various significance. All physicists mean the same\nthing when they speak of weight, mass, momentum, electricity, heat,\netc. All chemists mean the same thing when they speak of affinity,\ndecomposition, oxygen, carbonic acid, etc. All physiologists mean the\nsame thing when they speak of muscle, nerve, nutrition, secretion, etc.\nBut scarcely any two psychologists mean precisely the same thing when\nthey speak of sensation, feeling, thought, volition, consciousness,\netc.; and the differences of denotation and connotation in their uses\nof such terms lead to endless misunderstanding. As Rousseau says: \u201cLes\nd\u00e9finitions pourraient \u00eatre bonnes si l\u2019on n\u2019employait pas les mots\npour les faire.\u201d But since we must employ words as our signs, our\nutmost care should be given to clearly marking what it is the signs\nsignify.\n\n15. The question we have now before us, whether animal actions are\ninterpretable on purely mechanical principles? can only be answered\nafter a preliminary settlement of the terms. The first of these\nterms to be settled is that of mechanism, when applied to the vital\norganism. If the organism is a mechanism, its actions must of course be\ninterpretable on mechanical principles. But this general truth requires\na special interpretation, if on inquiry we find that the organism is a\nparticular kind of mechanism, one which is _not_ to be classed under\nthe same head as inorganic machines. And this we do find. In Problem\nI. \u00a7 22, will be found a statement of the radical difference between\norganic and inorganic mechanisms, due to the differences in their\nstructures. But the differences there noted do not affect the operation\nof abstract mechanical principles, which are of course manifested\n_wherever_ there is a dependent sequence of material changes; and which\nare the same abstract principles in the mechanism of the heavens,\nthe mechanism of a paper-mill, or the mechanism of an animal body.\nIn other words, the principles are abstract, and are abstracted from\nall concrete cases by letting drop what is special to each case,\nretaining only what is common to all. This procedure is indispensable\nto the ideal constructions of Science. But we cannot rightly interpret\nany concrete case by abstract principles alone; we must restore the\nspecial characters which the abstraction has eliminated. The most lucid\nexplanation of the mechanism of the heavens will leave us quite in\nthe dark respecting the action of a paper-mill, until we have studied\nthe mill at work, ascertained its structure and mode of operation,\nand therein detected what is common both to its mechanism and to the\nmechanism of the heavens. Thus equipped, we approach the study of\nthe animal mechanism, but find ourselves wholly in the dark until we\nhave also ascertained its structure and mode of operation; then we\nmay recognize in it the principles of dependent sequence which had\nbeen abstracted from the paper-mill and the heavens. To neglect this\nconcrete study, and to argue from Machinery to Life in disregard\nof special conditions, is not more rational than to assume that the\nmovement of a piston is prompted by volition.\n\n16. The recognition of special differences is no denial of fundamental\nidentities. We do not deny the presence of phenomena in organisms\nwhich belong to physical and chemical agencies, but we assert that\norganisms have other phenomena besides these, dependent on conditions\nnot present in physical and chemical phenomena. The same material\nelements and forces may be recognized in a moving inorganic body,\nand a moving organic body; but in the latter there is a speciality\nof combination with a speciality of result. Just as the same words\nand laws of grammatical construction may be recognized in prose and\npoetry; yet poetry is not prose, but has special rules of its own,\nand special effects. In an organism, as in a machine, the adjustment\nof the parts is a condition of the mechanical action; the one enables\nus to explain the other. But the parts adjusted, and the consequences\nof the adjustment, are unlike in the two cases. This unlikeness is\npervading and profound. One cardinal difference is that the combination\nof the parts is in the machine a fixed, in the organism a fluctuating\nadjustment; and this fluctuation is due to certain vital processes\nsubjectively known as _sensitive guidance_. Hence machines have fixed\nand calculated mechanisms; whereas organisms are variable and to a\ngreat extent incalculable mechanisms.\n\n17. I conceive, therefore, that a theory which reduces vital activities\nto purely physical processes is self-condemned. Not that we are\nto admit the agency of any extra-organic principle, such as the\nhypothesis of Vitalism assumes (Prob. I. \u00a7 14); but only the agency\nof an intra-organic principle, or the abstract symbol of _all_ the\nco-operant conditions--the special combination of forces which result\nin organization. This assures us that an organism is a peculiar kind\nof mechanism, the processes in which are peculiar to it; and among\nthose processes there is one which results in what we call Sensibility.\nThis Sensibility is a factor which raises the phenomena into another\norder. To overlook its presence is fatal to any explanation of the\norganic mechanism. Yet it is overlooked by those who tell us that\nwhen an impression on a nerve is conveyed to the brain, and is thence\nreflected on the limbs--as when the retina of a wolf is stimulated\nby the image of a sheep, and the spring of the wolf upon the sheep\nfollows as a \u201cpurely mechanical consequence--the whole process has\nfrom first to last been physical.\u201d Unless the term _physical_ is\nhere used to designate the _objective sequence_, as contemplated by\nan onlooker, who likens the process to the sequence observable in a\nmachine, I should say that from first to last the process has been\n_not_ physical, but _vital_, involving among its essential conditions\nthe peculiarly vital factor named Sensibility. The process taking place\nin the wolf\u2019s organism is one which involves conditions never found in\npurely physical processes. We may indeed analytically disregard these.\nWe may view the process in its purely physical relations, or in its\npurely chemical relations, or in its purely mathematical (mechanical)\nrelations. But this is the artifice of the analytical method. In\nreality the process is no one of these, for it is all of these; it is a\nprocess in a living organism, and depends on conditions only found in\nliving organisms--nay, in this particular case the process depends on\nconditions only found in organisms like that of the wolf; for the image\nof the sheep will stimulate the brain of a goat, horse, or elephant\nwithout producing any such movement in the organism.\n\n18. The importance of this point must excuse my reiteration of\nit. We must make clear to ourselves that the organism is in its\nobjective aspect a physiological mechanism, in its subjective aspect\na psychological mechanism: in both aspects it is to be radically\ndemarcated from all inorganic mechanisms. In it the combination\nand co-ordination of movements involve conditions never present\nin machines; among these conditions, there are combinations and\nco-ordinations of Sensibility, which, although material processes\non the objective side, are processes believed to be only present in\norganisms. We have the strongest reasons for concluding that every\nfeeling, every change in Sensibility, has its correlative material\nprocess in the organism--is, in short, only the subjective aspect\nof the objective organic change. What in Physiology is called\nCo-ordination and has reference to movements, in Psychology may be\ncalled Logic, having reference to feelings. But be this latter point\naccepted or rejected, the one point which admits of no dispute is\nthat an organism is radically distinguishable from every inorganic\nmechanism in that _it acquires through the very exercise of its primary\nconstitution, a new constitution with new powers_. Its adjustment is a\nchanging and developing mechanism. That is to say, a machine, however\ncomplex its structure, is constructed once for all, and this primary\nconstitution is final, the adjustment of parts remaining unaltered;\nand although by exercise the machine may come to work more easily,\nwith less friction, it never comes to work differently, to _readjust_\nits parts, and develop new capabilities. It has no _historical_ factor\nmanifest in its functions. It has no experience. It reacts at last\nas at first. How different the organism! This has not only variable\nadjustments due to internal fluctuations, it has experience which\ndevelops new parts, and new adjustments of old parts. Every organism\nhas its _primary_ constitution in the adjustment of parts peculiar to\nthe species; it has also its _secondary_ or modified constitution,\nin the adjustment which has been more or less altered by individual\nexperiences; it has, thirdly, its _temporary_ constitution in the\nvariable adjustment due to the varying state of tension which results\nfrom varying stimulation.\n\n19. A word on each. There is a structural disposition of the parts\nwhich is common to large groups of organisms, so that a corresponding\nsimilarity is observable in the reactions of these organisms. Thus all\nquadrupeds use their limbs for locomotion in very similar ways; birds\nuse their wings for flight in similar ways. All vertebrates swallow\ntheir food, defend themselves, shrink when hurt, etc., in ways that are\nvery similar. In so far as their organizations are alike, their actions\nand reactions are alike. In so far as their organizations differ, their\nactions and reactions differ. The goose and the vulture are alike in\nthe main lines of structure; still more alike are duck and hen; yet,\nowing to certain unlike characters of structure, they manifest some\nmarked differences in action and reaction: the goose will starve in\nthe presence of food which the vulture gluttonously devours, and the\nvulture will refuse the vegetable food which the goose devours; the\nduck plunges into the water, the hen not only refuses to enter it,\nbut is greatly agitated when she sees the ducklings she has hatched\nplunging into it. That peculiar instincts, habits, and feelings are\nrigorously determined by peculiarities in the organism, no one doubts,\nwhen animals are in question. If this is less obvious in the case of\nmen, the reason is that there the influence of other factors somewhat\nmasks the operation of the primary constitution--these factors are the\nmodified and the temporary constitutions. Yet even in man it is true to\nsay that his feelings and actions are the result of his organization,\nnative and acquired.\n\n20. No two men are organized in all respects alike. There are\nindividual variations in structure, both native and acquired. These may\nbe too slight to be appreciable by any other test than the difference\nof reaction under similar external stimuli; but the variations in the\nsensibility to music, color, temperature, sexual influence, moral\ninfluence, etc., betray corresponding differences in the organisms.\nAny one variation in structure, seemingly trivial, may be the origin\nof well-marked diversity in physical and moral characters. Compare\nthe bull with the ox, or the predatory aggressive eagle with the\ncowardly vulture. Nor are the temporary modifications to be overlooked.\nAntoine Cros mentions the case of a patient, a young girl, suffering\nfrom congested liver and spleen, which of course altered the state\nof her blood, and thus for a time modified her constitution. Her\nmoral character was greatly altered by it. She ceased to feel any\naffection for father or mother; would play with her doll, but could\nnot be brought to show any delight in it; could not be drawn out of\nher apathetic sadness. Things which previously had made her shriek\nwith laughter, now left her uninterested. Her temper changed, became\ncapricious and violent.[207] Congestion of the lungs, if unaccompanied\nby congestion of the liver, never produces such effects, because not\nthus altering the blood. The effects of liver congestion are familiar.\nCros cites the case of a magistrate whose liver was enlarged, and whose\nskin showed a markedly bilious aspect, and in whom all affection seemed\nto be dead: he did not exhibit any perversion or violence, only want\nof emotive reaction. If he went to the theatre he could not feel the\nslightest pleasure in it. The thoughts of his home, his absent wife\nand children, were, he declared, as unaffecting to him as a problem in\nEuclid.\n\n21. Owing to the recognized dependence of peculiar instincts and modes\nof reaction on peculiarities of structure, comparative anatomists\nare quite confident, when they find a portion of a skull with two\noccipital condyles, that the animal to which this skull belonged had\nred blood-corpuscles without nuclei, and (if a female) suckled its\nyoung. If in that fragment of skull there remain a single tooth, it\nwill prove that the animal was carnivorous or herbivorous, and had, or\nhad not, retractile claws. From such data a general conclusion may be\nformed as to the instincts and habits of the animal. The data disclose\nmuch of the primary constitution, that is to say, the mechanism\nwhich the animal brought with it into the world, ready prepared to\nreact in definite ways on being stimulated. The connate mechanism\nhas correlative tendencies of reaction. Some of these tendencies are\ninevitably called into play by external conditions, and they continue\nunaltered amid great varieties of circumstances, provided none of these\nvariations directly deprive them of their appropriate stimulation.\nSuch tendencies of the connate mechanism are styled _automatic_ (an\nunfortunate metaphor, which has led to the theory of Automatism), and\ninclude, besides the visceral reactions, the more complex reactions\nof winking, breathing, swallowing, coughing, flying, walking, etc. It\nis true that we learn to walk, and learn to wink, whereas the other\nactions require no tentative efforts directed by experience; but the\nmechanism of all these actions is already laid down in the primary\nconstitution, and is inevitably called into play.\n\n22. The instincts also belong to the connate mechanism, and in the\ncourse of the normal experience of the animal inevitably come into\nplay; but, unlike the automatic tendencies of breathing, swallowing,\nand coughing, they are capable of modification, or even suppression,\nby alterations in the course of individual experience. The connate\nmechanism of the cat determines its dread of water, and its enmity\nto the dog and mouse; yet a cat will by the modifications of certain\nexperiences become as ready as an otter to take to the water, and\nbecome so fond of a dog that she will allow him to tend upon her\nkittens; and so indifferent to the mouse that she will let it run\nover her body. All this implies a new adjustment in the nervous\ncentres, with new modes of reaction on sensory impressions: the\ninherited mechanism has been modified. I need not dwell on the profound\nmodifications which the human inherited mechanism undergoes in the\ncourse of experience--how social influences and moral and religious\nteachings redirect, or even suppress, many primary tendencies; so that\n\u201cmoral habits\u201d become organized, and replace the original tendencies\nof the organism. These, when organized, become the inevitable modes\nof reaction, and are sometimes called secondarily automatic. It\nis important to recognize this organization of experiences, this\nacquisition of a secondary or modified constitution, if we would\nexplain psychological processes by physiological processes. Thus\nthe processes of Logic are automatic, they belong to the connate\nprimary mechanism, and their action is inevitable, invariable. The\nelements of a judgment, like the elements of a perception, may vary,\nand we therefore say that one judgment is false, and one perception\nincomplete; but the judging process is always the same, and the\nperceiving process is always the same. We may breathe pure air or\nimpure air, but the breathing process is in each case the same; and\njudgment is as automatic as breathing, not to be altered, not to be\nsuppressed. Again, the moral terror at wickedness of any recognized\nkind is as automatic as the instinctive terror at danger. The one has\nits roots in the primary disposition called love of approbation and\nits correlative dread of disapprobation: the social instinct. The\nother has its root in the primary disposition called \u201cinstinct of\nself-preservation,\u201d which is really the reflex shrinking from pain: the\nphysiological instinct.\n\n23. Besides the connate and acquired mechanism, we have now to consider\nthe temporary and fluctuating adjustments which represent the statical\ncondition of the organism at each moment. The automatism of the primary\nconstitution is such that previous experience and conscious effort\nare not needed; nor will any experience or any effort alter the mode\nof reaction. If a strong light falls on the eye, the iris contracts;\nif the eyeball is dry, the eyelid drops; if sound-waves beat upon the\ntympanum, the stapedius muscle contracts; if the lining of the throat\nbe tickled, the muscles involved in coughing or in vomiting contract.\nNo experience is necessary for these actions, some of which are so\ncomplicated that if we had to learn them, as we learn far simpler\nactions, the organism would perish before the power was attained. Yet\nall of these presuppose a certain normal state of the mechanism, any\nconsiderable variation in which will modify or suppress them.\n\n24. Secondarily automatic actions are those which have been acquired\nthrough experiences that have modified the organism, and produced a\nnew adjustment of parts. We learn to shield the eyes against a strong\nglare of light by raising the hand; by winking we learn to shield the\neye against an approaching body; we also learn to turn the head in the\ndirection of a sound, and to thrust away with our hands the object that\nis irritating our skin. Experience has been necessary for all these\nactions, and has finally organized the tendencies to perform them,\nso that the reaction is invariable, inevitable, unless controlled by\nthe will. If you tickle my throat, I may, or may not, push aside your\nhand; but if the inside of my throat be tickled, I must cough. Here\nwe see the difference between the automatic and secondarily automatic\nactions. The second being due to individual experience, are more or\nless controllable; and whether they are or are not controlled depends\non the condition of the nerve-centres at the moment. You may tickle my\nthroat, or irritate my skin, without causing any movement of my hands\nto thwart you, either because my nerve-centres are preoccupied by other\nstimulations, and I am not conscious of the irritation, or because I do\nnot choose to thwart you.\n\n25. It should be added that some secondarily automatic actions have\nbecome so firmly organized that we can only with great difficulty\ninterfere with them. Others never enter into consciousness, and are\ntherefore often supposed to be purely mechanical. The movement of the\neye towards the brightest light, and the convergence of the axes of\nboth eyes, are reflexes which, although involuntary and unconscious,\nare the products of education. They do not belong to the connate\nconstitution, although they are so inevitably acquired by experience\nthat they belong to every normal child. At first the infant stares with\na blank gaze, and its eyes, though moving under the stimulus of light,\nmove incoherently; the axes never converge except by accident. Very\nearly, however, the infant\u2019s eyes are observed to follow the movements\nof a bright light; and at last they acquire so certain and rapid a\npower of adjustment that the eyes shift from spot to spot, always\n\u201cfixing\u201d the object by bringing the most sensitive part of the retina\nto bear on it. The incoherent movements have become precisely regulated\nmovements. It is the same with speech. The vocal organs are exercised\nin an incoherent babble. By degrees these movements become regulated\nso as to respond definitely to definite stimuli, and words are formed,\nthen sentences, till finally fluent speech becomes in a great degree\nautomatic. The vocal muscles respond to an auditory stimulus, and the\nchild repeats the word it has heard, just as the eye-muscles respond\nto a retinal stimulus. That we acquire the power of converging the\naxes, and accommodating the lens to near objects, is not only proved by\nobservation of infants, but also by cases of disease. After the reflex\nmechanism has been long established, so that it acts with inevitable\nprecision, a slight paralysis of one of the muscles has the effect of\nmaking all objects appear in a different position; the patient trying\nto touch an object, then always moves his hand on one side of it. Von\nGraefe relates the case of a stonebreaker who always struck his hand\nwith the hammer when he tried to strike the stone. Yet this very man\n_learned_ to accommodate his movements to the new impressions; so that\nif his paralysis had been cured, his modified mechanism would have been\nill adapted to the new conditions, and he would once more have struck\nhis hand instead of the stone.\n\n26. This digression on the native and acquired dispositions of the\norganism, while it has brought into strong light all that can be cited\nin favor of regarding animal bodies as mechanisms, and their actions\nas the direct consequences of mechanical adjustments, has also made\nconspicuous the radical difference between an organism and a machine.\nWe cannot too emphatically insist on this radical difference. Between\nthe group of conditions involved in the structure and action of a\nmachine, and the group of conditions involved in the structure and\naction of an organism, there are contrasts as broad as any that can be\nnamed. To overlook these in taking account solely of the conditions\ncommon to both groups is a serious error. On such grounds we might\ninsist that a tiger is a violet, because both are organisms.\n\nThe biologist will admit that an organism is a mechanism, and (in\nso far as its bodily structure is concerned) a material mechanism.\nAll the actions of this structure are therefore mechanical, in the\ntwo senses of the term: first, as being the actions of material\nadjustments; secondly, as being movements, and thereby included under\nthe general laws of motion represented in Mechanics; the abstract\nlaws of movement for an organic body are not different from the\nabstract laws of movement for an inorganic body. So far we have been\nconsidering the abstract relations only. No sooner do we consider the\nphenomena as concrete wholes, than we find great diversity in the modes\nof production of the movements in organisms and machines. Now it is\nprecisely the modes of production which have interest for us. We never\nunderstand a phenomenon so as to gain any practical control over it, or\nany theoretical illumination from it, unless we have mastered some of\nits conditions; our knowledge of these conditions is the measure of our\npower.\n\n\n\n\nCHAPTER III.\n\nTHE RELATION OF BODY AND MIND.\n\n\n27. The second question proposed was, In what sense can Feeling be\ncorrectly spoken of as an Agent in organic processes? This brings\nus face to face with a much-debated topic, the relation of Body and\nMind; and demands a theoretic interpretation of that First Notion\nwhich expresses universal experience, namely, that what I know as\nMyself is a Body, in one aspect, and a Soul, in the other. What I\ncall my Body is a persistent aggregate of objective phenomena; and\nmy Soul is a persistent aggregate of subjective phenomena: the one\nis an individualized group of experiences expressible in terms of\nMatter and Motion, and therefore designated _physical_; the other an\nindividualized group of experiences expressible in terms of Feeling,\nand therefore designated _psychical_. But, however contrasted, they\nare both simply embodiments of Experience, that is to say, are Modes\nof Feeling. All Existence--as known to us--is the Felt. The laws of\nour organism compel us, indeed, to postulate an Existent which is\n_extra mentem_--a Real not Ourselves--but the same laws debar us from\nany knowledge whatever of what this _is_, or is _like_. We know Things\nabsolutely _in so far_ as they exist in relation to us; and that is the\nonly knowledge which can have any possible significance for us.\n\n28. It is impossible for me to doubt that I am a Body, though I may\ndoubt whether what is thus called is anything more than a group of\nfeelings. It is impossible for me to doubt that I am a Soul; though\nI may doubt whether what is thus called is more than a group of\nbodily functions. In separating what is unquestionable from what is\nquestionable, we separate the fundamental facts of consciousness\nfrom the theoretic interpretations of those facts: no theoretic\ninterpretation can efface or alter the facts. Whatever Philosophy may\ndiscover, it cannot displace the fact that I know I am a Soul, _in\nevery sense in which that phrase represents Experience_: I know the\nSoul in knowing its concretes (feelings), and in knowing it as an\nabstraction which condenses those concretes in a symbol. The secondary\nquestion is, Whether this abstraction represents one Existent, and the\nabstraction Body another and wholly different Existent, or the two\nabstractions represent only two different Aspects? this may be debated,\nand must be answered according to theoretic probabilities.\n\n29. What are the probabilities? We are all agreed that Consciousness\nis the final arbiter. Its primary deliverance is simply that\nof _a_ radical distinction. It is silent on the nature of the\ndistinction--says nothing as to whether the distinction is one of\nagents or of aspects. It says, \u201cI am a Soul.\u201d With equal clearness\nit says, \u201cI am a Body.\u201d It does _not_ say, \u201cI am two things.\u201d Nor\ndoes the fact of a radical distinction imply more than a contrast of\naspects, such as that of convex and concave. The curve has at every\npoint this contrast of convex and concave, and yet is the identical\nline throughout. A mental process is at every point contrasted with\nthe physical process assumed to be its correlate; and this contrast\ndemands equivalent expression in the terms of each. The identity\nunderlying the two aspects of the curve is evident to Sense. The\nidentity underlying the mental and physical process is not evident to\nSense, but may be made eminently _probable_ to Speculation, especially\nwhen we have explained the grounds of the difference, namely, that they\nare apprehended through different modes. But although I admit that\nthe conclusion is only one of probability, it is one which greatly\ntranscends the probability of any counter-hypothesis. Let us see how\nthis can be made out.[208]\n\n30. We start from the position that a broad line of demarcation must\nbe drawn between the mental and the physical aspect of a process,\nsupposing them to be identical in reality. Nothing can be more _unlike_\na logical proposition than the physical process which is its correlate;\nso that Philosophy has hitherto been forced to forego every attempt at\nan explanation of how the two can be causally connected: referring the\nconnection to a mystery, or invoking two different agents, spiritual\nand material, moving on parallel lines, like two clocks regulated to\nwork simultaneously. But having recognized this difference, can we not\nalso discern fundamental resemblances? First and foremost, we note\nthat there is common to both the basis in Feeling: they are both modes\nof Consciousness. The Mind thinking the logical proposition is not,\nindeed, in the same _state_ as the Mind picturing the physical process\nwhich is the correlate of that logical proposition--no more than I,\nwho see you move on being struck, have the same feelings as you who\nare struck. But the Mind which pictures the logical proposition as\na process, and pictures the physical process as a bodily change, is\ncontemplating one and the same event under its subjective and objective\naspects; just as when I picture to myself the feelings you experience\non being struck I separate the subjective aspect of the blow from its\nobjective aspect. Secondly, between the logical proposition and the\nphysical process there is a community of causal dependence, i.\u00a0e. the\nmode of grouping of the constituent elements, whereby this proposition,\nand not another, is the result of this grouping, and not another. In\nfact, what in subjective terms is called Logic, in objective terms is\nGrouping.\n\n31. Let us approach the question on a more accessible side. Sensation\navowedly lies at the basis of mental manifestations. Now, rightly\nor wrongly, Sensation is viewed alternately as a purely subjective\nfact--a psychological process--and as a purely objective fact--the\nphysiological reaction of a sense-organ. It is so conspicuously a\nphysiological process that many writers exclude it from the domain\nof Mind, assign it to the material organism, and believe that it is\nexplicable on purely mechanical principles. This seems to me eminently\ndisputable; but the point is noticed in proof of the well-marked\nobjective character which the phenomenon assumes. In this aspect a\nsensation is simply the reaction of a bodily organ. The physiologist\ndescribes how a stimulus excites the organ, and declares its reaction\nto be the sensation. Thus viewed, and expressed in terms of Matter\nand Motion, there is absolutely nothing of that subjective quality\nwhich characterizes sensation. Yet without this quality the objective\nprocess cannot be a sensation. Exclude Feeling, and the excitation of\nthe auditory organ will no more yield the sensation of Sound by its\nreaction, than the strings and sounding-board of a piano when the keys\nare struck will yield music to a deaf spectator. Hence the natural\ninference has been that inside the organism there is a _listener_: the\nSoul is said to listen, transforming excitation into sensation. This\ninference only needs a more systematic interpretation and it will\nrepresent the biological theory, which demands something _more_ than\nthe reaction of the sensory organ--namely, the reaction of the whole\norganism _through_ the sensory organ. I mean, that no organ isolated\nfrom the organism is capable of a _physiological_ reaction--only\nof a physico-chemical reaction; and sensation depends on (_is_)\nthe physiological reaction. When a sense-organ is stimulated, this\nstimulation is a vital process, and is raised out of the class of\nphysico-chemical processes by virtue of its being the indissoluble\npart of a complex whole. Interfere with any one of the co-operant\nconditions--withdraw the circulation, check respiration, disturb\nsecretion--and the sense-organ sinks from the physiological to the\nphysical state; it may then be brought into contact with its normal\nstimuli, but no stimulation (in the vital sense) will take place, there\nwill be no vital reaction.\n\nCondensing all vital processes in the symbol Vitality, we may say\nVitality is requisite for every physiological process. A parallelism\nmay be noted on the subjective side: all the sentient processes may be\ncondensed in the one symbol Sensibility (Feeling), and we must then\nsay, No psychological process is possible as an isolated fact, but\ndemands the co-operation of others--it is a _resultant_ of all the\ncontemporaneous conditions of Sensibility in the organism. In ordinary\nlanguage this is what is meant by saying that no impression can become\na sensation without the intervention of Consciousness--an ambiguous\nphrase, because of the ambiguity of the term Consciousness, but the\nphrase expresses the fact that in Sensation a process in the organism\nis necessary to the reaction of the organ.\n\n32. Having recognized the distinction between the two processes\nobjective and subjective, physical and mental, we have recognized\nthe vanity of attempting to assign their limits, and to say where\nMotion ends and Feeling begins, or how Feeling again changes into\nMotion. The one does _not_ begin where the other ends. According to the\ntwo-clock theory of Dualism, the two _agents_ move on parallel lines.\nOn the theory of Monism the two _aspects_ are throughout opposed. Both\ntheories explain the facts; which explanation is the most congruous\nwith experience? Against the first we may object that the hypothesis of\ntwo Agents utterly unallied in nature wants the cardinal character of\na fertile hypothesis in its unverifiableness: it may be true, we can\nnever know that it is true. By the very terms of its definition, the\nSpirit--if that mean _more_ than an abstract expression of sentient\nstates--is beyond all sensible experience. This is indeed admitted by\nthe dualists, for they postulate a Spirit merely because they cannot\notherwise explain the phenomena of Consciousness. Herein they fail to\nsee that even their postulate brings no explanation, it merely restates\nthe old problem in other terms.\n\n33. Up to the present time these same objections might have been urged\nwith equal force against Monism. Indeed, although many philosophers\nhave rejected the two-clock theory of Leibnitz, they have gained a very\nhesitating acceptance for their own hypothesis of identity. To most\nminds the difficulty of imagining how a physical process could _also_\nbe a psychical process, a movement also be a feeling, seemed not less\nthan that of imagining how two such distinct Agents as Matter and Mind\ncould co-operate, and react on each other, or move simultaneously on\nparallel lines. Although for many years I have accepted the hypothesis\nof Monism, I have always recognized its want of an adequate reply to\nsuch objections. Unless I greatly deceive myself, I have now found\na solution of the main difficulty; and found it in psychological\nconditions which are perfectly intelligible. But knowing how easily one\nmay deceive one\u2019s self in such matters, I will only ask the reader to\nmeditate with open-mindedness the considerations now to be laid before\nhim, and see if he can feel the same confidence in their validity.\n\n34. One of the early stages in the development of Experience is the\nseparation of Self from the Not-Self. I look out on \u201cthe vast extern\nof things,\u201d and see a great variety of objects, included in a visible\nhemisphere. All these objects in various positions, having various\nforms and colors, I believe to be wholly detached from, and in every\nway unallied to, Myself. And what is that Self? It is my Body as a\nvisible and tangible object, separated from all other visible and\ntangible objects by the constant presence of feelings connected with\nit and its movements, and not connected with the other objects. This\nconstant presence of feelings is referred to a Soul, which I then\nseparate from my Body, as an Inner Self; and from this time onwards I\nspeak of the Body as _mine_, and learn to regard it in much the same\nlight as other outer objects. In my na\u00efve judgment the external objects\nare supposed to exist _as_ I see and touch them, whether I or any one\nelse see and touch them or not: they in no sense belong to the series\nof feelings which constitute the Me. And since my Body resembles these\nobjects in visible and tangible qualities, and also in being external\nto my feelings, it also takes its place in the objective world. Thus\narises the hypothesis of Dualism which postulates a _Physis_, or\nobject-world, and an _\u00c6sthesis_, or subject-world: two independent\nexistents, one contemplated, the other contemplating.\n\n35. Philosophy, as we know, leads to a complete reversal of this\nprimitive conclusion, and shows that the _contemplated_ is a _synthesis\nof contemplations_, the Physis being _also_ the \u00c6sthesis. Psychological\ninvestigation shows that the objects supposed to _have_ forms,\ncolors, and positions within an external hemisphere, have these\nonly in virtue of the very feelings from which they are supposed\nto be separated. The _visible_ universe exists only _as seen_: the\nobjects are Reals conditioned by the laws of Sensibility. The space\nin which we see them, their geometrical relations, the light and\nshadows which reveal them, the forms they affect, the lines of their\nchanging directions, the qualities which distinguish them,--all these\nare but the externally projected signs of feelings. They are signs\nwhich we interpret according to organized laws of experience; each\nsign being itself a feeling connected with other feelings. We project\nthem outside according to the \u201claw of eccentric projection\u201d--which is\nonly the expression of the fact that one feeling is a sign of some\nother, and is thereby _ideally detached_ from it. According to this\nlaw I say, \u201cmy Body\u201d; just as I say, \u201cmy House\u201d; or, \u201cmy Property.\u201d\nMisled by this, Dualism holds that in the very fact of detaching my\nBody from my Self, calling it _mine_, is the revelation of a distinct\nentity within the body. But that this is illusory, appears in the\napplication of this same law of eccentric projection to sensations\nand thoughts, which are called _mine_, as my legs and arms are mine.\nIf it is undeniable that I say _my_ Body--and thus ideally detach the\nBody from the Soul--it is equally undeniable that I say _my_ Soul; and\nfrom what is the Soul detached? In presence of this difficulty, the\nmetaphysician may argue that neither Body nor Soul can be coextensive\nwith its manifestations, but demands a noumenal Real for each--a\n_substratum_ for the bodily manifestations, and a _substratum_ for the\nmental manifestations. This, however, is an evasion, not a solution of\nthe difficulty. If we postulate an unknown and unknowable noumenon,\nwe gain no insight: first, because Philosophy deals only with the\nknown functions of unknown quantities, and therefore leaves the _x_\nout of the calculation; secondly, because, granting the existence of\nthese noumena, we can have no rational grounds for asserting that they\nare not of one and the same nature; for we have no grounds for _any_\nassertion whatever about them. And if it be urged against this, that\nConsciousness testifies to a distinction, I answer that on a closer\nscrutiny it will be found to testify to nothing more than a diversity\nof manifestation. All therefore that comes within the range of\nknowledge is, How does this diversity arise?\n\n36. There are two ways, and there are only two, in which differences\narise. These are, 1\u00b0, the _modes of production_ of a product, and,\n2\u00b0, our _modes of apprehension_ of the product. Things may be very\ndifferent, and yet to our apprehension indistinguishable, so that\nwe regard them as identical; and they may be identical, yet appear\nutterly unlike. A mechanical bird may seem so like a living bird, and\ntheir actions so indistinguishable to the spectator, that he will not\nsuspect a difference, or suspecting it, will not be able to specify\nit. Of both objects, so long as his modes of apprehending them are\ncircumscribed, he can only say what these imply: he sees familiar\nforms, colors, and movements, which he interprets according to the\nprevious experiences of which these are the signs. But by varying the\nmodes of apprehension, and gaining thus a fuller knowledge, he finds\nthat the two products have very different modes of production; hence he\nconcludes the products to be different: the mechanism of the one is not\nthe organism of the other; the actions of the mechanical bird are not\nthe actions of the living bird. The fuller knowledge has been gained\nby viewing the objects under different relations, and contemplating\nthem _in_ their modes of production, not as merely visible products. He\nsees the mechanism performing by steel springs, wheels, and wires, the\nwork which the organism performs by bones, muscles, and nerves; and the\nfarther his analysis of the modes of production is carried, the greater\nare the differences which he apprehends.\n\n37. Now consider the other side. One and the same object will\nnecessarily present very different aspects under different subjective\nconditions, since it is _these_ which determine the aspect. The object\ncannot be to Sight what it is to Hearing, to Touch what it is to\nSmell. The vibrations of a tuning-fork are seen as movements, heard\nas sounds. In current language the vibrations are said to cause the\nsounds. Misled by this, philosophers puzzle themselves as to how a\nmaterial process (vibration) can be transformed into a mental process\n(sensation), how such a cause can have so utterly different an effect.\nBut I have formerly[209] argued at some length that there is no\ntransformation or causation of the kind supposed. The tuning-fork--or\nthat Real which in relation to Sense is the particular object thus\nnamed--will, by one of its modes of acting on my Sensibility through\nmy optical apparatus, determine the response known as _vibrations_;\nbut it is not this response of the optical organ which is transformed\ninto, or causes the response of the auditory organ, known as _sound_.\nThe auditory organ knows nothing of vibrations, the optical nothing of\nsounds. The responses are both modes of Feeling determined by organic\nconditions, and represent the two different relations in which the\nReal is apprehended. The Real _is_ alternately the one and the other.\nAnd if the one mode of Feeling has a physical significance, while the\nother has a mental significance, so that we regard the vibrations as\nobjective facts, belonging to the external world, and the sounds as\nsubjective facts, exclusively belonging to the internal world, this is\ndue to certain psychological influences presently to be expounded.\nMeanwhile let us fix clearly in our minds that both vibrations and\nsounds are modes of Feeling. My consciousness plainly assures me\nthat it is I who see the one, and hear the other; not that there are\ntwo distinct subjects for the two distinct feelings. Add to which,\nmanifold uncontradicted experiences assure me that the occasional\ncause--the objective factor--of the one feeling, is also the cause of\nthe other, and not that the two feelings have two different occasional\ncauses. From both of these undeniable facts we must conclude that the\ndifference felt is simply a difference of aspect, determined by some\ndifference in the modes of apprehension.\n\n38. Assuming then that a mental process is only another aspect\nof a physical process--and this we shall find the more probable\nhypothesis--we have to explain by what influences these diametrically\nopposite aspects are determined. From all that has just been said we\nmust seek these in the modes of apprehension. There can be no doubt\nthat we express the fact in very different terms; the question is,\nWhat do these terms _signify_? Why do we express one aspect in terms\nof Matter and Motion, assigning the process to the objective world;\nand the other aspect in terms of Feeling, assigning the process to the\nsubjective world?\n\nLet the example chosen be a logical process as the mental aspect,\nand a neural process as its physical correlate. The particular\nproposition may be viewed logically, as a grouping of experiences,\nor physiologically, as a grouping of neural tremors. Here we have\nthe twofold aspect of one and the same reality; and these different\naspects are expressed in different terms. We cannot be too rigorous\nin our separation of the terms; for every attentive student must have\nnoted how frequently discussions are made turbid by the unconscious\n_shifting of terms_ in the course of the argumentation. This is not\nonly the mistake of opponents who are unaware of the shifting which has\noccurred in each other\u2019s minds, so that practically the adversaries\ndo not meet on common ground, but cross and recross each other; it is\nalso the mistake of the solitary thinker losing himself in the maze\nof interlacing conceptions instead of keeping steadily to one path.\nOnly by such shifting of terms can the notion of the physical process\ncausing, or being transformed into, the mental process for a moment\ngain credit; and this also greatly sustains the hypothesis of Dualism,\nwith its formidable objections: How can Matter think? How can Mind act\non Matter causing Motion?\n\n39. Those who recognized that the terms Matter and Mind were\nabstractions mutually exclusive, saw at once that these questions,\ninstead of being formidable, were in truth irrational. To ask if\nMatter could think, or Mind move Matter, was a confusion of symbols\nequivalent to speaking of a yard of Hope, and a ton of Terror. Although\nMeasure and Weight are symbols of Feeling, and in _this_ respect are\non a par with Hope and Terror, yet because they are objective symbols\nthey cannot be applied to subjective states, without violation of the\nvery significance they were invented to express. No one ever asks\nwhether a sensation of Sound can be a sensation of Color; nor whether\nColor can move a machine, although Heat can, yet the one is no less a\nsensation than the other. On similar grounds no one should ask whether\nMatter can think, or Mind move Matter. The only rational question is\none preserving the integrity of the terms, namely, whether the living,\nthinking organism presents itself to apprehension under the twofold\naspect--now under the modes of Feeling classified as objective or\nphysical; now under the modes classified as subjective or mental.\n\n40. We are told that it is \u201cimpossible to imagine Matter thinking,\u201d\nwhich is very true; only by a gross _confusion_ of terms can Thought\nbe called a property of cerebral tissue, or of Matter at all. We\nmay, indeed, penetrate beneath the terms which relate to aspects,\nand recognize in the underlying reality not two existences, but one.\nOur conceptions of this reality, however, are expressed in symbols\nrepresenting different classes of feelings, objective and subjective;\nand to employ the terms of one class to designate the conceptions of\nthe other is to frustrate the very purposes of language. Matter and\nMind, Object and Subject, are abstractions from sentient experiences.\nWe know them as abstractions, and know the concrete experiences from\nwhich they are abstracted. Philosophers, indeed, repeatedly assure us\nthat we neither know what Matter is nor what Mind is, we only know the\n_phenomenal products_ of the action and reaction of these two unknown\nnoumena. Were this so, all discussion would be idle; we could not say\nwhether Matter was or was not capable of thinking, whether Mind was or\nwas not the same as Matter, we could only abstain from saying anything\nwhatever on the topic. What should we reply to one who asked us to\nname the product of two unknown quantities? So long as _x_ and _y_ are\nwithout values their product must be without value. If the value of\n_x_ be known, and that of _y_ unknown, then the product still remains\nunknown: _x_ + _y_ = _x_ + 0 = _x_. Therefore, unless the Objective\naspect were the _equivalent_ of the Subjective aspect, it could never\nbe subjectively present. Feeling is but another aspect of the Felt.\n\n41. It is because we do know what Matter is, that we know it is\n_not_ Mind: they are symbols of two different modes of Feeling. If\nwe separate the conception of citizenship from the conception of\nfatherhood, although the same man is both citizen and father, how much\nmore decisively must we separate the conception of Matter, which\nrepresents one group of feelings, from the conception of Mind, which\nrepresents another? One element in the former is common to the whole\ngroup, namely, the reference to a Not-Self, induced by the sensation of\nResistance, which always ideally or sensibly accompanies the material\nclass. The axiom, I feel, _ergo_ I exist, has its correlative:--I act,\n_ergo_ there are other existents on which I act; and these are not\nwholly Me, for they resist, oppose, exclude me; yet they are also one\nwith Me, since they are felt by me. In my Feeling, that which is not Me\nis Matter, the objective aspect of the Felt, as Mind is the subjective\naspect.\n\nBut since Hunger and Thirst, Joy and Grief, Pain and Terror, are also\n_felt_, yet are never classed under the head of Matter, the grounds of\nthe classification of feelings have to be expressed. Professor Bain\nmakes the distinction between Matter and Mind to rest solely on the\npresence or absence of Extension: this is the decisive mark: Matter\nhe defines as the Extended. The definition is inadequate. When I see\na dog and its image reflected in a pool, or see a dog and think of\nanother, in the three cases dog, image, and idea have Extension; but\nI recognize the dog as a material fact, the idea as a mental fact;\nand although the image of the dog has material conditions by which\nI am optically affected, just as the idea has material cerebral\nconditions, I recognize a marked difference between them and the dog,\ndue to the different modes of apprehension. The dog is known as a\npersistent reality, which, when Sight is supplemented by Touch, will\nyield sensations of Resistance, and thus disclose its materiality. The\nimage vanishes if I attempt to touch it; I see its outlines waver and\nbecome confused with every disturbance of the surface of the pool;\nthe idea vanishes when another idea arises; whence I conclude that\nneither has material reality, because neither has the Resistance which\ncharacterizes the Not-Self. The image and the idea may be referred to\nmaterial conditions, but so may pains, terrors, volitions, yet these\nare all without Extension, simply because they are not visual feelings.\n\n42. Matter does not represent all feelings, but only the objective\nsensibles; and these are not all characterized by Extension, but only\nthose which directly or indirectly involve optico-tactical experiences\naccompanied by muscular experiences. Matter is primarily the Visible\nand Resistant; and secondarily, whatever can be imagined as such;\nso that ether, molecules, and atoms, although neither visible nor\ntangible, are ranged under the head of Matter. Color is a feeling as\nSound and Scent are feelings, and although material conditions are\nequally presupposed in all three, yet Color alone has Extension, and\nbecause it can be imaged it has a more objective character than the\nothers, which having no lines and surfaces, want the optical conditions\nfor the formation of images, and are less definitely connected with\ntactical and muscular experiences. Nevertheless, since Sound and Scent\nare obviously associated with objects seen and touched, they have a\ndegree of materiality never assigned to such feelings as Hunger and\nThirst, Pleasure, Terror, and Hope.\n\n43. When we refer feelings to material conditions, we follow the\nnatural tendency to translate the little known in terms of the better\nknown, and employ the symbols Matter and Motion, because these furnish\nthe intellect with images, i.\u00a0e. definite and exact elements to operate\nwith. In hearing a sound, there is nothing at all like \u201cvibrations,\u201d\nnothing like \u201caerial waves\u201d and \u201cneural processes,\u201d given in that\nfeeling; but on attempting to _explain_ it, we remove it from the\nsphere of Sensation to carry it into the sphere of Intellect, and\nwe must change our symbols in changing our problem; here our only\nresource is to translate the subjective state into an _imaginable_\nobjective process, which can only be expressed in terms of Matter\nand Motion. What we _heard_ as Sound is then _seen_ as Vibration.\nWhen we are optically or mentally contemplating vibrations and neural\nprocesses, we are supplanting one source of feeling by another,\ntranslating an event in another set of symbols. But we can no more hear\nthe sound in seeing the vibrations, than a blind man can see the fly\nin the amber which he feels with his fingers, or than we can feel the\namber he holds, while we are only looking at it. The phrase \u201cmaterial\nconditions of Feeling\u201d sometimes designates the objective aspect of the\nsubjective process, and sometimes the agencies in the external medium\nwhich co-operate with the organism in the production of the feelings.\nIn each case there is an attempt to explain a feeling by intelligible\nsymbols.\n\n44. The Animal probably never attempts such explanation; satisfied with\nthe facts, it is careless of their factors. Man is never satisfied:\nis restless in the search after factors; and having found them, seeks\nfactors of these factors; so that Lichtenberg felicitously calls him\n\u201c_das rastlose Ursachenthier_\u201d--\u201cthe animal untiring in the search\nfor causes.\u201d And thus sciences arise: we translate experiences into\ngeometrical, physical, chemical, physiological, and psychological\nterms--different symbols of the different modes of apprehending\nphenomena.\n\n45. \u201cI see an elephant.\u201d In other words, I am affected in a certain\nway, and interpret my affection by previous similar experiences,\nexpressing these in verbal symbols. But I want an explanation, and\nthis the philosopher vouchsafes to me by translating my affection into\nhis terms. He takes me into another sphere--tells me of an undulating\nEther, the waves of which beat upon my retina--of lines of Light\nrefracted by media and converged by lenses according to geometric\nlaws--of the formation thereby of a tiny image of the gigantic elephant\non my retina as on the plate of a camera-obscura--this, and much\nmore, is what _he_ sees in _my_ visual feeling, and he bids me see it\nalso. Grateful for the novel instruction, I am compelled to say that\nit does not alter my vision of the elephant, does not make the fact\na whit clearer, does not indeed correspond with what I feel. It is\noutside knowledge, valuable, as all knowledge is, but supplementary.\nIt is translation into another language. And when I come to examine\nthe translation, I find it very imperfect. I ask my instructor: Is\nit the tiny image on my retina which I see, and not the big elephant\non the grass? And how do I see this retinal image, which you explain\nto be upside down?--how is it carried from my retina to my mind? I\nhave no consciousness of tiny reversed image, none of my retina,\nonly of a fact of feeling, which I call \u201cseeing an elephant.\u201d The\ncamera-obscura has no such feeling--it reflects the image, it does\nnot see the object. Here my instructor, having reached the limit\nof his science,[210] hands me over to the physiologist, who will\ntranslate the fact for me in terms not of Geometry, but of Anatomy\nand Physiology. The laws of Dioptrics cease at this point: the image\nthey help to form on the retina is ruthlessly dispersed, and all its\nbeautiful geometric construction is lost in a neural excitation, which\nis transmitted through semifluid channels of an optic tract to a\nsemifluid ganglion, whence a thrill is shot through the whole brain,\nand is there _transformed_ into a visual sensation. Again I fancy I\nhave gained novel instruction of a valuable kind; but it does not\naffect my original experience that I am enabled to translate it into\ndifferent terms; the less so because I cannot help the conviction that\nthe translation is imperfect, leaving out the essential points. If a\nphrase be translated for me into French or German, I gain thereby an\naddition to my linguistic knowledge, but the experience thus variously\nexpressed remains unaffected. When the fact is expressed in geometrical\nor physiological terms, the _psychical process_ finds no adequate\nexpression. Neither in the details, nor in the totals, do I recognize\nany of the qualities of my state of feeling in seeing the elephant.\nI do not see the geometrical process, I do not see the anatomical\nmechanism, I see the elephant, and am conscious only of that feeling.\nYou may consider my organism geometrically or anatomically, and bring\nit thus within the circle of objective knowledge; but my subjective\nexperience, my spiritual existence, that of which I am most deeply\nassured, demands another expression. Nay more, on closely scrutinizing\nyour objective explanations, it is evident that a psychical process\nis _implied_ throughout--such terms as undulations, refractions,\nmedia, lenses, retina, neural excitation, overtly refer, indeed, to\nthe material objective aspect of the facts, but they are themselves\nthe modes of Feeling by which the facts are apprehended, and would not\nexist _as such_ without the \u201cgreeting of the spirit.\u201d\n\n46. What, then, is our conclusion? It is, that to make an adequate\nexplanation of psychical processes by material conditions we must first\nestablish an equivalence between the subjective and objective aspects;\nand, having taken this step, we must complete it by showing wherein the\ndifference exists; having established this entity and diversity, we\nhave solved the problem.\n\nLet us attempt this solution. When I speak to you, the spoken words\nare the same to you and to me. You hear what I hear, you apprehend\nwhat I apprehend. But there were muscular movements of articulation\nfelt by me and not felt by you; to feel these you also must articulate\nthe words; but so long as you merely hear the words, there is a\ndifference in our states of feeling. Some of my movements you can see,\nothers you can imagine; but this is not my feeling of them, it is your\noptical equivalent of my muscular feeling. On a similar assumption of\nequivalence, a neural process is made to stand for a logical process.\nIn thinking a proposition, we are logically grouping verbal symbols\nrepresentative of sensible experiences; and this is a quite peculiar\nstate of Consciousness, wholly unlike what would arise in the mental or\nvisual contemplation of the neural grouping, which is its physiological\nequivalent. But this diversity does not discredit the idea of their\nidentity; and although some of my readers will protest against such an\nidea, and will affirm that the logical process is not a process taking\nplace in the organism at all, but in a spirit which uses the organism\nas its instrument, I must be allowed in this exposition to consider\nthe identity established, my purpose being to explain the diversity\nnecessarily accompanying it. Therefore, I say, that although a logical\nprocess is identical with a neural process, it must appear differently\nwhen the modes of apprehending it are different. While you are thinking\na logical proposition, grouping your verbal symbols, I, who mentally\n_see_ the process, am grouping a totally different set of symbols: to\nyou the proposition is a subjective state, i.\u00a0e. a _state_ of feeling,\nnot an _object_ of feeling: to become an object, it must be apprehended\nby objective modes: and this it can become to you as to me, when we see\nit as a process, or imagine it as a process. But obviously your state\nin seeing or imagining the process must be different from your state\nwhen the process itself is passing, since the modes of apprehension\nare so different. There may be every ground for concluding that a\nlogical process has its correlative physical process, and that the two\nprocesses are merely two aspects of one event; but because we cannot\napprehend the one aspect as we apprehend the other, cannot _see_ the\nlogical sequence as we _see_ the physical sequence, this difference in\nour modes of apprehension compels us to separate the two, assigning\none to the subjective, the other to the objective class. Between the\nsensible perception of an object and the reproduced image of the object\nthere is chiefly a quantitative difference in the physiological and\npsychological processes: the image is a faint sensation. Yet this\nquantitative difference brings with it the qualitative distinction\nwhich is indicated in our calling the one a sensation, the other a\nthought. The consequence has been that while all philosophers have\nadmitted the sensation to be--at least partly--a process in the bodily\norganism, the majority have maintained that the thought is no such\nprocess in the organism, but has its seat in a spirit independent of\nthe organism.\n\n47. The states of Feeling which are associated with other states\ncharacterized as objective because overtly referring to a Not-Self, we\ngroup under the head of Matter: we assign material conditions as their\nantecedents. Whereas states of Feeling which are not thus associated we\ngroup under the head of Mind, and assign internal conditions as their\nantecedents. Color and Taste are very different states of Feeling, yet\nboth are spontaneously referred to external causes, because they are\nassociated with visual and tactical states; whereas Hunger, Nausea,\nHope, etc., have no such associations, and their material conditions\nare only theoretically assigned.\n\nOur intelligible universe is constructed out of the elements of Feeling\naccording to certain classifications, the broadest of which is that\ninto external and internal, object and subject. The abstractions Matter\nand Mind once formed and fixed in representative symbols, are easily\naccredited as two different Reels. But the separation is ideal, and\nis really a distinction of Aspects. We know ourselves as Body-Mind;\nwe do not know ourselves as Body _and_ Mind, if by that be meant two\ncoexistent independent Existents; and the illusion by which the two\nAspects appear as two Reals may be made intelligible by the analysis\nof any ordinary proposition. For example, when we say \u201cthis fruit\nis sweet,\u201d we express facts of Feeling--actual or anticipated--in\nabstract terms. The concrete facts are these: a colored feeling, a\nsolid feeling, a sweet feeling, etc., have been associated together,\nand the colored, solid, sweet group is symbolized in the abstract\nterm \u201cfruit\u201d But the color, solidity, and sweetness are also abstract\nterms, representing feelings associated in other groups, so that we\nfind \u201cfruit\u201d which has no \u201csweetness\u201d; and \u201csweetness\u201d in other things\nbesides \u201cfruits.\u201d Having thus separated ideally the \u201csweetness\u201d from\nthe \u201cfruit\u201d--which in the concrete sweet-fruit is not permissible--we\neasily come to imagine a real distinction. This is the case with the\nconcrete living organism when we cease to consider it in its concrete\nreality, and fix our attention on its abstract terms--Body and Mind. We\nthen think of Body apart from Mind, and believe in them as two Reals,\nthough neither exists apart.\n\nThere is no state of consciousness in which object and subject are\nnot indissolubly combined. There is no physical process which is\nnot indissolubly bound up with the psychical modes of apprehending\nit. Every idea is either an image or a symbol--it has therefore\nobjective reference, a material aspect. Every object is a synthesis\nof feelings--it has therefore subjective reference, a material\naspect. Thus while all the evidence points to the identity of Object\nand Subject, there is ample evidence for the logical necessity of\ntheir ideal separation as Aspects. This I have explained as a case\nof the general principle which determines all distinctions--namely,\nthe diversity in the modes of production of the products,\nwhich--subjectively--is diversity in the modes of apprehending them.\nThe optico-tactical experiences are markedly different from the other\nexperiences, as being more directly referred to the Not-Self which\nresists; and because these lend themselves to ideal constructions by\nmeans of images and symbols, it is these experiences into which we\ntranslate all the others when we come to explain them and assign their\nconditions. For--and this is the central position of our argument--all\ninterpretation consists in translating one set of feelings in the terms\nof another set. We condense sets of feelings in abstract symbols; to\n_understand_ these we must reduce them to their concrete significates.\nThey are signs; we must show what they are signs of.\n\nNow the symbols Object and Subject are the most abstract we can employ.\nBecause they are universal, they represent what cannot in reality be\ndivorced. We can, indeed, ideally separate ourselves from the Cosmos;\nin the same way we can ideally separate our inner Self or Soul from our\nouter Self or Body; and again our Soul from its sentient states, our\nBody from its physical changes. But not so in reality. The separation\nis a logical artifice, and a logical necessity for Science.\n\nThe necessity will be obvious to any one who reflects how the ideal\nconstructions of Science demand precision and integrity of terms. The\nproblem of Automatism brings this very clearly into view. The question\nis, Can we translate all psychological phenomena in mechanical terms?\nIf we _can_, we ought; because these terms have the immense advantage\nof being _exact_, dealing as they do with quantitative relations. But\nmy belief is that we cannot--nay, that we cannot even translate them\nall into physiological terms. The distinction between quantitative and\nqualitative knowledge (p. 354) is a barrier against the mechanical\ninterpretation. Physiology is a classificatory science, not a science\nof measurement. Nor can the laws of Mind be deduced from physiological\nprocesses, unless supplemented by and interpreted by psychical\nconditions individual and social.\n\n\n\n\nCHAPTER IV.\n\nCONSCIOUSNESS AND UNCONSCIOUSNESS.[211]\n\n\n48. Science demands precision of terms; and in this sense Condillac\nwas justified in defining it, \u201c_une langue bien faite_.\u201d The sciences\nof Measurement are exact because of the precision of their terms, and\nare powerful because of their exactness. The sciences of Classification\ncannot aspire to this precision, and therefore, although capable of\nattaining to a fuller knowledge of phenomena than can be reached\nby their rivals, this advantage of a wider range is accompanied by\nthe disadvantage of a less perfect exposition of results. While\nphysicists and chemists have only to settle the significance of the\nfacts observed, biologists and social theorists have over and above\nthis to settle the significance of the terms they employ in expressing\nthe facts observed. Hence more than half their disputes are at bottom\nverbal.\n\nThis is markedly the case in the question of Automatism. One man\ndeclares that animals are automata; another that they are conscious\nautomata; and while it is quite possible to hold these views and not\npractically be in disagreement with the views of ordinary men, or\nindeed with the views of spiritualist and materialist philosophers,\nwe can never be sure that the advocates of Automatism do not mean\nwhat they are generally understood to mean. If a man says that by an\nautomaton he does not here mean a machine, such as a steam-engine or\na watch, but a vital mechanism which has its parts so adjusted that\nits actions resemble those of a machine; and if he adds that this\nautomaton is also conscious of some of its actions, though unconscious\nof others, we can only object to his using terms which have misleading\nconnotations. If he mean by \u201cconscious automata,\u201d that animals are\nmechanisms moved on \u201cpurely mechanical principles,\u201d their consciousness\nhaving nothing whatever to do with the production of their actions,\nthen indeed our objection is not only to his use of terms, but to his\ninterpretation of the facts.\n\n49. The questions of fact are two: Are animal mechanisms rightfully\nclassed beside machines? and, Is consciousness a coefficient in the\nactions of animal mechanism? The first has already been answered; the\nsecond demands a preliminary settlement of the terms \u201cconscious,\u201d\n\u201cunconscious,\u201d \u201cvoluntary,\u201d and \u201cinvoluntary.\u201d The aim of Physiology\nis to ascertain the particular combinations of the elementary parts\ninvolved in each particular function--in a word, the mechanism of\norganic phenomena; and the modern Reflex Theory is an attempt to\nexplain this mechanism on purely mechanical principles, without the\nco-operation of other principles, especially those of Sensation and\nVolition. It is greatly aided by the ambiguity of current terms. We are\naccustomed to speak of certain actions as being performed unconsciously\nor involuntarily. We are also accustomed to say that Consciousness\nis necessary to transform an impression into a sensation, and that\nVolition is the equivalent of conscious effort. When, therefore,\nunconscious and involuntary actions are recorded, they seem to be\nactions of an insentient mechanism. The Reflex Theory once admitted, a\nrigorous logic could not fail to extend it to all animal actions.\n\n50. I reject the Reflex Theory, on grounds hereafter to be urged,\nbut at present call attention to the great ambiguity in the terms\n\u201cconscious\u201d and \u201cunconscious.\u201d In one sense no definition of\nConsciousness can be satisfactory, since it designates an ultimate\nfact, which cannot therefore be made more intelligible than it is\nalready. In another sense no definition is needed, since every one\nknows what is meant by saying, \u201cI am conscious of such a change,\nor such a movement.\u201d It is here the equivalent of Feeling. To be\nconscious of a change, is to feel a change. If we desire to express\nit in physiological terms, we must define Consciousness--\u201ca function\nof the organism\u201d; and this definition we shall find eminently useful,\nbecause the organism being a vital mechanism, and the integrity of that\nmechanism being necessary for the integrity of the function, while\nevery variation of the mechanism will bring a corresponding variation\nof the function, we shall have an objective guide and standard in\nour inquiries. Organisms greatly differ in complexity, yet because\nthey also agree in the cardinal conditions of Vitality, among which\nSensibility is one, we conclude that they all have Feeling; but the\nFeeling of the one will differ from that of another, according to the\ncomplexity of the sentient mechanism in each. The perfection of this\nmechanism lies in the co-ordination of its parts, and the consensus of\nits sentient activities; any disturbance of that consensus must cause\na modification in the total consciousness; and when the disturbance\nis profound the modification is marked by such terms as \u201cinsanity,\u201d\n\u201closs of consciousness,\u201d \u201cinsensibility.\u201d These terms do not imply\nthat the sentient organs have lost their Sensibility, but only that\nthe disturbed mechanism has no longer its normal consensus, no longer\nits normal state of Consciousness. Each organ is active in its own\nway so long as its own mechanism is preserved; but the united action\nof the organs having been disturbed, their _resultant_ function has\nbeen altered. Hence in a fit of Epilepsy there is a complete absence\nof some normal reactions, with exaggeration of others. In a state of\nComa there is no spontaneity--none of the manifold adaptations of the\norganism to fluctuating excitations, external and internal, observable\nin the normal state. The organism still manifests Sensibility--but\nthis is so unlike the manifestations when its mechanism is\nundisturbed (and necessarily so since the Sensibility varies with\nthe mechanism) that it is no longer called by the same name. In the\nnormal organism Sensibility means Feeling, or Consciousness; but in\nthe abnormal organism there is said to be a \u201closs of Consciousness.\u201d\nWhat the physiologist or the physician means by the phrase \u201closs of\nConsciousness\u201d is intelligible, and for his purposes unobjectionable.\nHe observes many organic processes going on undisturbed--the\nunconscious patient breathes, secretes, moves his limbs, etc. These\nprocesses are referred to the parts of the mechanism which are not\ndisturbed; they are obviously independent of that adjustment of the\nmechanism which by its _consensus_ has the special resultant named\nConsciousness; he therefore concludes that these, and many other\norganic processes, which are neither accompanied nor followed by\n_discriminated_ feelings, are the direct consequences of the stimulated\nmechanism. He never hesitates to adopt the popular language, and say,\n\u201cWe sometimes act unconsciously, perceive unconsciously, and even think\nunconsciously, all by the simple reflex of the mechanism.\u201d\n\nNow observe the opening for error in this language. The actions are\nsaid to go on unconsciously, and, because unconsciously, as pure\nreflexes, which are then assigned to an insentient mechanism, and\nlikened to the actions of machines. But, as I hope hereafter to make\nevident, the reflex mechanism necessarily involves Sensibility; and\ntherefore reflex actions may be unaccompanied by Consciousness--in\none meaning of that term--without ceasing to be sentient, the feelings\nare operative, although not discriminated. On the other hand, there is\nanother and very general meaning of the term Consciousness, which is\nthe equivalent of Sentience.\n\n51. In discussing Automatism, or the Reflex Theory, it is absolutely\nnecessary that we should first settle the meaning we assign to the\nterm Consciousness. The laxity with which the term is used may be seen\nin the enumeration occupying six pages of Professor Bain\u2019s account of\nthe various meanings. Psychology is often said to be \u201cthe science of\nthe facts of Consciousness\u201d; and the Brain is often assigned as \u201cthe\norgan of Consciousness.\u201d Yet there are many mental processes, and many\ncerebral processes, which are declared to be unconscious. Obviously if\nConsciousness is the function of the Brain, there can be no cerebral\nactivity which is unconscious; just as there can be no activity of the\nlungs which is not respiratory. Usage therefore points to a general\nand a special sense of the term. The general usage identifies it\nwith Sensibility, in its subjective aspect as Sentience, including\nall psychical states, both those classed under Sensation, and those\nunder Thought. These states are the \u201cfacts of consciousness\u201d with\nwhich Psychology is occupied. In the special usage it is distinguished\nfrom all other psychical states by a peculiar reflected feeling of\nAttention, whereby we not only _have_ a sensation, but also _feel_ that\nwe have it; we not only think, but are conscious that we are thinking;\nnot only act, but are conscious of what we do. It is this which Kant\nindicates when he defines it \u201cthe subjective form accompanying all our\nconceptions (_Begriffe_)\u201d; and Jessen when he defines it \u201cthe internal\nknowing of our knowing, an in itself reflected knowing.\u201d[212]\n\n52. We shall often have to recur to this general and this special\nmeaning, both of which are too firmly rooted for any successful attempt\nto displace them. The fact that some organic processes and some\nmental processes take place now consciously and now unconsciously,\ni.\u00a0e. now with the feeling of reflected attention, and now with no\nsuch feeling, assuredly demands a corresponding expression; nor, in\nspite of inevitable ambiguities, is there ground for regretting that\nthe expression chosen should be only an extension of the expression\nalready adopted for all other states of Sentience. A sentient or\nconscious state can only be a state of the sentient organism, itself\nthe unity of many organs, each having its Sensibility. There is\nmore or less consensus, but there is no introduction of a new agent\nwithin the organism, converting what was physical impression into\nmental reaction. From first to last there has been nothing but\nneural processes, and combinations of such processes--which, viewed\nsubjectively, are sentient processes. Thus the gradations of sensitive\nreaction are Sentience, Consentience, and Consciousness, which are\nrepresented in the Logic of Feeling and the Logic of Signs. The\nfamiliar term Conscience will then represent the Logic of Conduct.\nThus understood, we may say that a man sometimes acts unconsciously,\nor thinks unconsciously, although his action and thought are ruled\nby Consentience, as he sometimes acts and thinks unconscientiously,\nalthough he is not without obedience to Conscience on other occasions.\nThe feeling which determines an action is _operative_, although it\nmay not be _discriminated_ from simultaneous feelings. When this\nis the case, we say the feeling is unconscious; but this no more\nmeans that it is a purely physical process taking place outside the\nsphere of Sentience, than the immoral conduct of a man would be said\nto be mechanical, and not the conduct of a moral agent. There is\nundoubtedly a marked distinction expressed in the terms Consciousness\nand Unconsciousness, but it is not that of contrasts such as Mental\nand Physical, it is that of grades such as Light and Darkness. Just\nas Darkness is a positive optical sensation very different from mere\nprivation--just as it replaces the sensation of Light, blends with\nit, struggles with it, and in all respects differs from the _absence_\nof all optical sensibility in the skin; so Unconsciousness struggles\nwith, blends with, and replaces Consciousness in the organism, and is\na positive state of the sentient organism, not to be confounded with a\nmere negation of Sentience; above all, not to be relegated to merely\nmechanical processes.\n\n52 _a_. Remember that, strictly speaking, Consciousness is a\npsychological not a physiological term, and is only used in Physiology\non the assumption that it is the subjective _equivalent_ of an\nobjective process. To avoid the equivoque of \u201cunconscious sensation,\u201d\nwe may substitute the term \u201cunconscious neural process\u201d; and as all\nneural processes imply Sensibility, which in the subjective aspect is\nSentience, we say that Sentience has various modes and degrees--such\nas Perception, Ideation, Emotion, Volition, which may be conscious,\nsub-conscious, or unconscious. When Leibnitz referred to the fact of\n\u201cobscure ideas,\u201d and modern writers expressed this fact as \u201cunconscious\ncerebration,\u201d the first phrase did not imply a process that was other\nthan mental, the second phrase did not imply a process that was other\nthan physiological: both indicated a mode of the process known as\nConsciousness under other modes. There are different neural elements\ngrouped in Ideation and Emotion; there are different neural elements\ngrouped in Consciousness, Sub-consciousness, and Unconsciousness; but\none tissue with one property is active in all.\n\n53. The nervous organism is affected as a whole by every affection\nof its constituent parts. Every excitation, instead of terminating\nwith itself--as is the case in most physical processes--or with the\nmotor impulse it excites, is propagated throughout the continuous\ntissue, and thus sends a _thrill_ throughout the organism. The wave\nof excitation in passing onwards beats against variously grouped\nelements--temporary and permanent centres--disturbing their balance\nmore or less, and liberating the energy of some, increasing the tension\nof others, necessarily affecting all. Those groups which have their\nenergy liberated set up processes that are either _discriminated_\nas sensations, or are blended with the general stream, according\nto their _relative_ energy in the consensus. Thus the impulse on\nreaching the centres for the heart, lungs, legs, and tail excites\nthe innervation of these organs; but as these are only parts of the\norganism, and as all the parts enter the consensus, and Consciousness\nis the varying resultant of this ever-varying consensus, the\nthrill which any particular stimulus excites will be unconscious,\nsub-conscious, or conscious, in proportion to the extent of the\n_irradiated_ disturbance, which will depend on the statical conditions\nof the centres at the moment. A sound sends a thrill which excites\nemotion, causes the heart to beat faster, the muscles to quiver, the\nskin-glands to pour forth their secretion; yet this same sound heard\nby another man, or the same man under other conditions, physical or\nhistorical, merely sends a faint thrill, just vivid enough to detach\nitself as a sensation from the other simultaneous excitations; and\nthe same sound may excite a thrill which is so faint and fugitive as\nto pass unconsciously. Physiological and psychological inductions\nassure us that these are only differences of degree. The same kind\nof physiological effect accompanies the conscious and unconscious\nstate. Every sensory impression, no matter whether discriminated or\nnot, affects the circulation and develops heat. The blood-vessels of\nthe part impressed expand, vessels elsewhere contract--a change in\nthe blood pressure has been effected, which of course implies that\nthe whole organism has been affected. Delicate instruments show that\nat the time a sensation is produced the temperature of the brain is\nraised. The same is true of ideation. Mosso has invented a method of\nregistering the effect of thought on the circulation. He finds ideation\naccompanied by a contraction of the peripheral vessels proportionate\nto the degree of intellectual effort. A young man translating Greek\nshowed greater contraction than when he was translating Latin. During\nsound sleep--when we are said to be unconscious--sudden noises\nalways cause contraction of the peripheral vessels. Psychological\nobservation assures us that the conscious and unconscious states\nwere both consentient, and were both operative in the same degree.\nThe absorbed thinker threads his way through crowded streets, and is\nsub-conscious and unconscious of the various sights, sounds, touches,\nand muscular movements which make up so large a portion of his sentient\nexcitation at the time; yet he deftly avoids obstacles, hears the\nsound of a hurried step behind him, recognizes an interesting object\ndirectly it presents itself, and can even recall in Memory many of the\nuninteresting objects which he passed in sub-conscious and unconscious\nindifference.\n\n54. On all grounds, therefore, we must say that between conscious,\nsub-conscious, and unconscious states the difference is only of\ndegree of complication in the neural processes, which by relative\npreponderance in the consensus determine a relative discrimination. We\ncan only discriminate one thrill at a time; but the neural excitations\nsimultaneously pressing towards a discharge are many; and the\nconditions which determine now this, and now the other excitation to\npredominate by its differential pressure, are far beyond any mechanical\nestimate. I mention this because the advocates of the Reflex Theory\nmaintain that the neural processes are the same whether a sensation be\nproduced or not; and that since the same actions follow the external\nstimulation whether sensation be produced or not, this proves the\nactions to be purely mechanical. I reply, the neural processes are\n_not_ the same throughout in the two cases--otherwise the effects would\nbe the same. You might as well say, \u201cSince the explosion of the gun\nis the same, whether shotted or not, a blank cartridge will kill\u201d;\nbut if you tell me that your gun killed the bird, I declare that the\ncartridge was _not_ a blank one. Whether the explosion of the gun\n_also_ produced terror in one bystander, curiosity in a second, and\nattracted no notice from a third, will be altogether another matter.\nIn like manner the sensory impression which determines a movement may\nor may not be accompanied or followed by _other_ sentient states; the\nfact of such movement is evidence of its sentient antecedent; and an\nexternal stimulus that will produce _this_ neural process, and this\nconsequent movement, must produce a feeling, although not necessarily a\ndiscriminated sensation. Now since, for discrimination, _other_ neural\nprocesses must co-operate, we cannot say that in the two cases _all_\nthe neural processes have been the same throughout; nor because of this\ndifference can we say that the process of the undiscriminated sensation\nis a mechanical, not a sentient process. In the next problem this point\nwill be argued more fully.\n\n55. The need of recognizing Consciousness and Consentience as degrees\nof energy and complexity in sentient states is apparent when we\nconsider animal phenomena. Has a bee consciousness? Has a snail\nvolition? or are they both insentient mechanisms? All inductions\nwarrant the assertion that a bee has thrills propagated throughout its\norganism by the agency of its nerves; and that some of these thrills\nare of the kind called sensations--even discriminated sensations.\nNevertheless we may reasonably doubt whether the bee has sentient\nstates resembling otherwise than remotely the sensations, emotions,\nand thoughts which constitute human Consciousness, either in the\ngeneral or the special sense of that term. The bee feels and reacts on\nfeelings; but its feelings cannot closely resemble our own, because\nthe conditions in the two cases are different. The bee may even be\nsaid to think (in so far as Thought means logical combination of\nfeelings), for it appears to form Judgments in the sphere of the Logic\nof Feeling--\u03c4\u03bf \u03bd\u03bf\u03b7\u03c4\u03b9\u03ba\u1f78\u03bd; although incapable of the Logic of Signs--\u03c4\u03bf\n\u03b4\u03b9\u03b1\u03bd\u03bf\u03b7\u03c4\u03b9\u03ba\u03bf\u03bd. We should therefore say the bee has Consentience, but\nnot Consciousness--unless we accept Consciousness in its _general_\nsignification as the equivalent of Sentience. The organism of the bee\ndiffers from that of a man, as a mud hut from a marble palace. But\nsince underlying these differences there are fundamental resemblances,\nthe functions of the two will be fundamentally alike. Both have the\nfunction of Sentience; as mud hut and palace have both the office of\nsheltering.\n\n56. The question of Volition will occupy us in the next chapter.\nRestricting ourselves here to that of Consciousness, and recalling\nthe distinction of the two meanings of the term, we now approach\nthe question of Unconsciousness. Are we to understand this term as\ndesignating a purely physical state in contrast to the purely mental\nstate of Consciousness; or only as designating a difference of degree?\nThis is like asking whether Light and Darkness are both optical\nfeelings, or one an optical feeling and the other a physical process?\nOn the Reflex Theory, no sooner does a vital and mental process pass\nfrom the daylight of Consciousness, or twilight of Sub-consciousness,\ninto the darkness of Unconsciousness, than the whole order of phenomena\nis abruptly changed, they cease to be vital, mental, and lapse into\nphysical, mechanical processes. The grounds of this conclusion are,\nfirst, the unpsychological assumption that the unconscious state is\nout of the sphere of Sentience; and secondly, the unphysiological\nassumption that the Brain is the only portion of the nervous system\nwhich has the property of Sensibility. Restate the conclusion in\ndifferent terms and its fallacy emerges: \u201corganic processes suddenly\ncease to be organic, and become purely physical by a slight change\nin their _relative_ position in the consensus; the organic process\nwhich was a conscious sensation a moment ago, when its energy was not\nbalanced by some other process, suddenly falls from its place in the\ngroup of organic phenomena--sentient phenomena--to sink into the group\nof inorganic phenomena now that its energy is balanced.\u201d Consider the\nparallel case of Motion and Rest in the objective sphere. They are two\nfunctions of the co-operant forces, one dynamic, the other static;\nalthough markedly distinguishable as functions, we know that they are\nsimply the co-operant forces now unbalanced and now balanced; what\nwe call Rest is also a product of moving forces, each of which is\noperant, and will issue in a definite resultant when its counter-force\nis removed. Motion and Rest are correlatives, and both belong to the\nsphere of Kinetics. In like manner Consciousness and Unconsciousness\nare correlatives, both belonging to the sphere of Sentience.[213] Every\none of the unconscious processes is operant, changes the general state\nof the organism, and is capable of at once issuing in a discriminated\nsensation when the force which balances it is disturbed. I was\nunconscious of the scratch of my pen in writing the last sentence, but\nI am distinctly conscious of every scratch in writing this one. Then,\nas now, the scratching sound sent a faint thrill through my organism,\nbut its relative intensity was too faint for discrimination; now that I\nhave redistributed the co-operant forces, by what is called an act of\nAttention, I hear distinctly every sound the pen produces.\n\n57. The inclusion of Sub-consciousness within the sentient sphere is\nobvious; the inclusion of Unconsciousness within that sphere may be\nmade so, when we consider its modes of production, and compare it\nwith the extra-sensible conception of molecules and atoms. The Matter\nwhich is sensible as masses, may be resolved into molecules, which lie\nbeyond the discrimination of sense; and these again into atoms, which\nare purely ideal conceptions; but because molecules are _proved_, and\natoms are _supposed_, to have material properties, and to conform to\nsensible canons of the objective world, we never hesitate to class them\nunder the head of Matter; nor do we imagine that in passing beyond the\ndiscrimination of Sense they lose their objective significance. They\nare still physical, not mental facts. So with Sentience: we may trace\nit through infinite gradations from Consciousness to Sub-consciousness,\ntill it fades away in Unconsciousness; but from first to last the\nprocesses have been those of a sentient organism; and by this are\nbroadly distinguished from all processes in anorganisms. The movement\nof a limb has quite different modes of production from the movement of\na wheel; and among its modes must be included those of Sensibility,\na peculiarly vital property. Oxidation may be slow or rapid,\nmanifesting itself as combustion, heat, or flame, but it is always\noxidation--always a special chemical phenomenon. And so the neural\nprocess of Sentience, whether conscious, sub-conscious, or unconscious,\nis always a state of the sentient organism. If a material process does\nnot change its character, and become spiritual, on passing beyond the\nrange of sensible appreciation, why should a psychical process become\nmaterial on passing beyond the range of discrimination? If we admit\nmolecules as physical units, sentient tremors are psychical units.\nThe extra-sensible molecules have indeed their subjective aspect,\nand only enter perception through the \u201cgreeting of the spirit.\u201d The\nsentient tremors have also their objective aspect, and cannot come\ninto existence without the neural tremors, which are their physical\nconditions.\n\n58. It is only by holding fast to such a conception that we can escape\nthe many difficulties and contradictions presented by unconscious\nphenomena, and explain many physiological and psychological processes.\nDescartes--followed by many philosophers--identified Consciousness\nwith Thought. To this day we constantly hear that to have a sensation,\nand to be conscious of it, is one and the same state; which is only\nadmissible on the understanding that Consciousness means Sentience,\nand Sentience the activity of the nervous system viewed subjectively.\nLeibnitz pointed out that we have many psychical states which are\nunconscious states--to have an idea and be conscious of it, are, he\nsaid, not one but two states. The Consciousness by Descartes erected\ninto an essential condition of Thought, was by Leibnitz reduced to an\naccompaniment which not only may be absent, but in the vast majority\nof cases is absent. The teaching of most modern psychologists is\nthat Consciousness forms but a small item in the total of psychical\nprocesses. Unconscious sensations, ideas, and judgments are made to\nplay a great part in their explanations. It is very certain that in\nevery conscious volition--every act that is so characterized--the\nlarger part of it is quite unconscious. It is equally certain that\nin every perception there are unconscious processes of reproduction\nand inference--there is much that is _implicit_, some of which cannot\nbe made explicit--a \u201cmiddle distance\u201d of sub-consciousness, and a\n\u201cbackground\u201d of unconsciousness. But, throughout, the processes are\nthose of Sentience.\n\n59. Unconsciousness is by some writers called _latent_ Consciousness.\nExperiences which are no longer manifested are said to be stored up in\nMemory, remaining in the Soul\u2019s picture-gallery, visible directly the\nshutters are opened. We are not conscious of these feelings, yet they\nexist as latent feelings, and become salient through association. As a\nmetaphorical expression of the familiar facts of Memory this may pass;\nbut it has been converted from a metaphor into an hypothesis, and we\nare supposed to _have_ feelings and ideas, when in fact we have nothing\nmore than a modified _disposition_ of the organism--temporary or\npermanent--which when stimulated will respond in this modified manner.\nThe modification of the organism when permanent becomes hereditary; and\nits response is then called an instinctive or automatic action. And as\nactions pass by degrees from conscious and voluntary into sub-conscious\nand sub-voluntary, and finally into unconscious and involuntary, we\ncall them volitional, secondarily automatic, and automatic. If any one\nlikes to say the last are due to latent consciousness, I shall not\nobject. I only point to the fact that the differences here specified\nare simply differences of degree--all the actions are those of the\nsentient organism.\n\n60. Picture to yourself this sentient organism incessantly stimulated\nfrom without and from within, and adjusting itself in response to such\nstimulations. In the blending of stimulations, modifying and arresting\neach other, there is a fluctuating \u201ccomposition of forces,\u201d with\never-varying resultants. Besides the stream of direct stimulations,\nthere is a wider stream of indirect or reproduced stimulations.\nTogether with the present sensation there is always a more or less\ncomplex group of revived sensations, the one group of neural tremors\nbeing organically stimulated by the other. An isolated excitation is\nimpossible in a continuous nervous tissue; an isolated feeling is\nimpossible in the consensus or unity of the sentient organism. The term\nSoul is the personification of this complex of present and revived\nfeelings, and is the substratum of Consciousness (in the general\nsense), all the particular feelings being its _states_. To repeat an\nillustration used in my first volume, we may compare Consciousness to\na mass of stationary waves. If the surface of a lake be set in motion\neach wave diffuses itself over the whole surface, and finally reaches\nthe shores, whence it is reflected back towards the centre of the lake.\nThis reflected wave is met by the fresh incoming waves, there is a\nblending of the waves, and their product is a pattern on the surface.\nThis pattern of stationary waves is a fluctuating pattern, because of\nthe incessant arrival of fresh waves, incoming and reflected. Whenever\na fresh stream enters the lake (i.\u00a0e. a new sensation is excited from\nwithout), its waves will at first pass over the pattern, neither\ndisturbing it nor being disturbed by it; but after reaching the shore\nthe waves will be reflected back towards the centre, and there will\nmore or less modify the pattern.\n\n\n\n\nCHAPTER V.\n\nVOLUNTARY AND INVOLUNTARY ACTIONS.\n\n\n61. Much of what has been said in the preceding chapter respecting\nthe passive side of the organism is equally applicable to the active\nside. Our actions are classed as voluntary and involuntary mainly in\nreference to their being consciously or unconsciously performed; but\nnot wholly so, for there are many involuntary actions of which we are\ndistinctly conscious, and many voluntary actions of which we are at\ntimes sub-conscious and unconscious. I do not propose here to open the\nlong and arduous discussion as to what constitutes Volition, my present\npurpose being simply that of fixing the meaning of terms, so that the\nquestion of Automatism may not be complicated by their ambiguities.\n\u201cVoluntary\u201d and \u201cinvoluntary\u201d are, like \u201cconscious\u201d and \u201cunconscious,\u201d\ncorrelative terms; but commonly, instead of being understood as\nindicating differences of degree in phenomena of the same order, they\nare supposed to indicate differences of kind--a new agent, the Will,\nbeing understood in the one case to direct the Mechanism which suffices\nwithout direction in the other.\n\n62. This interpretation is unphysiological and unpsychological,\nsince it overlooks the fact that both voluntary and involuntary\nactions belong to the same _order_ of phenomena, i.\u00a0e. those of the\nsentient organism. Both involve the same _efficient_ cause, i.\u00a0e.\nco-operant conditions. We draw a line of demarcation between the two\nabstractions--as between all abstractions--but the concrete processes\nthey symbolize have no such demarcation. Just as the thought which at\none moment passes unconsciously, at another consciously, is in itself\nthe same thought, and the same neural process; so the action which at\none moment is voluntary, and at another involuntary, is itself the same\naction, performed by the same mechanism. The incitation which precedes,\nand the feeling which accompanies the action, belong to the accessory\nmechanisms, and may be replaced by other incitations and other\nfeelings; as the fall of an apple is the same event, involving the same\nconditions, i.\u00a0e. efficient cause, whether the _occasional_ cause be a\ngust of wind or the gardener\u2019s scissors, and whether the fall be seen\nand heard or not. I may utter words intentionally and consciously, and\nI may utter the same words automatically, unconsciously; I may wink\nvoluntarily, and wink involuntarily. There are terms to express these\ndifferences; but they do not express a difference in the efficient\nagencies.\n\n63. Many writers seem to think that the involuntary actions belong\nto the physical mechanical order, because they are not stimulated by\ncerebral incitations, and cannot be regulated or controlled by such\nincitations--or as the psychologists would say, because Consciousness\nin the form of Will is no agent prompting and regulating such actions.\nBut I think this untenable. The actions cannot belong to the mechanical\norder so long as they are the actions of a vital mechanism, and so long\nas we admit the broad distinction between organisms and anorganisms.\nWhether they have the special character of Consciousness or not,\nthey have the general character of sentient actions, being those\nof a sentient mechanism. And this becomes the more evident when we\nconsider the gradations of the phenomena. Many, if not all, of those\nactions which are classed under the involuntary were originally of\nthe voluntary class--either in the individual or his ancestors; but\nhaving become permanently organized dispositions--the pathways of\nstimulation and reaction having been definitely established--they have\nlost that volitional element (of hesitation and choice) which implies\nregulation and control. But even here a slight change in the habitual\nconditions will introduce a disturbance in the process which may\nawaken Consciousness, and the sense of effort, sometimes even causing\ncontrol. An instinctive or an automatic action may be thus changed,\nor arrested. Take as an example one of the unequivocally automatic\nactions, that of Breathing. It is called automatic because, like the\nactions of an automaton, it is performed by a definitely constructed\nmechanism, always working in the same way when stimulated and left to\nitself. There must of course be a sense of effort in every impulse\nwhich has resistance to overcome, organs to be moved; but the mechanism\nof Breathing is so delicately adjusted, that the sense of effort is\nreduced to a minimum, and we are unconscious of it, or sub-conscious\nof it. Nevertheless, without altering the rate or amplitude of the\ninspirations and expirations, we become distinctly conscious of them,\nand, moreover, within certain limits we can control them, so that the\nBreathing passes from the involuntary to the voluntary class.\n\n64. Pass on to other examples. What action can be more involuntary than\nthe rhythmic movements of the heart and the contractions of the iris?\nCompared with the actions of the tongue or limbs, these seem riveted\nby an iron necessity, freed from all consciousness and control. Yet\nthe movements of the heart are not only stimulated by sensations and\nthoughts, they are also capable of being felt; and the movements both\nof heart and iris are not wholly removed from our control. That we do\nnot habitually control (that is, _interfere_ with) the action of the\nheart, the contraction of the iris, or the activity of a gland, is\ntrue; it is on this account that such actions are called involuntary;\nthey obey the immediate stimulus. But it is an error to assert that\nthese actions _cannot_ be controlled, that they are altogether beyond\nthe interference of other centres, and cannot by any effort of ours\nbe modified. It is an error to suppose these actions are essentially\ndistinguished from the voluntary movement of the hands. We have\nacquired a power of definite direction in the movements of the hands,\nwhich renders them obedient to our will; but this acquisition has been\nof slow laborious growth. If we were asked to use our toes as we use\nour fingers--to grasp, paint, sew, or write with them, we should find\nit not less impossible to control the movements of the toes in these\ndirections, than to contract the iris, or cause a burst of perspiration\nto break forth. Certain movements of the toes are possible to us; but\nunless the loss of our fingers has made it necessary that we should\nuse our toes in complicated and slowly acquired movements, we can do\nno more with them than the young infant can do with his fingers. Yet\nmen and women have written, sewed, and painted with their toes. All\nthat is requisite is that certain links should be established between\nsensations and movements; by continual practice these links _are_\nestablished; and what is impossible to the majority of men, becomes\neasy to the individual who has acquired this power. This same power\ncan be acquired over what are called the organic actions; nevertheless\nthe habitual needs of life do not _tend_ towards such acquisition,\nand without some strong current setting in that direction, or some\npeculiarity of organization rendering it easy, it is never acquired.\nIn ordinary circumstances the number of those who can write with their\ntoes is extremely rare, the urgent necessity which would create such a\npower being rare; and rare also are the examples of those who have any\ncontrol over the movement of the iris, or the action of a gland; but\nboth rarities exist.\n\nIt would be difficult to choose a more striking example of reflex\naction than the contraction of the iris of the eye under the stimulus\nof light;[214] and to ordinary men, having no link established which\nwould guide them, it is utterly impossible to close the iris by any\neffort. It would be not less impossible to the hungry child to get\non the chair and reach the food on the table, until that child had\n_learned_ how to do so. Yet there are men who have learned how to\ncontract the iris. The celebrated Fontana had this power; which is\npossessed also by a medical man now living at Kilmarnock--Dr. Paxton--a\nfact authenticated by no less a person than Dr. Allen Thomson.[215] Dr.\nPaxton can contract or expand the iris at will, without changing the\nposition of his eye, and without an effort of adaptation to distance.\n\nTo move the ears is impossible to most men. Yet some do it with ease,\nand all could learn to do it. Some men have learned to \u201cruminate\u201d their\nfood; others to vomit with ease; and some are said to have the power of\nperspiring at will.[216] Now, if once we recognize a link of sensation\nand motion, we recognize a possible source of control; and if the\ndaily needs of life were such that to fulfil some purpose the action\nof the heart required control, we should learn to control it. Some\nmen have, without such needs, learned how to control it. The eminent\nphysiologist, E. F. Weber of Leipzig, found that he could completely\ncheck the beating of his heart. By suspending his breath and violently\ncontracting his chest, he could retard the pulsations; and after\nthree or five beats, unaccompanied by any of the usual sounds, it was\ncompletely still. On one occasion he carried the experiment too far,\nand fell into a syncope. Cheyne, in the last century, recorded the case\nof a patient of his own who could at will suspend the beating of his\npulse, and always fainted when he did so.\n\n65. It thus appears that even the actions which most distinctly bear\nthe character recognized as involuntary--uncontrollable--are only so\nbecause the ordinary processes of life furnish no necessity for their\ncontrol. We do not learn to control them, though we could do so, to\nsome extent; nor do we learn to control the motions of our ears,\nalthough we could do so. And while it appears that the involuntary\nactions can become voluntary, it is familiar to all that the voluntary\nactions tend, by constant repetition, to become involuntary. Thus\ninvoluntary actions, under certain limitations, may be controlled; on\nthe other hand, the voluntary are incapable of being controlled under\nthe urgency of direct stimulation. Both are reflexes.\n\nInasmuch as almost all actions are the products of stimulated\nnerve-centres, it is obvious that these actions are reflex--reflected\nfrom those centres. It matters not whether I wink because a sensation\nof dryness, or because an idea of danger, causes the eyelid to close:\nthe act is equally reflex. The nerve-centre which supplies the eyelid\nwith its nerve has been stimulated; the stimuli may be various, the\nact is uniform. At one time the stimulus is a sensation of dryness,\nat another an idea of danger, at another the idea of communicating\nby means of a wink with some one present; in each case the stimulus\nis reflected in a muscular contraction. Sensations excite other\nsensations; ideas excite other ideas; and one of these ideas may issue\nin an action of control. But the restraining power is limited, and\ncannot resist a certain degree of urgency in the original stimulus. I\ncan, for a time, restrain the act of winking, in spite of the sensation\nof dryness; but the reflex which sets going this restraining action\nwill only last a few seconds; after which, the urgency of the external\nstimulus is stronger than that of the reflex feeling--the sensation of\ndryness is more imperious than the idea of resistance--and the eyelid\ndrops.\n\nIf a knife be brought near the arm of a man who has little confidence\nin the friendly intentions of him that holds it, he shrinks, and the\nshrinking is \u201cinvoluntary,\u201d i.\u00a0e. in spite of his will. Let him have\nconfidence, and he does not shrink, even when the knife touches his\nskin. The idea of danger is not excited in the second case, or if\nexcited, is at once banished by another idea. Yet this very man, who\ncan thus repress the involuntary shrinking when the knife approaches\nhis arm, cannot repress the involuntary winking when the same friend\napproaches a finger to his eye. In vain he prepares himself to resist\nthat reflex action; in vain he resolves to resist the impulse; no\nsooner does the finger approach, than down flashes the eyelid. Many\nmen, and most women, would be equally unable to resist shrinking on the\napproach of a knife: the association of the idea of danger with the\nknife would bear down any previous resolution not to shrink. It is from\nthis cause that timorous women tremble at the approach of firearms. An\nassociation is established in their minds which no idea is powerful\nenough to loosen. You may assure them the gun is not loaded; \u201c_that_\nmakes very little difference,\u201d said a na\u00efve old lady to a friend of\nmine. They tremble, as the child trembles when he sees you put on the\nmask. These illustrations show that the urgency of any one idea may,\nlike the urgency of a sensation, bear down the resistance offered by\nsome other idea; as the previous illustrations showed that an idea\ncould restrain or control the action which a sensation or idea would\notherwise have produced. According to the doctrines current, the Will\nis said to be operative when an idea determines an action; and yet all\nwould agree that the winking which was involuntary when the idea of\ndanger determined it, was voluntary when the idea of communicating with\nan accomplice in some mystification determined it.\n\n66. There is no real and essential distinction between voluntary and\ninvoluntary actions. They all spring from Sensibility. They are all\ndetermined by feeling. It is convenient, for common purposes, to\ndesignate some actions as voluntary; but this is merely a convenience;\nno psychological nor physiological insight is gained by it; an analysis\nof the process discloses no element in a voluntary action which is\nnot to be found in an involuntary action--except in the origin or\ndegree of stimulation. In ordinary language it is convenient to mark a\ndistinction between my raising my arm because I will to raise it for\nsome definite purpose, and my raising it because a bee has stung me; it\nis convenient to say, \u201cI _will_ to write this letter,\u201d and \u201cthis letter\nis written against my will--I have no will in the matter.\u201d But Science\nis more exacting when it aims at being exact; and the philosopher,\nanalyzing these complex actions, will find that in each case certain\nmuscular groups have been set in action by different sensational or\nideational stimuli. The action itself is that of a neuro-muscular\nmechanism, which mechanism works in the same way, whatever be the\nsource of the original impulse. The stimulation may be incited\ndirectly from the periphery, or indirectly from a remote centre; and\nthe action may be arrested by a peripheral or central stimulation:\nthe reflex which ordinarily follows the excitation of a sensory nerve\nwill be modified, or arrested, if some other nerve be at the same time\nstimulated. (See Law of Arrest, _Prob._ II. \u00a7 190.)\n\n67. All actions are reflex, all are the operations of a mechanism,\nall are sentient, because the mechanism has Sensibility as its vital\nproperty. In thus preserving the integrity of the order of vital\nphenomena, and keeping them classified apart from physical and chemical\nphenomena, we by no means set aside the useful distinctions expressed\nin the terms voluntary and involuntary; any more than we set aside the\ndistinction of vertebrate and invertebrate when both are classed under\nAnimal, and separated from Plant, or Planet.\n\nThe mechanisms of the special Senses respond in special reactions;\nthe mechanisms of special actions have also their several responses.\nThe tail responds to stimulation with lateral movements, the chest\nwith inspiration and expiration, and so on. These responses are called\nautomatic, and have this in common with the actions of automata that\nthey are uniform, and do not need the co-operation of Consciousness,\nthough they do need the operation of Sensibility, and are thereby\ndistinguished from the actions of automata. The facial muscles, and\nthe limbs, also respond to stimulation in uniform ways, but owing to\nthe varieties of stimulation the actions are more variable, and have\nmore the character of volitional movements. With this greater freedom\nof possible action comes the eminently mental character of _choice_.\nIn the cerebral rehearsal of an act not yet performed--its mental\nprevision--as when we intend to do something, yet for the moment\narrest the act, so that there is only a nascent excitation of the\nmotor process, there is a peculiar state of Consciousness expressive\nof this state of the mechanism: we call the prevision a _motive_--and\nit becomes a _motor_ when the intention is realized, the nascent\nexcitation becomes an unchecked impulse. The abstract of all motives we\ncall Will. A motive is a volition in the sphere of the Intellect. In\nthe sphere of Emotion it is a motor. Hence we never speak of the Will\nof a mollusc, or the motives of an insect, only of their sensations and\nmotors. Yet it is obvious that the reflex in operation when a snail\nshrinks at the approach of an object is essentially similar to the\nreflex in operation when the baby shrinks, and this again is still more\nsimilar to that in operation when the boy shrinks: the boy has the idea\nof danger, which neither baby nor snail can have; the idea is a motive,\nwhich can be controlled by another idea; the baby and the snail can\nhave no such motive, no such control--are they therefore automata?\n\n68. If I see that a donkey has wandered into my garden, the motive\nwhich determines me to take a stick and with it drive the donkey\naway is a cerebral rehearsal of the effects which will follow my\nact. The sight of the donkey has roused disagreeable feelings,\nand these suggest possible means of alleviation; out of these\npossibilities--reproductions of former experiences--I choose one.\nBut if I seize the stick with which some one is threatening me, I do\nnot pause to choose, I snatch automatically without hesitation. Yet\nthis unreflecting automatic act is itself as truly volitional as my\nseizing the stick to drive away the donkey--it is the motor which has\nbeen organized in me by previous experiences--it is the consequence\nof an emotion, not of a deliberation; and it has not been determined\nby any clear prevision of consequences. Feeling inspires, and feeling\nguides my movements, so that if my snatch has missed the stick, I\nsnatch again, or duck under. This is the kind of Volition we ascribe\nto animals. It is a great part of our own. By insensible degrees, acts\nwhich originally were prompted by motives sink into the automatic\nclass prompted by motors. When an angry man snatches up a knife, doffs\nbystanders aside, and rushes on his enemy to stab him, he does not\ndistinctly prefigure the final result, he only obeys each motor, and\nis conscious of each step; but had he planned the murder he would have\nforeseen the end, and this prevision would have been the motive. The\nangry man is struck with horror at the sight of the bleeding corpse,\nand passionately declares he did not _mean_ to kill. Nor did he will\nthe consequences of his act, yet he certainly willed each separate\nstep--he recognized the knife, saw the bystanders, knew they would\ninterfere with him, willed to push them aside. He may be right in\ndeclaring that the act was involuntary; but assuredly it was not purely\nmechanical.\n\n69. Again, we are not conscious of the separate sensations which guide\nspeech or writing; we cannot properly be said to will the utterance\nof each tone, or the formation of each letter. Are these processes\nmechanical and not volitional? By no means. We know that they were\nlaboriously learned by long tentative efforts, each of which was\naccompanied by distinct consciousness. We also know that now when the\nmechanism is so easy in its adjustment as to suggest automatism, there\nneeds but a slight alteration in the conditions to make us distinctly\nconscious of the processes--the wrong word spoken, or one letter ill\nformed, suffices to arrest the easy working of the mechanism. A similar\nmechanism operates in thinking, which also lapses from the conscious\nand voluntary to the unconscious and involuntary state. The logical\nprocess of Judgment is as purely a reflex from one neural group to\nanother, as the physiological process of co-ordination. In ordinary\nthinking we are as little conscious of the particular steps--our\ninterest being concentrated on the result--as we are of the particular\nstages of an action. The adjustments of the mechanism of Reproduction\nand Association are _set_ going by a motive, and _kept_ going by\npsychological motors. And here--as in bodily actions--there is often\na conflict between motive and motors--between the foreseen result,\nand the available means of reaching it--the motors usually prevailing\nbecause they represent the active side of the mechanism. Thus when an\noculist wishes to examine a patient\u2019s eye, he does not tell him to give\na particular direction to his eye, knowing that the _motive_ to do so\nwill not suffice; instead of this he simply moves his own hand in the\ndesired direction, certain that the eye will by reflex irresistibly\nfollow it. Nay, there are sometimes such anomalies of innervation\nthat the eye, instead of obeying the motive, moves in a contrary\ndirection. Meschede mentions a patient whose movements were mostly of\nthis anomalous kind: when he willed to move the eyes to the right, they\nmoved to the left; when he willed to move them up, they moved down. It\nwas thus also with his hands and feet. Yet he was distinctly conscious\nthat his intention had been frustrated, and that he acted \u201cbecause he\ncould not help it.\u201d[217] How insensibly a motive sinks into a motor,\nthat is to say, a voluntary into an involuntary act, may be recognized\nin speech, writing, singing, walking, etc., and in the incessant\nmovements of the eye in fixing objects. Aubert has well remarked\nthat we only give definite movements to the eye when we wish to see\nan object distinctly. Whenever the indistinct vision suffices--as in\nwalking through the streets occupied in conversation or thought--we\nmake no such movements; but no sooner does any object excite our\nattention, than the effort to fix that object at once excites the\nnecessary reflex.[218]\n\n70. By the Will, then, we must understand the abstract generalized\nexpression of the impulses which determine actions, when those\nimpulses have an ideal origin; by Volition the still more generalized\nexpression of all impulses which determine actions. The one class is\nthat of _motives_ with ideal elements; the other that of _motors_ with\nsensational or emotional elements. But both are mental states, both\nare neural processes in a sentient organism; neither is mechanical,\nexcept in so far as all actions are expressible in mechanical terms.\nFor convenience we class actions as reflex, automatic, involuntary,\nunconscious, voluntary, and conscious. If we separate the reflex\nfrom the voluntary, we need not therefore dissociate the former from\nSensibility; and the reason why we ought not to separate it is that we\nknow it to be sense-guided from first to last, although the sensations\nmay escape discrimination. The feeling of Effort, which was formerly\nfelt when an action was performed, may have become so minimized\nthat it is too faint for more than a momentary consciousness, too\nevanescent for the memory to retain it; yet the feeling must always\nbe operant when its mechanism is in action. The ease with which the\nmechanism works does not change the adjustment of its elements, nor\nalter its character. The facile unobtrusive performance of a vital\nfunction does not change it from a vital to a mechanical act. Mr.\nSpencer seems to me to express himself ambiguously when he says:\n\u201cJust as any set of psychical changes originally displaying Memory,\nReason, and Feeling cease to be conscious, rational, and emotional\nas fast as they by repetition grow closely organized, so do they at\nthe same time pass beyond the sphere of Volition. Memory, Reason,\nFeeling, and Will disappear in proportion as psychical changes become\nautomatic\u201d[219]--for while it is perfectly true that we only call those\npsychical changes \u201cautomatic\u201d which have lost the special qualities\ncalled \u201cconscious, rational, and emotional,\u201d it is not less true that\nthey remain from first to last _psychical_ changes, and are thereby\ndistinguished from _physical_ changes. To suppose that they pass from\nthe psychical to the physical by frequent repetition would lead to the\nmonstrous conclusion that when a naturalist has by laborious study\nbecome so familiarized with the specific marks of an animal or plant\nthat he can recognize at a glance a particular species, or recognize\nfrom a single character the nature of the rest, the rapidity and\ncertainty of this judgment proves it to be a mechanical, not a mental\nact. The intuition with which a mathematician sees the solution of a\nproblem would then be a mechanical process, while the slow and bungling\nhesitation of the tyro in presence of the same problem would be a\nmental process: the perfection of the organism would thus result in its\ndegradation to the level of a machine!\n\nThe operations of the intellect may furnish us with an illustration.\nIdeas are symbols of sensations. The idea of a horse is an abstraction\neasily traceable to concrete sensations, yet as an abstraction is\nso different a state of feeling that we only identify it with its\nconcretes by a careful study of its stages of evolution, namely,\nsensation, image, reproduced images resembling yet differing from the\noriginal sensation, a coalescence of their resemblances, and finally\nthe substitution of a verbal symbol for these images. With this symbol\nthe intellect operates, and sometimes operates so exclusively with it\nthat not the faintest trace of image or sensation is appreciable--the\nword horse takes the place of the image in the sequence of sensorial\nprocesses, just as the image takes the place of the sensation. It does\nthis as a neural equivalent. In the same way we substitute verbal\nsymbols for a bag of sovereigns when we pay a creditor with a check;\nhe pays the check away to another; and this monetary equivalent passes\nfrom hand to hand without a single coin making its appearance. Does\nthe transaction cease to be commercial, monetary, in this substitution\nof signs? No; nor does a process cease to be psychical when an image\nis substituted for a sensation, and a verbal symbol for an image. This\nevery one will admit. Must we not go further, and extend the admission\nto automatic actions which originally were voluntary, and have now lost\nall trace of ideal prevision, and almost all traces of accompanying\nconsciousness? _The motor mechanism has its symbols also_; in this\nsense, that whereas the action which at first needed complex sensorial\nprocesses to set it going and keep it going, is now determined by a\nsingle one of those processes taking the place of their resultant. When\na practised accountant runs his eye up a column of figures, he does\nnot pause to realize the values of those figures by decomposing the\nsymbols into their numerical units, he simply groups one symbol with\nanother according to their intuited relations, and the final result is\nreached with a certainty not less, and a rapidity far greater, than if\nit had been reached by step-by-step verification. It is thus with the\npianoforte-player. It is thus with all automatic performances, except\nthose dependent on the connate adjustments of the mechanism.\n\n\n\n\nCHAPTER VI.\n\nTHE PROBLEM STATED.\n\n\n71. If the preceding attempt to disengage the question from the\nambiguities of its terms has been successful, we shall find little\ndifficulty in rationally interpreting all the facts adduced in favor\nof Animal Automatism, without having recourse to a mechanical theory\nof biological phenomena. The objections to that theory are that it\nemploys terms which have very misleading _connotations_ even when they\ndo not _denote_ phenomena of widely different orders; so that the moral\nrepugnance commonly felt at the attempt to treat the animal organism as\nif it were a machine, is sustained by the intellectual repugnance at\nthe attempt to explain biological phenomena on principles derived from\nphenomena of a simpler order.\n\nRemark, in passing, this piquant contradiction: the Automaton theory\nof Descartes, when applied to the animals, generally excited ridicule\nor repulsion; whereas the far more inconsistent and mechanical\ntheory of Reflex Action has been almost universally welcomed as a\ngreat discovery, though it banishes the Sensibility which Descartes\npreserved. And further, the philosophers who most loudly protested\nagainst the idea that animals were machines, were the philosophers\nwho most insisted that these animals were made, not evolved--planned\nby their maker, as a watch is planned by its maker, with a distinct\npurpose and prevision in the disposition of every part; whereas the\nphilosophers who most emphatically reject this notion of organisms\nbeing made, are often those who liken organisms to machines.\n\n72. The paradox propounded by Descartes loses much of its strangeness\nwhen we understand his meaning. Its terms are infelicitous because of\ntheir misleading connotations. When he says that all the actions of\nanimals which seem to be due to Consciousness are in fact produced on\nthe same principles as those of a machine, he means that animals have\nnot souls to direct their actions; but since, on being questioned, he\nis ready to admit that animals have sensation, perception, emotion, and\nmemory, his denial of their souls practically comes to much the same as\nthe ordinary position that animals have not Thought nor Consciousness\nof Self.[220] The admission of sensation is, however, quite enough to\nmark the essential difference between an organism and a machine.\n\n73. It was really a great step taken by Descartes when he directed\nattention to the fact that all animal actions were executed in\nstrict conformity with mechanical principles, because both before\nhis time, and since, we may observe a great disregard of the animal\nmechanism, and a disposition to interpret the phenomena on metaphysical\nprinciples. But the connotations of the term \u201cmachine\u201d were such as to\nlead the mind away from the special conditions of the vital mechanism,\nand fix it exclusively on the general conditions of machinery. Hence\nhis opponents misunderstood him, and some of his followers made the\nsame oversight, and ended by eliminating sensation altogether. In\npursuance of this mechanical point of view, to the exclusion of the\nbiological, Thought and even Consciousness have been eliminated from\namong the organic agencies, and are said to have no more influence in\ndetermining even human actions than the whistle of the steam-engine has\nin directing the locomotive. There are thus two _meta_physiological\ntheories. According to the one, Consciousness directs indeed the\nactions of the organism, but is not itself an organic process--it sits\napart, like a musical performer playing on an instrument. According\nto the other, it is not a directing agency, but an accessory product\nof certain organic processes, which processes may go on quite as well\nwithout any accompaniment and interference of Consciousness.\n\n74. Two observations arise here. First, we observe a want of due\nrecognition of the objective and subjective aspects, and their\nrespective criteria. Secondly, we observe mental facts of irresistible\ncertainty interpreted by material hypotheses of questionable value;\nand not only so, but a higher validity is assigned to the material\nhypotheses than to the mental facts they are invented to explain. That\nwe are conscious, and that our actions are determined by sensations,\nemotions, and ideas, are facts which may or may not be explained by\nreference to material conditions, but which no material explanation\ncan render more certain. That animals resemble us in this as in\nother respects is an induction of the highest probability. It is\nalso a fact that many actions take place, as we say, unconsciously\nand involuntarily; and that some take place now consciously, now\nunconsciously. These facts also we endeavor to explain: and when\nwe find that some of the unconscious and involuntary actions take\nplace after the brain has been removed, this is interpreted on the\nmaterial hypothesis of the brain being the sole seat of sensation\nand consciousness; and is urged in favor of the hypothesis that\nconsciousness cannot be an agent in the mechanism. Here the confusion\nof objective and subjective aspects is patent. Consciousness as a\nsubjective fact cannot be a material or objective fact. But may it not\nbe another aspect of that which is objective? So long as we are dealing\nwith the objective aspect, we have nothing but material processes in a\nmaterial mechanism before us. A change within the organism is caused\nby a neural stimulation, and the resulting action is a reflex on the\nmuscles. Here there is simply a transference of motion by a material\nmechanism. There is in this no evidence of a subjective agency;\nthere could be none. But when we come to investigate the process, we\nfind that it differs from similar processes in anorganisms, by the\nnecessary co-operation of special conditions, and among these--the\nvital conditions--there are those which in their subjective aspect we\nexpress not in terms of Matter and Motion, but in terms of Feeling,\ni.\u00a0e. not in objective but in subjective terms. I see a stone move on\nbeing struck; I also see a man shrink on being struck, and hear a dog\nhowl on being kicked. I do not infer that the stone feels as the man\nand dog feel, because I know the stone and the dog to be differently\nconstituted, and infer a corresponding difference in their reactions. I\ninfer that the man and dog feel, because I know they are like myself,\nand conclude that what I feel they feel, under like conditions.\n\n75. Descartes says that animals are sensitive automata. They _always_\nact as we _sometimes_ act, i.\u00a0e. when we are not conscious of what we\ndo, as in singing, walking, playing the piano, etc. We are said to do\nthese things mechanically, automatically, and hence the conclusion that\nthese actions are those of a pure mechanism. But it would be truer to\nsay that we never act mechanically, we always act organically. \u201cWhen\none who falls from a height throws his hands forwards to save his\nhead,\u201d says Descartes, \u201cit is in virtue of no ratiocination that he\nperforms this action\u201d (that depends on the definition: in the Logic\nof Feeling there is a process of ratiocination identical with that in\nthe Logic of Signs). \u201cIt does not depend upon his _mind_\u201d (again a\nquestion of definition), \u201cbut takes place merely because his senses\nbeing affected by _present danger_\u201d (senses, then, have a perception\nof danger?) \u201csome change arises in his brain which determines the\nanimal spirits to pass thence into the nerves in such a manner as is\nrequired to produce this motion, in the same way as in a machine, and\nwithout his mind being able to hinder it. Now since we observe this in\nourselves, why should we be so much astonished if the light reflected\nfrom the body of a wolf into the eye of a sheep has the same force to\nexcite in it the motion of flight?\u201d\n\nHere, both in the case of the man and the sheep, there is presupposed\nthe very mental experience which is denied. The young child will\nnot throw out its arm to protect itself; but after many experiences\nof falling and stumbling, there is an organized perception of the\nimpending danger, and the means of averting it, and it is this which\ndetermines the throwing out of the arms. If this is not a mental\nfact--a process of judgment--then the logical conclusion by which a\nfinancier on hearing a war rumor orders his broker to sell stock, is\nnot a mental fact. The light reflected from the body of a wolf would\nnot disturb the sheep unless its own, or its _inherited_ organized\nexperience were ready there to respond. But this organized experience,\nyou say, enters into the mechanism? Yes; but it cannot be made to\nenter into the mechanism of an automaton, because however complex that\nmechanism may be, and however capable of variety of action, it is\nconstructed solely for definite actions on calculated lines: all its\nreadjustments must have been foreseen, it is incapable of adjusting\nitself to unforeseen circumstances. Hence every interruption in the\nprearranged order either throws it out of gear, or brings it to a\nstandstill. It is regulated, not self-regulating. The organism, on the\ncontrary--conspicuously so in its more complex forms--is variable,\nself-regulating, incalculable. It has _selective adaptation_ (p.\n221) responding readily and efficiently to novel and unforeseen\ncircumstances; _acquiring_ new modes of combination and reaction. An\nautomaton that will learn by experience, and adapt itself to conditions\nnot calculated for in its construction, has yet to be made; till it\nis made, we must deny that organisms are machines. Automatism in the\norganism implies Memory and Perception. A sudden contact--a sudden\nnoise--a vague form seen in the twilight will excite the mechanism\naccording to its organized experiences. We start automatically, before\nwe automatically interpret the cause; we start first, and then ask,\nWhat is that? But we do not always start at sounds or sights which have\nno association with previous experiences. The child and the man both\nsee the falling glass, but the child does not automatically stretch out\na hand to save the glass. Having once learned the action of swimming or\nbilliard-playing, we automatically execute these; without consciously\nremembering the rules, we unconsciously obey them; each feeling as it\nrises is linked on to another, each muscle is combined with others in a\nremembered synthesis.\n\n76. Kempelen\u2019s chess-player surprised the public, but every instructed\nphysiologist present knew that in some way or other its movements were\ndirected by a human mind; simply because no machine could possibly have\nresponded to the unforeseen fluctuations of the human mind opposed to\nit. Even the mind of a dog or a savage would be incompetent to pass\nbeyond the range of its previous experiences, incompetent to seize the\nsignificance of an adversary\u2019s moves on the chessboard. Now just as\nwe conclude that mental agency is essential to a game of chess, so we\nconclude that Sensibility is essential to the fluctuating responses\nof an organism under unforeseen circumstances. We can conceive an\nautomaton dog that would bark at the presence of a beggar; but not of\nan automaton dog that would bark one day at the beggar and the next\nday wag his tail, remembering the food and patting that beggar had\nbestowed. Since all we know of machines forbids the idea of their\nbeing capable of adjusting their actions to new circumstances, or of\nevoking through experience new powers of combination, we conclude that\nwherever this capability of adaptation is present there is an agency in\noperation which does not belong to the class of mechanical agencies.\nGoltz has shown that a frog deprived of its brain manifests so much of\nvision as enables it to avoid obstacles--leaping to the right or to\nthe left of a book placed in its path. This Professor Huxley regards\nas purely mechanical:--\u201cAlthough the frog appears to have no sensation\nof light, visible objects act upon the motor mechanism of its body.\u201d\nShould we not rather conclude that if the frog had no sensation,\nno such effect would follow? because although a machine _might_ be\nconstructed to respond to variations of light and shadows, none could\nbe constructed (without Sensibility) to respond to the fluctuating\nconditions as an organism responds.[221] Were the reflex actions\nof the organism purely mechanical--i.\u00a0e. involving none of those\nfluctuating adjustments which characterize Sensibility--the effect\nwould be uniform, and proportional to the impact; but it is variable,\nand proportional to the static condition of the nervous centres at the\nmoment. Exaggerate this--by strychnine, for instance--and the slightest\ntouch on the skin will produce general convulsions. Lower it--by an\nan\u00e6sthetic--and no reflex at all will follow a stimulus. In an\u00e6sthesia\nof the mucous membrane, no reflex of the eyelid, no secretion of\ntears, follows on the irritation of the membrane; no sneezing follows\nirritation of the inside of the nose; no vomiting follows irritation of\nthe fauces.\n\n77. The question has long ceased to be whether the organism is a\nmechanism. To the physiologist it is this before all things. To the\npsychologist also it has of late years more and more assumed this\ncharacter; because even when he postulates the existence of a spiritual\nentity _in_ the organism but not _of_ it, he still recognizes the\nnecessity of a mechanism for the execution of the acts determined by\nthe spirit; and when the psychologist adopts the theory of spiritual\nphenomena as the subjective aspect of what objectively are material\nphenomena, he of course regards the bodily mechanism and the mental\nmechanism as one and the same real.\n\nThis settled, the problem of Automatism may be thus stated: Granting\nthe animal organism to be a material mechanism, and all its actions\ndue to the operation of that mechanism, are we to conclude that it is\nan automaton essentially resembling the automata we construct, the\nmovements of which may, or may not, be _accompanied_ by Feeling, but\nare in no case _determined_ by Feeling?\n\nDescartes says that animals are sensitive automata. Professor Huxley\nsays that both animals and men are sensitive and conscious automata;\nso that misleading as the language of Descartes and Professor Huxley\noften is in what its terms connote, we do them great injustice if\nwe suppose them to have overlooked the points of difference between\norganisms and machines which have been set forth with so much emphasis\nin a preceding chapter; and the reader is requested to understand that\nwithout pretending to say how much the inevitable connotation of their\nlanguage expresses their opinions, and how much it may have only led\nto their being misunderstood, my criticisms are directed against this\nconnotation and this interpretation.\n\n\n\n\nCHAPTER VII.\n\nIS FEELING AN AGENT?\n\n\n78. Descartes having attributed all animal actions to a sensitive\nmechanism, and indeed all human actions to a similar mechanism,\nendeavored to reconcile this hypothesis with the irresistible facts\nof Consciousness--which assured us that _our_ actions, at least, were\ndetermined by Feeling. To this end he assumed that man had a spiritual\nprinciple over and above the sentient principle. The operation of this\nprinciple was, however, limited to Thought; the actions themselves were\nall performed by the automatic mechanism; so that, in strict logic, the\nconclusion from his premises was the same for man as for animals.\n\nThis conclusion Professor Huxley announced in his Address before the\nBritish Association, 1874[222]--to the great scandal of the general\npublic, which did not understand him aright; and to the scandal also of\na physiological public, which, strangely enough, failed to see that it\nwas the legitimate expression of one of their favorite theories--the\ncelebrated Reflex Theory. Now although it is quite open to any one to\nreject the premises which lead to such a conclusion, if he sees greater\nevidence against the conclusion than for the premises, it is surely\nirrational to accept the premises as those of scientific induction,\nand yet reject the conclusion because it endangers the stability of\nother opinions? For my own part, I do not accept the premises, and my\npolemic will have reference to them.\n\n79. Professor Huxley adopts certain Theses which represent the views\ngenerally adopted by physiologists; to which he adds a Thesis which is\nadopted by few, and which he only puts forward hypothetically. Against\nthese positions I place Antitheses, less generally adopted, but which\nin my belief approximate more nearly to the inductions of experience.\n\n  _Theses._                           _Antitheses._\n\n  I. There can be no sensation        I. There is sensation without\n  without consciousness.              consciousness, if consciousness\n                                      means a special mode of Sentience.\n\n  II. There can be no                 II. The co-operation of the brain\n  consciousness without the           is only necessary for a special\n  co-operation of the brain.          mode of Sentience; other modes are\n                                      active when the brain is inactive.\n\n  III. Sensation and Consciousness    III. Unless the molecular changes\n  are in some inexplicable way        be limited to the brain as the\n  caused by molecular changes in      _occasional_ cause, there is\n  the brain, following upon these     no _following_ of sensation or\n  as one event follows another,       motion, no causal link between the\n  the causal link between motion      two; but the neural process _is_\n  and sensation being a mystery.      the sensation, viewed objectively,\n                                      the sensation is the neural\n                                      process, viewed subjectively. In\n                                      this antithesis, Neural Process\n                                      is not limited to the brain, but\n                                      comprises the whole sensitive\n                                      organism as the _efficient_ cause.\n\n  IV. All actions which take place    IV. All actions are the actions of\n  unconsciously are reflex, and       a reflex mechanism, and all are\n  reflex actions are the operation    sentient, even when unconscious;\n  of an insentient mechanism;         they are therefore never purely\n  they are therefore as purely        mechanical, but always organical.\n  mechanical as those of automata.\n\n  V. The animal body is a reflex      V. Sentience being necessary to\n  mechanism; even when the            reflex action, it is necessarily\n  brain co-operates with the          an agent.\n  other centres, and produces\n  consciousness, this product is\n  not an agent in determining\n  action, it is a collateral\n  result of the operation.\n\n80. The first four Theses are those current in our textbooks, so\nthat it is only the fifth which will have the air of a paradox. Nor,\nas a paradox, is it without advocates. Schiff long ago suggested it\nhypothetically. Hermann mentions it as entertained by physiologists,\nwhom he does not name.[223] Laycock, and, if I remember rightly, Dr.\nDrysdale, have insisted on it; and Mr. Spalding has proclaimed it with\niterated emphasis. Of the Antitheses nothing need be said here, since\nthe whole of this volume is meant to furnish their evidence.\n\nI have already stated that my polemic is against the views that\nProfessor Huxley is _supposed_ to hold by those whom his expressions\nmislead, rather than against the views I imagine him really to hold.\nI have little doubt that he would disavow much that I am forced to\ncombat, although his language is naturally interpreted in that sense.\nBut I do not know in how far he would agree with me, and in the\nfollowing remarks I shall confine myself to what seems to be the plain\ninterpretation of his words, since _that_ is the interpretation which\nhas been generally adopted, and which I most earnestly desire to refute.\n\n81. To begin with this passage. After stating the views of Descartes,\nhe says: \u201cAs actions of a certain degree of complexity are brought\nabout by mere mechanism, why may not actions of still greater\ncomplexity be the result of a more refined mechanism? What proof is\nthere that brutes are other than a superior race of marionnettes, which\neat without pleasure, cry without pain, desire nothing, know nothing,\nand only simulate intelligence as a bee simulates a mathematician?\u201d\nWhat proof? Why, in the first place, the proof which is implied in\nthe \u201cmore refined mechanism\u201d required for the greater complexity of\nactions. In the next place, the proof that the organism of the brute is\nvery different from the mechanism of a marionnette, and is so much more\nlike the organism of man, that since we know man to eat with pleasure\nand cry with pain, there is a strong presumption that the brute eats\nand cries with somewhat similar feelings.\n\n82. Having stated the hypothesis, Professor Huxley says he is not\ndisposed to accept it, though he thinks it cannot be refuted. His chief\nreason for not accepting it is that the law of continuity forbids\nthe supposition of any complex phenomenon suddenly appearing; the\ncommunity between animals and men is too close for us to admit that\nConsciousness could appear in man without having its beginnings in\nanimals. Finding that animals have brains, he justly concludes that\nthey also must have brain functions; and they also therefore must\nbe credited with Consciousness. This argument seems to me to have\nirresistible cogency; and to be destructive not only of the automaton\nhypothesis, but equally of the hypothesis on which the Reflex Theory\nis founded. If the law of continuity forbids the sudden appearance of\nConsciousness, the law of similarity of property with similarity of\nstructure forbids the supposition that central nerve-tissue in one\npart of the system can suddenly assume a totally different property\nin another part. If the brain of an animal, a bird, a reptile, or a\nfish--and _a fortiori_ if the \u0153sophageal ganglia of an insect or a\nmollusc--may be credited with Sensibility, because of the fundamental\nsimilarity of these structures with the structures of the human brain,\nthen surely the spinal cord must be credited with Sensibility; for the\ntissue of the spinal cord is more like that of the brain, than the\nbrain of a reptile is like the brain of a man. The sudden disappearance\nof all Sensibility, on the removal of one portion of the central\nnervous system, would be a violation of the law of continuity. And if\nit be said that Consciousness is not the same as Sensibility, but is a\nspecially evolved function of a specially developed organ, the answer\nwill be that this is only a difference of mode, and that the existence\nof Sensibility is that which renders the automaton and reflex theories\nuntenable.\n\n83. Professor Huxley would probably admit this; for however his\nlanguage may at times seem to point to another conclusion, and is so\nfar ambiguous, he has expressed the view here maintained with tolerable\ndistinctness in the following passage, to which particular attention is\ncalled:--\n\n\u201cBut though we may see reason to disagree with Descartes\u2019 hypothesis,\nthat brutes are unconscious machines, it does not follow that he\nwas wrong in regarding them as automata. _They may be more or less\nconscious sensitive automata_; and the view that they are such\nconscious machines is that which is implicitly or explicitly adopted\nby most persons. When we speak of the actions of the lower animals\nbeing guided by instinct and not by reason, what we really mean is that\nthough they feel as we do, yet their actions are the results of their\nphysical organization. We believe, in short, that they are machines,\none part of which (the nervous system) not only sets the rest in motion\nand co-ordinates its movements in relation with changes in surrounding\nbodies, but is provided with a special apparatus the function of which\nis the calling into existence of those states of consciousness which\nare termed sensations, emotions, and ideas.\u201d\n\n84. To say that they are \u201cconscious automata\u201d seems granting all that\nI demand; but there are two objectionable positions which the phrase\nconceals: first, that Consciousness is not a coefficient; and secondly,\nthat Reflex Action is purely mechanical.\n\nProfessor Huxley nowhere, I think, establishes the distinction\nbetween Consciousness as a term for a special mode of Feeling, and\nConsciousness as the all-embracing term for sentient phenomena. His\nlanguage always implies that an action performed unconsciously is\nperformed mechanically; which may be acceptable if by unconsciously be\nmeant insentiently. I hold that whether consciously or unconsciously\nperformed, the action is equally vital and sentient. In the case he has\ncited of a soldier now living who is subject to periodic alternations\nof normal and abnormal states, in the latter states all the actions\nbeing said to be \u201cunconscious,\u201d we have only to read the account to\nrecognize ample evidence of Sentience. Here is a descriptive passage:--\n\n85. \u201cHis [the soldier\u2019s in the abnormal state] movements remain free,\nand his expression calm, except for a contraction of the brow, an\nincessant movement of the eyeballs, and a chewing motion of the jaws.\nThe eyes are wide open, and their pupils dilated. If the man happens\nto be in a place to which he is accustomed he walks about as usual;\nbut if he is in a new place, or if obstacles are intentionally placed\nin his way, he stumbles against them, _stops, and then feeling over\nthe objects with his hands, passes on one side of them_. He offers\nno resistance to any change of direction which may be impressed upon\nhim, or to the forcible acceleration or retardation of his movements.\nHe eats, drinks, smokes, walks about, dresses and undresses himself,\nrises and goes to bed at the accustomed hours. Nevertheless pins may be\nrun into his body, or strong electric shocks sent through it, without\ncausing the least indication of pain; no odorous substance, pleasant or\nunpleasant, makes the least impression; he eats and drinks with avidity\nwhatever is offered, and takes asaf\u0153tida or vinegar of quinine as\nreadily as water; no noise affects him; and light influences him only\nunder certain conditions.\u201d\n\nThere is no one of these phenomena that is unfamiliar to students of\nmental disease. The case is chiefly remarkable from the periodicity of\nthe recurrence of the abnormal state. I have collected other cases of\nthe kind, and may hereafter find a fitting occasion to quote them.[224]\nThe an\u00e6sthesia and \u201cunconsciousness\u201d noted, no more prove the actions\nperformed by this soldier to have been purely mechanical, i.\u00a0e.\nundetermined by sensation, than an\u00e6sthesia and unconsciousness prove\nsomnambulists and madmen to be machines. In the pathological state\ncalled \u201cecstasy\u201d there is a considerable diminution of sensibility to\nexternal stimuli; with a concentration on certain feelings, images,\ntrains of thought, exhibiting itself in expressions of emotion.\n\u201cLes malades,\u201d says a master, \u201cparaissent enti\u00e8rement absorb\u00e9s par\nleurs mouvements int\u00e9rieurs, ils refusent g\u00e9n\u00e9ralement de manger, et\nsp\u00e9cialement la volont\u00e9 de l\u2019\u00e2me semble compl\u00e8tement enchain\u00e9e.\u201d[225]\n\n86. Observe that while this soldier exhibits such insensibility to\ncertain stimuli, he unequivocally exhibits sensibility to other\nstimuli. All his acts show sense-guidance. Sight and Touch obviously\nregulate his movements. And when he feels objects placed in his way,\nand then passes beside them, wherein does this differ from the normal\nprocedure of sensitive organisms? wherein does it resemble automata?\nDr. Mesmet--from whose narrative the case is cited--remarks that the\nsense of Touch seems to persist \u201cand indeed to be more acute and\ndelicate than in the normal state\u201d; upon which Professor Huxley has\nthis comment:--\u201cHere a difficulty arises. It is clear from the facts\ndetailed that the nervous apparatus by which in the normal state\nsensations of touch are excited is that by which external influences\ndetermine the movements of the body in the abnormal state. But does the\nstate of consciousness, which we term a tactile sensation, accompany\nthe operation of this nervous apparatus in the abnormal state? or\nis consciousness utterly absent, the man being reduced to a pure\nmechanism? It is impossible to obtain direct evidence in favor of the\none conclusion or the other; all that can be said is that the case of\nthe frog shows that the man may be devoid of any kind of consciousness.\u201d\n\n87. It is here we are made vividly aware of the absolute need there is\nto disengage the terms employed from their common ambiguities. All the\nevidence of a tactile sensation which can possibly be furnished, on the\nobjective side, is furnished by the actions of this soldier; to doubt\nit would be to throw a doubt on the sensibility of any animal unable\nto _tell_ us what it felt; nay, even a man if he were dumb, or spoke\na language we could not understand, could give us no other proof. We\nconclude that the soldier had tactile sensations, because we see him\nguided by them as we ourselves are guided by tactile sensations; we\nknow that he is an organism, not a machine, and therefore reject the\ninference that he has become reduced to a \u201cpure mechanism\u201d because\nit is inferred that his consciousness is absent. And on what is this\ninference grounded? 1\u00b0, The belief that the brain is the sole organ\nof consciousness (Sentience)--a belief flatly disproved by the facts,\nwhich show Sentience when the brain has been removed; and 2\u00b0, the\nbelief that the decapitated frog, because it avoids obstacles and\nredirects its leaps to avoid them, does so without Sentience. According\nto the definition we adopt, we may either say that the decapitated\nfrog, and the soldier in his abnormal state, act without consciousness,\nor with it. But what does not seem permissible is to deny that their\nactions exhibit the clearest evidence of _sense-guidance_, and the\nkind of volition which this sense-guidance implies; and this is quite\nenough to separate them from actions of automata. When a man ducks his\nhead to avoid a stone which he sees falling towards him, he assuredly\nhas a sensation, i.\u00a0e. there is a grouping of neural elements, which\nsubjectively is a sensation, and this originates a grouping of other\nneural elements, the outcome of which is a muscular movement, which\nsubjectively is a motor sensation: _this_ grouping would not have\nbeen originated unless the particular grouping had preceded it; nor\nwould the simple retinal stimulus have excited this sensation unless\nthe nerve-centres had been attuned to such response by many previous\nexperiences: the ignorant child would not duck its head on seeing\nthe stone approach. In our familiar use of the word Consciousness it\nwould be correct to say that the man ducks his head \u201cunconsciously\u201d;\nand yet expressing the fact in psychological language, we also say:\nHe ducks his head because _remembering_ the pain of former similar\nexperiences, he _knows_ that if the stone strikes him he will again\nbe hurt as before, therefore he _wills_ to avoid it; expressing it\nin physiological language we may say: The man acts thus because he\nis so organized that a particular neural process is the stimulus of\na particular central discharge; and he became thus organized through\na long series of anterior adjustments responding to stimuli, each\nadjustment being the activity of the vital organism.\n\n88. There can be no doubt that the soldier had perceptions, and that\nthese perceptions guided his movements; whether these shall be called\n\u201cstates of consciousness\u201d or not, is a question of terms. Now since\nwe know that _certain actions are uniformly consequent on certain\nperceptions_, we are justified in inferring that _whenever the\nactions are performed, the perceptions preceded them_: this inference\nmay be erroneous, but in the absence of positive evidence to the\ncontrary it is that which claims our first assent. Is it evidence to\nthe contrary that the perception may have stimulated the action, yet\nbeen unaccompanied by the special mode named consciousness? Not in\nthe least. We learn to read with conscious effort; each letter has\nto be apprehended separately, its form distinguished from all other\nforms, its value as a sign definitely fixed, yet how very rarely are\nwe \u201cconscious\u201d of the letters when we read a book? Each letter is\nperceived; and yet this process passes so rapidly and smoothly, that\nunless there be some defect in a letter, or the word be misspelled,\nwe are not \u201cconscious\u201d of the perceptions. Are we therefore reading\nautomata?[226]\n\nWe are said to walk unconsciously at times; and the continuance of the\nmovement is said to be due to reflex action. But it is demonstrable\nthat the cutaneous sensibility of the soles of the feet is a primary\ncondition. If the skin be insensible, the walking becomes a stumble. In\nlearning to walk, or dance, the child fixes his eyes on his feet, as he\nfixes them on his fingers in learning to play the piano. After a while\nthese registered sensations _connected_ with the muscular sense suffice\nto guide his feet or his fingers; but not if feet or fingers lose their\nsensibility.\n\n89. With these explanations let us follow the further details of this\nsoldier\u2019s abnormal actions:--\n\n\u201cThe man is insensible to sensory impressions made through the ear,\nthe nose, the tongue, and, to a great extent, the eye; nor is he\nsusceptible to pain from causes operating during his abnormal state.\nNevertheless it is possible _so to act upon his tactile apparatus as\nto give rise to those molecular changes in his sensorium which are\nordinarily the causes of associated trains of ideas_. I give a striking\nexample of this process in Dr. Mesmet\u2019s words: \u2018Il se promenait dans\nle jardin, on lui remet sa canne qu\u2019il avait laiss\u00e9 tomber. Il la\npalpe, prom\u00e8ne \u00e0 plusieurs reprises la main sur la poign\u00e9e coud\u00e9e de\nsa canne--devient attentif--semble pr\u00eater l\u2019oreille--et tout \u00e0 coup\nappelle, \u201cHenri! les voil\u00e0!\u201d Et alors portant la main derri\u00e8re son\ndos comme pour prendre une cartouche, il fait le mouvement de charger\nson arme, se couche dans l\u2019herbe \u00e0 plat ventre dans la position d\u2019un\ntirailleur, et suit avec l\u2019arme \u00e9paul\u00e9e tous les mouvements de l\u2019ennemi\nqu\u2019il croit voir \u00e0 courte distance.\u2019 In a subsequent abnormal period\nDr. Mesmet caused the patient to repeat this scene by placing him in\nthe same conditions. Now in this case the question arises whether the\nseries of actions constituting this singular pantomime was accompanied\nby the ordinary states of consciousness, the appropriate trains of\nideas, or not? Did the man dream that he was skirmishing? or was he in\nthe condition of one of Vaucanson\u2019s automata--_a mechanism worked by\nmolecular changes in the nervous system_? The analogy of the frog shows\nthat the latter assumption is perfectly justifiable.\u201d\n\n90. Before criticising this conclusion let me adduce other\nillustrations of this dreamlike activity. \u201cA gentleman whom I attended\nin a state of perfect apoplexy,\u201d says Abercrombie, \u201cwas frequently\nobserved to adjust his nightcap with the utmost care when it got into\nan uncomfortable state: first pulling it down over his eyes, and\nthen turning up the front of it in the most exact manner.\u201d According\nto the current teaching, these actions, which seem like evidence\nof sensation, are nothing of the kind, because--the patient was\n\u201cunconscious\u201d; that is to say, because he did not exhibit one complex\nkind of Sensibility, it is denied that he exhibited another kind!\nhe did not feel discomfort, nor feel the movements by which it was\nrectified--because he could not speak, discuss impersonal questions,\nnor attend to what was said to him! Abercrombie cites other cases: \u201cA\ngentleman who was lying in a _state of perfect insensibility_ from\ndisease of the brain\u201d (note the phrase, which really only expresses\nthe fact that external stimuli did not create their normal reactions)\n\u201cwas frequently observed even the day before his death to take down\na repeating watch from a little bag at the head of his bed, put it\nclose to his ear and make it strike the hour, and then replace it in\nthe bag with the greatest precision. Another whom I saw in a state of\nprofound apoplexy, from which he recovered, had a perfect recollection\nof what took place during the attack, and mentioned many things which\nhad been said in his hearing when he was supposed to be in a state of\nperfect unconsciousness.\u201d Dr. Wigan also tells of a lady whom he knew,\nand who was actually put in a coffin, under the belief that she was\ndead when in a trance. Her sense of hearing was then preternaturally\nacute. In her second-floor bedroom she heard what the servants said\nin her kitchen. When her brother came to see her and he declared she\nshould not be buried until putrefaction set in, she felt intense\ngratitude and a gush of tenderness, but was unable to move even an\neyelid as a manifestation of her feeling. Suddenly all her faculties\nreturned. Dr. Wigan adds that he visited the Countess Escalante, one\nof the Spanish refugees, who remained in a similar state for a short\nperiod, during which she saw her husband and children, and was quite\nconscious of all they did and said--but did not recognize them as her\nown. She was absolutely without the power of moving a finger or of\nopening her mouth. Dr. Neil Arnott told me of a similar case in his\npractice. In these last cases we learn that consciousness--in its\nordinary acceptation--was present, though bystanders could see no trace\nof it. And very often in cases where Consciousness, or at any rate\nSensibility, is clearly manifested, its presence is denied, because the\npatient on recovering his normal condition is quite unable to remember\nanything that he felt and did. Under an\u00e6sthetics patients manifest\nsensation, but on awaking they declare that they felt nothing--of\nwhat value is their declaration? M. Despine tells us of a patient who\nunder chloroform struggled, swore, and cried out, \u201c_Mon Dieu! que\nje souffre!_\u201d yet when the operation was over, and he emerged from\nthe effects of the chloroform, he remembered nothing of what he had\nfelt.[227]\n\n91. Returning now to Dr. Mesmet\u2019s soldier, and to the conclusion that\nhis dreamlike acts were no more than the actions of one of Vaucanson\u2019s\nautomata, surely we are justified in concluding, first, that these\nactions were not of the same kind as those of an automaton, since they\nwere those of a living organism; secondly, that they present all the\nevidence positive and inferential which Sensibility can present in\nthe actions we observe in another, and do not feel in ourselves; and\nthirdly, if with physiologists we agree that the mechanism of these\nactions is \u201cworked by molecular changes in the nervous system,\u201d there\nis some difficulty in understanding how Consciousness, which is said\nto be caused by such changes, could have been absent--how the _cause\ncould operate yet no effect be produced_.\n\n92. What automata can be made to perform is surprising enough, but\nthey can _never_ be made to display the fluctuations of sense-guided\nactions, such as we see in the report of Dr. Mesmet\u2019s soldier:--\n\n\u201cThe ex-sergeant has a good voice, and had at one time been employed\nas a singer at a caf\u00e9. In one of his abnormal states he was observed\nto begin humming a tune. He then went to his room, dressed himself\ncarefully, and took up some parts of a periodical novel which lay\non the bed, as _if he were trying to find something_. Dr. Mesmet,\nsuspecting that he was seeking his music, made up one of these into a\nroll and put it into his hand. _He appeared_ satisfied, took up his\ncane, and went down stairs to the door. Here Dr. Mesmet turned him\nround, and he walked quite contentedly in the opposite direction. The\n_light of the sun_ shining through a window happened to fall upon\nhim, and _seemed to suggest the footlights of the stage_ on which he\nwas accustomed to make his appearance. He stopped, opened his roll of\nimaginary music, put himself in the attitude of a singer, and sang with\nperfect execution three songs one after the other. After which he wiped\nhis face with his handkerchief and drank without a grimace a tumbler of\nstrong vinegar-and-water.\u201d\n\n93. Epileptic patients have frequently been observed going through\nsimilar dreamlike actions in which only those external stimuli which\nhave a relation to the dream seem to take effect.[228] We interpret\nthese as phenomena of _disordered_ mental action, the burden of proof\nlies on him who says they are phenomena of pure mechanism. A mail-coach\ndoes not suddenly cease to be a mail-coach and become a wheelbarrow\nbecause the coachman is drunk, or has fallen from the box. The horses,\nno longer guided by the reins, may dash off the highroad into gardens\nor ditches; but it is their muscular exertions which still move the\ncoach.\n\nCan any one conceive an automaton acting as the sergeant is described\nto be in the following passage?--\n\n\u201cSitting at a table he took up a pen, felt for paper and ink, and began\nto write a letter to his general, in which he _recommended himself for\na medal_ on account of his good conduct and courage. It occurred to\nDr. Mesmet to ascertain experimentally how far vision was concerned in\nthis act of writing. He therefore interposed a screen between the man\u2019s\neyes and his hands; under these circumstances he _went on writing for\na short time, but the words became illegible, and he finally stopped_.\nOn the withdrawal of the screen, he _began to write again where he had\nleft off_. The substitution of water for ink in the inkstand had a\nsimilar result. He stopped, _looked at his pen, wiped it on his coat_,\ndipped it in the water, and began again, with the same effect. On one\noccasion he began to write upon the topmost of ten superposed sheets\nof paper. After he had written a line or two, this sheet was suddenly\ndrawn away. _There was a slight expression of surprise_, but he\ncontinued his letter on the second sheet exactly as if it had been the\nfirst. This operation was repeated five times, so that the fifth sheet\ncontained nothing but the writer\u2019s signature at the bottom of the page.\nNevertheless, when the signature was finished, his eyes turned to the\ntop of the blank sheet, and he went through the form of reading over\nwhat he had written, a movement of the lips accompanying each word;\nmoreover, with his pen _he put in such corrections as were needed_.\u201d\n\n94. Dr. Mesmet concludes that \u201chis patient sees some things and not\nothers; that the sense of sight is accessible to all things which\nare brought into relation with him by the sense of touch, and, on the\ncontrary, is insensible to things which lie outside this relation.\u201d\nIn other words, the sensitive mechanism acts, but acts abnormally.\nThis is precisely what is observed in somnambulists. Yet Professor\nHuxley, who makes the comparison, appears to regard both states as\nthose in which the organism is reduced to a mere mechanism, because\non recovering their normal state the patients are unconscious of what\nhas passed; and because the frog, without its brain, also manifests\nanalogous phenomena. Neither premise warrants the conclusion. I\nhave already touched on the unconsciousness of past actions; let me\nadd the case of Faraday, who was assuredly not an automaton when he\nprepared and delivered a course of lectures which were nevertheless so\nentirely obliterated from his memory that the next year he prepared and\ndelivered the same course once more, without a suspicion that it was\nnot a new one. As to the frog, I must leave that case till I come to\nexamine the evidence on which the hypothesis of the purely mechanical\nnature of spinal action rests.\n\n95. The point never to be left out of sight is that actions which are\nknown to be preceded and accompanied by sensations do not lose their\nspecial character of Sentience, as actions of a sentient mechanism,\nbecause they are not also preceded and accompanied by that peculiar\nstate which is specially called Consciousness, i.\u00a0e. attention to the\npassing changes (comp. p. 403). When we see a man playing the piano,\nand at the same time talking of something far removed from the music,\nwe say his fingers move unconsciously; but we do not conclude that\nhe is a musical machine--muscular sensations and musical sensations\nregulate every movement of his fingers; and if he strikes a false\nnote, or if one of the notes jangles, he is instantly conscious of\nthe fact. Either we must admit that his brain is an essential part\nof the mechanism by which the piano was played, and its function an\nessential agent in the playing; or else we must admit that the brain\nand its function were not essential, and therefore the playing would\ncontinue if the brain were removed. In the latter case, we should have\na musical automaton. That a particular group of sensations, such as\nmusical tones, will set going a particular group of muscular movements,\nwithout the intervention of any _conscious_ effort, is not more to be\ninterpreted on purely mechanical principles, than that a particular\nphrase will cause a story-teller to repeat a familiar anecdote, or an\nold soldier \u201cto fight his battles o\u2019er again.\u201d\n\n96. Let us now pass to another consideration, namely, whether\nConsciousness--however interpreted--is legitimately conceived as a\nfactor in the so-called conscious and voluntary actions; or is merely a\n_collateral result_ of certain organic activities? To answer this, we\nmust first remember that Consciousness is a purely subjective process;\nalthough we may believe it to be objectively a neural process, we are\nnevertheless passing out of the region of Physiology when we speak of\nFeeling determining Action. Motion may determine Motion; but Feeling\ncan only determine Feeling. Yet we do so speak, and are justified. For\nthereby we implicitly declare, what Psychology explicitly teaches,\nnamely, that these two widely different aspects, objective and\nsubjective, are but the two faces of one and the same reality. It\nis thus indifferent whether we say a sensation is a neural process,\nor a mental process: a molecular change in the nervous system, or a\nchange in Feeling. It is either, and it is both, as I have elsewhere\nexplained.[229] There it was argued that the current hypothesis of a\nneural process _causing_ the mental process--molecular movement being\nin some mysterious way _transformed_ into sensation--is not only\ninconceivable, but altogether unnecessary; whereas the hypothesis\nthat the two aspects of the one phenomenon are simply two different\nexpressions, now in terms of Matter and Motion, and now in terms of\nConsciousness, is in harmony with all the inductive evidence.\n\n97. \u201cIt may be assumed,\u201d says Professor Huxley, \u201cthat molecular\nchanges in the brain are the causes of all the states of consciousness\nof brutes. Is there any evidence that these states of consciousness\nmay conversely cause those molecular changes which give rise to\nmuscular motion? I see no such evidence. The frog walks, hops, swims,\nand goes through his gymnastic performances, quite as well without\nconsciousness, and consequently without volition, as with it; and if a\nfrog in his natural state possesses anything corresponding with what\nwe call volition, there is no reason to think that _it is anything but\na concomitant of the molecular changes in the brain_, which _form part\nof the series involved in the production of motion_. The consciousness\nof brutes would appear to be related to the mechanism of their body\nsimply as a collateral product of its working, and to be _as completely\nwithout any power of modifying that working as the steam-whistle which\naccompanies the work of a locomotive engine is without influence\nupon its machinery_. Their volition, if they have any, is an emotion\n_indicative_ of physical changes, not a _cause_ of such changes.\u201d\nParticular attention is called to the passages in italics. In the first\nis expressed a view which seems not unlike the one I am advocating, but\nwhich is contradicted by the second. Let us consider what is implied.\n\n98. When Consciousness is regarded solely under its subjective aspect\nthere is obviously no place for it among material agencies, regarded\nas objective. So long as we have the material mechanism in view we\nhave nothing but material changes. This applies to the frog, with\nor without its brain; to man, supposed to be moved by volition, or\nsupposed to move automatically. The introduction of Consciousness is\nnot the introduction of another agent in the series, but of a new\naspect; the neural process drops out of sight, the mental process\nreplaces it. The question whether we have any ground for inferring\nthat in the series there is included the particular neural state which\nsubjectively is a state of Consciousness, must be answered according\nto the evidence. Well, the evidence shows that the actions do involve\nthe co-operation; and this Professor Huxley expresses when he says that\nthe molecular changes in the brain form part of the series involved in\nthe production of motion. Whether we regard the process objectively\nas a series of molecular changes, or subjectively as a succession of\nsentient changes, the sum of which is on the one side a motor impulse,\non the other a state of consciousness, we must declare Consciousness\nto be an agent, _in the same sense that we declare one change in the\norganism to be an agent in some other change_. The facts are the same,\nwhether we express them in physiological or in psychological terms. The\nphysiologist, having only the material aspect of the organism in view,\nsays, \u201cA cerebral process initiates a motor process\u201d; the psychologist\nsays, \u201cA sensation determines an action.\u201d Unless the two processes have\nbeen linked together by an organic disposition, native or acquired,\nthere will be no such motor process following the cerebral process.\nA dog standing outside the gate is unable to ring the bell, though\nhaving seen another dog ring it, he may wish to do so; but the cerebral\nprocess (his wish) is not linked on to the needful motor process--he\nhas not learned to realize the wish; whereas the other dog, having by\ntrial hit upon the right mode of directing his muscles, has registered\nthis experience, and can ring the bell. The organized disposition\nwhich enables the dog to do this may truly enough be called a\nmodification of the mechanism; but what we have here to note is that a\nsensation originally determined the movement, and always determines it.\n\n99. It is the unfortunate ambiguity of the word Consciousness, and\nthe questionable hypothesis of the brain being the sole seat of\nSensibility, which darken this investigation. Because animals, after\nthe brain has been removed, are seen to perform certain actions\nas deftly as before, they are said to perform these without the\nintervention of Consciousness; when all that is proved by the facts is\nthat these actions are performed without the intervention of the brain.\nIn support of this explanation, examples are cited of unconscious\nactions performed by human beings. But if we assign Sensibility not to\none part of the nervous system exclusively, but to the whole, we can\nreadily understand how the loss of a part will be manifested by very\nmarked changes in the reactions of the whole, and yet not altogether\nprevent the reactions of the parts remaining intact. An animal must\nrespond somewhat differently with and without a brain. One marked\ndifference is the spontaneity of the actions when the brain is intact,\nand the loss of much spontaneity when the brain is injured or removed.\nCerebral processes prompt and regulate actions, as the pressure of the\ndriver on the reins prompts and regulates the movements of the horses;\nbut the carriage is moved by the horses and not by the driver; and the\naction is executed by the motor mechanism, whether the incitation arise\nin a cerebral process or a peripheral stimulation.\n\n100. If we admit that Consciousness is itself an organic process,\naccompanying the molecular changes as a convex surface accompanies\na concave, we must also admit that its fluctuations are adjustments\nand readjustments of the organic mechanism, and that the actions are\nthe effects of these--their resultants. The loss of the brain must\nobviously cause a great disturbance in these adjustments. We may call\nthat a loss of Consciousness, if we choose to limit the term to one\n_mode_ of sentient reaction. But this loss of a mode does not change\nthose reactions which persist so as to convert them into purely\nmechanical reactions. A troop of soldiers may have lost its directing\nofficer, but will fight with the old weapons and the old intelligence,\nthough not with the same convergence of individual efforts. A frog or a\npigeon no more acts as _well_ without a brain as with a brain, than the\ntroop of soldiers fights as well without an officer.\n\n101. Having thus claimed a place for Consciousness in the series of\norganic processes, let us now see whether it has a place among the\nactive agencies. According to Professor Huxley it is not itself an\nagent, but only the \u201ccollateral product of the working of the machine.\u201d\nIt accompanies actions, it does not direct them. It is an index, not a\ncause.\n\nSurely it seems more accurate to say that it accompanies _and_ directs\nthe working? It accompanies the working in two senses: first, as the\nsubjective aspect of the objective process; secondly, as the change\nwhich produces a subsequent change, that is to say, the movements\ninitiated by a feeling are themselves also _felt as they pass_; and\nthis feeling enters into the general stream of simultaneous excitations\nout of which new movements and feelings arise; or to express it\nphysiologically, the sensory impressions determine muscular movements,\nwhich in turn react on the nerve-centres, and these reactions\nblend with the general excitation of reflected and re-reflected\nprocesses.[230] Since every change in Consciousness is a change in\nthe sentient organism, which objectively is a change in the nervous\ncentres, the working of the mechanism being itself a dependent series\nof such changes, each movement must have a reflected influence on the\ngeneral state. This reflected influence may be viewed as a collateral\nproduct of the working; but there is no real analogy between it and\nthe whistle of the steam-engine, because this reflected influence\ndemonstrably _does_ intervene in the _subsequent_ movements. The\nfeeling which accompanies or follows a particular movement cannot\nindeed modify _that_ movement, since that is already set going, or\nhas passed; here there is some analogy to the steam-whistle; but the\nanalogy fails in the subsequent history: no movements whatever of\nthe steam-engine are modified by the whistle which accompanies the\nworking of that engine; yet how the reflected influence modifies the\nworking of the organism! If the hand be passing over a surface, there\nis, accompanying this movement, a succession of muscular and tactile\nfeelings which may be said to be collateral products. But the feeling\nwhich _accompanies_ one muscular contraction _is itself the stimulus_\nof the next contraction; if anywhere during the passage the hand\ncomes upon a spot on the surface which is wet or rough, the change in\nfeeling thus produced, although a collateral product of the movement,\ninstantly changes the direction of the hand, suspends or alters the\ncourse--that is to say, the _collateral product of one movement becomes\na directing factor in the succeeding movement_. Now this is precisely\nwhat no automaton can effect, unless for changes that are prearranged.\nA steam-engine drives its locomotive over the rails, be they smooth\nor rough, entire or broken; it whistles as it goes, but no whistling\ndirects and redirects its path.\n\n102. Volition is said to be an \u201cemotion indicative of physical changes,\nnot a cause of such changes.\u201d Here it is necessary to understand in\nwhat sense the term cause is employed. I should prefer stating the\nproposition thus: a volition is a state of the sentient organism,\nindicative of physical changes which have taken place, and of changes\nwhich will take place. Because it is the _expression_ of the first\ngroup of changes, it cannot be their _origin_; but it can be, and is\nthe origin of the second group, which it initiates. The indignation\nexcited by an insult or a blow is not the origin of the emotion or\nthe pain, but it is the origin of the actions which are prompted by\nthis sentient state. In fact no sooner do we admit that the organism\nis a sentient mechanism, than the conclusion is irresistible that\nSensibility is a factor in the working of that mechanism.\n\n103. \u201cMuch ingenious argument,\u201d says Professor Huxley, \u201chas at various\ntimes been bestowed upon the question: How is it possible to imagine\nthat volition which is a state of consciousness, and as such has not\nthe slightest community of nature with matter and motion, can act upon\nthe moving matter of which the body is composed, as it is assumed to do\nin voluntary acts? But if, as is here suggested, the voluntary acts of\nbrutes--or in other words, the acts which they desire to perform--are\nas purely mechanical as the rest of their actions, and are simply\naccompanied by the state of consciousness called volition, the inquiry,\nso far as they are concerned, becomes superfluous. Their volitions\ndo not enter into the chain of causation of their actions at all....\nAs consciousness is brought into existence only as the consequence\nof molecular motion in the brain, it follows that it is an indirect\nproduct of material changes. The soul stands related to the body as the\nbell of a clock to the works, and consciousness answers to the sound\nwhich the bell gives out when it is struck.\u201d This has been answered in\nthe foregoing pages; nor do I think the reader who has recognized the\nambiguity of the term Consciousness, and the desirability of replacing\nit in this discussion by the less equivocal term Sentience, will need\nmore to be said.\n\n104. The important question whether reflex actions are insentient, and\ntherefore mechanical, will occupy us in the next problem. The question\nof Automatism which has been argued in the preceding chapters, may,\nI think, be summarily disposed of by a reference to the irresistible\nevidence each man carries in his own consciousness that his actions\nare frequently--even if not always--determined by feelings. He is\nquite certain that he is not an automaton, and that his feelings are\nnot simply collateral products of his actions, without the power of\nmodifying and originating them. Now this fundamental fact cannot be\ndisplaced by any theoretical explanation of its factors. Nor would\nthis fundamental truth be rendered doubtful, even supposing we were to\ngrant to the full all that is adduced as evidence that _some_ actions\nwere the result of purely mechanical processes without sentience at\nall. I am a conscious organism, even if it be true that I sometimes act\nunconsciously. I am not a machine, even if it be true that I sometimes\nact mechanically.\n\n\n\n\nPROBLEM IV.\n\nTHE REFLEX THEORY.\n\n    \u201cSi omnes patres sic, et Ego non sic.\u201d--ABELARD, _Sic et Non_.\n\n    \u201cWill man bestimmen wo der Mechanismus aufh\u00f6rt und wo der Wille\n    anf\u00e4ngt so ist die Frage \u00fcberhaupt falsch gestellt. Denn man setzt\n    hier Begriffe einander gegen\u00fcber die gar keine Gegens\u00e4tze sind.\n    Vorgebildet in den mechanischen Bedingungen des Nervensystems sind\n    _alle_ Bewegungen.\u201d--WUNDT, _Physiologische Psychologie_.\n\n    \u201cSollte die so durchsichtige Homologie zwischen Hirn and\n    R\u00fcckenmark, wie solche sich schlagend in Bau und Entwicklung\n    darthut, wesentlich andere physiologische Qualit\u00e4ten\n    bedingen?\u201d--LUSCHINGER in _Pfl\u00fcger\u2019s Archiv_, Bd. XIV. 384.\n\n\n\n\nTHE REFLEX THEORY.\n\n\n\n\nCHAPTER I.\n\nTHE PROBLEM STATED.\n\n\n1. The peculiarity of the Reflex Theory is its exclusion of Sensibility\nfrom the actions classed as reflex; in consequence of which, the\nactions are considered to be \u201cpurely mechanical.\u201d\n\nNo one denies that most of the reflex actions often have conscious\nsensations preceding and accompanying them, but these are said not\nto be essential to the performance of the actions, because they may\nbe absent and the actions still take place. It is notorious that we\nbreathe, wink, swallow, etc., whether we are conscious of these actions\nor not. Our conclusion therefore is that these peculiar states of\nConsciousness are _accessory_, not essential to the performance of\nthese actions. The fact is patent, the conclusion irresistible. But\nnow consider the equivoque: because an action takes place without our\nbeing conscious of it, the action is said to have had no sensation\ndetermining it. This, which is a truism when we limit Consciousness to\none of the special modes Of Sensibility, or limit sensation to this\nlimited Consciousness, is a falsism when we accept Consciousness as\nthe total of all combined sensibilities, or Sensation as the reaction\nof the sensory mechanism. That a reflex action is determined by the\nsensory mechanism, no one disputes; whether the reaction of a sensory\nmechanism shall be called a sensation or not, is a question of terms.\nI have shown why it must be so called if anything like coherence is to\nbe preserved in physiological investigations; and I have more than once\nsuggested that the fact of intellectual processes taking place at times\nwith no more consciousness than reflex actions, is itself sufficient to\nshow that a process does not lapse from the mental to the mechanical\nsphere simply by passing unconsciously.\n\nInasmuch as an organism is a complex of organs, its total function must\nbe a complex of particular functions, each of which may analytically\nbe treated apart. Vitality is the total of all its physiological\nfunctions, and Consciousness the total of all its psychological\nfunctions. But inasmuch as it is only in its relation to the whole that\neach part has functional significance, and cannot therefore be isolated\nin reality, as it is in theory--cannot live by itself, act by itself,\nindependently of the organism of which it is an organ, there is strict\naccuracy in saying that no particular sensation can exist without\ninvolving Consciousness; for this is only saying that no sensory organ\ncan react without at the same time involving a reaction of the general\nsensorium. But since this general sensorium is simultaneously affected\nby various excitations each of which is a force, every sensation,\nperception, emotion, or volition is a _resultant_ of the composition\nof these forces; and as there can be only one resultant at a time, to\nbe replaced by another in swift succession, this one represents the\n_state_ of Consciousness, and this state may or may not be felt under\nthe peculiar _mode_ named \u201cConsciousness,\u201d in its special meaning. In\nother words, the reaction of a sensory organ is always sentient, but\nnot always consentient.\n\n2. Let us illustrate this by the sensation of musical tone. When\nwe hear a tone we are affected not only by the fundamental tone,\nrepresenting the vibrations of the sounding body as a whole, but\nalso by the harmonics or overtones, representing the vibrations of\nthe several parts of that whole. It is these latter vibrations which\ngive the tone its timbre, or peculiar _quality_; and as the harmonics\nare variable with the variable structure of the vibrating parts, two\nbodies which have the same fundamental tone may have markedly different\nqualities. There are some tones which are almost entirely free from\nharmonics; that is to say, their harmonics are too faint for our ear to\nappreciate them, though we know that the vibrations must be present.\nApply this to the excitations of the sensorium. Each excitation will\nhave its fundamental feeling, and more or less accompanying thrills of\nother feelings: it is these thrills which are the harmonics, giving to\neach excitation its specific quality; but they may be so faint that no\nspecific quality is discriminated. A fly settles on your hand while you\nare writing, the faint thrill which accompanies this excitation of your\nsensory nerve gives the specific sensation of tickling, and this causes\nyou to move your hand with a jerk. If your attention is preoccupied,\nyou are said to be unconscious of the sensation, and the jerk of\nyour hand is called a reflex action; but if your attention is not\npreoccupied, or if the thrill is vivid, you are said to be conscious\nof the sensation, and the action is no longer reflex, but volitional.\nObviously here the difference depends not on the sentient excitation by\nan impression on the nerve, but on the state of the general sensorium\nand its consequent reaction. Had not the impression been carried to the\nsensorium, no movement would have followed the fly\u2019s alighting on your\nhand, because no sensation (sensory reaction) would have been excited;\nthe hypothesis of a purely mechanical reflex is quite inadmissible.\n\n3. Or take another case. It sometimes happens that we fall asleep\nwhile some one is reading to us aloud. The sounds of the reader\u2019s\nvoice at first awaken the familiar thrills which give the tones their\nquality, and the words their significance; but gradually as sleep\nsteals over us, the organism ceases to react thus; the words lose more\nand more of their significance, the tones lose more and more of their\nharmonics; at last we pass into the state of unconsciousness--we cease\nto hear what is read. But do we cease to feel? We have not _heard_,\nbut we have been _affected_ by the sounds. Not by distinguishable\nsensations; nevertheless a state of the general Sensibility has been\ninduced. To prove that we have been affected is easy. Let the reader\nsuddenly cease, and if our sleep be not too profound, we at once awake.\nNow, unless the sound of his voice had affected us, it is clear that\nthe cessation of that could not have affected us. Or let us suppose\nour sleep to be unbroken by the cessation of the sound; even this will\nnot prove that we have been unaffected by the sounds, it will merely\nprove that those sounds, or their cessation, did not excite a conscious\nstate. For let the reader, in no louder tone, ask, \u201cAre you asleep?\u201d\nand we start up, with round eyes, declaring, \u201cNot at all.\u201d Nay, should\neven this question fail to awaken us, the speaker need only utter some\nphrase likely to excite a thrill--such as, \u201cThere\u2019s the postman!\u201d or,\n\u201cI smell fire!\u201d and we start up.\n\nI remember once trying the experiment on a wearied waiter, who had\nfallen asleep in one of the unoccupied boxes of a tavern. His arm\nrested on the table, and his head rested on his arm: he snored the\nsnore of the weary, in spite of the noisy laughter and talk of the\nguests. I called out \u201cJohnson,\u201d in a loud tone. It never moved him. I\nthen called \u201cWilson,\u201d but he snored on. No sooner did I call \u201cwaiter,\u201d\nthan he raised his head with a sleepy \u201c_yessir_.\u201d Now, to suppose, in\nthis case, that he had _no_ sensation when the words \u201cJohnson\u201d and\n\u201cWilson\u201d reached his ears, but had a sensation when the word \u201cwaiter\u201d\nreached his ears, is to suppose that two similar causes will not\nproduce a similar effect. The dissyllable \u201cJohnson\u201d would excite as\npotent a reaction of his sensory organ as the dissyllable \u201cwaiter\u201d;\nbut the thrills--the reflex feelings--were different, because the word\n\u201cJohnson\u201d was not associated in his mind with any definite actions,\nwhereas the word \u201cwaiter\u201d was so associated as to become an automatic\nimpulse.[231]\n\n4. Two sisters are asleep in the same bed, and a child cries in the\nnext room. The sounds of these cries will give a similar stimulus\nto the auditory nerve of each sister, and excite a similar sensory\nreaction in each. Nevertheless, the one sister sleeps on undisturbed,\nand is said not to hear the cry. The other springs out of bed, and\nattends to the child, because she being accustomed to attend on the\nchild and soothe it when crying, the primary sensation has excited\nsecondary sensations, thrills which lead to accustomed actions. Could\nwe look into the mind of the sleeping sister, we should doubtless find\nthat the sensation excited by the child\u2019s cry had merged itself in\nthe general stream, and perhaps modified her dreams. Let her become a\nmother, or take on the tender duties of a mother, and her vigilance\nwill equal that of her sister; because the cry will _then_ excite a\ndefinite reflex feeling, and a definite course of action. But this very\nsister, who is so sensitive to the cry of a child, will be undisturbed\nby a much louder noise; a dog may bark, or a heavy wagon thunder along\nthe street, without causing her to turn in bed.[232]\n\nAlthough during sleep the nervous centres have by no means their\nfull activity, they are always capable of responding to a stimulus,\nand sensation will always be produced. When the servant taps at your\nbedroom door in the morning, you are said not to hear the tap, if\nasleep; you do not perceive it; but the sound reaches and rouses you\nnevertheless, since when the second tap comes, although no louder, you\ndistinctly recognize it. In etherized patients, sensation is constantly\nobserved returning before any consciousness of what is going on\nreturns. \u201cI was called,\u201d says Mr. Potter, \u201cto give chloroform to a lady\nfor the extraction of ten teeth. The first five were extracted without\nthe slightest movement, but as the operation proceeded, sensation\nreturned, and I was obliged to use considerable force to keep her in\nthe chair during the extraction of the last tooth. She came to herself\nvery shortly after, and was delighted to find she had got over all her\ntroubles without having felt it the least in the world.\u201d[233]\n\n5. We do not see the stars at noonday, yet they shine. We do not see\nthe sunbeams playing among the leaves on a cloudy day, yet it is by\nthese beams that the leaves and all other objects are visible. There\nis a general illumination from the sun and stars, but of this we are\nseldom aware, because our attention falls upon the illumined objects,\nbrighter or darker than this general tone. There is a sort of analogy\nto this in the general Consciousness, which is composed of the sum of\nsensations excited by the incessant simultaneous action of internal\nand external stimuli. This forms, as it were, the daylight of our\nexistence. We do not habitually attend to it, because attention falls\non those particular sensations of pleasure or of pain, of greater\nor of less intensity, which usurp a prominence among the objects of\nthe sensitive panorama. But just as we need the daylight to see\nthe brilliant and the sombre forms of things, we need this living\nConsciousness to feel the pleasures and the pains of life. It is\ntherefore as erroneous to imagine that we have no other sensations than\nthose which we distinctly recognize--as to imagine that we see no other\nlight than what is reflected from the shops and equipages, the colors\nand splendors which arrest the eye.\n\nThe amount of light received from the stars may be small, but it is\npresent. The greater glory of the sunlight may render this starlight\ninappreciable, but it does not render it inoperative. In like manner\nthe amount of sensation received from some of the centres may be\ninappreciable in the presence of more massive influences from other\ncentres; but though inappreciable it cannot be inoperative--it must\nform an integer in the sum.\n\n6. The reader\u2019s daily experience will assure him that over and above\nall the particular sensations capable of being separately recognized,\nthere is a general stream of Sensation which constitutes his feeling\nof existence--the Consciousness of himself as a sensitive being. The\nebullient energy which one day exalts life, and the mournful depression\nwhich the next day renders life a burden almost intolerable, are\nfeelings not referable to any of the particular sensations, but arise\nfrom the massive yet obscure sensibilities of the viscera, which form\nso important a part of the general stream of Sensation. Some of these\nmay emerge into distinct recognition. We may feel the heart beat, the\nintestines move, the glands secrete; anything _unusual_ in their action\nwill force itself on our attention.\n\n\u201cWhat we have been long used to,\u201d says Whytt, \u201cwe become scarcely\nsensible of; while things which are new, though much more trifling,\nand of weaker impression, affect us remarkably. Thus he who is wont to\nspend his time in the country is surprisingly affected, upon first\ncoming into a populous city, with the noise and bustle which prevail\nthere: of this, however, he becomes daily less sensible, till at length\nhe regards it no more than they who have been used to it all their\nlifetime. The same seems to be the case also with what passes within\nour bodies. Few persons in health feel the beating of their heart,\nthough it strikes against their ribs with considerable force every\nsecond; whereas the motion of a fly upon one\u2019s face or hands occasions\na very sensible and uneasy titillation. The pulsation of the great\n_aorta_ itself is wholly unobserved by us; yet the unusual beating of a\nsmall artery in any of the fingers becomes very remarkable.\u201d\n\n7. A large amount of sensation is derived from the muscular sense, yet\nwe are not aware of the nice adjustments of the muscles, regulated by\nthis sensibility, when we sit or walk. No sooner are we placed in an\nexceptional position, as in walking on a narrow ledge, than we become\ndistinctly aware of the effort required to preserve equilibrium. It is\nnot the novelty of the position which has increased our sensibility;\nthat has only caused us to attend to our sensations. In like manner,\nthe various streams of sensation which make up our general sense\nof existence, separately escape notice until one of them becomes\nobstructed, or increases in impetuosity. When we are seated at a\nwindow, and look out at the trees and sky, we are so occupied with the\naspects and the voices of external Nature, that no attention whatever\nis given to the fact of our own existence; yet all this while there\nhas been a massive and diffusive feeling arising from the organic\nprocesses; and of this we become distinctly aware if we close our\neyes, shut off all sounds, and abstract the sensations of touch and\ntemperature--it is then perceived as a vast and powerful stream of\nsensation, belonging to none of the special Senses, but to the System\nas a whole. It is on this general stream that depend those well-known\nbut indescribable states named \u201cfeeling well\u201d and \u201cfeeling ill\u201d--the\n_bien \u00eatre_ and _malaise_ of every day. Of two men looking from the\nsame window, on the same landscape, one will be moved to unutterable\nsadness, yearning for the peace of death; the other will feel his soul\nsuffused with serenity and content: the one has a gloomy background,\ninto which the sensations excited by the landscape are merged; the\nother has a happy background, on which the sensations play like\nripples on a sunny lake. The tone of each man\u2019s feeling is determined\nby the state of his general consciousness. Except in matters of pure\ndemonstration, we are all determined towards certain conclusions as\nmuch by this general consciousness as by logic. Our philosophy, when\nnot borrowed, is little more than the expression of our personality.\n\n8. Having thus explained the relation of particular sensations to the\ngeneral state of Consciousness considered as the function of the whole\norganism, we may henceforward speak of particular sentient states, as\nwe speak of particular organs and functions, all the while presupposing\nthat the organs and functions necessarily involve the organism, since\n_apart_ from the organism they have no such significance. The reaction\nof a sensory organ is therefore always a sentient phenomenon. Apart\nfrom the living organism there can be no such vital reaction, but only\na physical reaction. It is commonly supposed that sensation is simply\nthe molecular excitation of the cerebrum; yet no one will maintain\nthat if the cerebrum of a corpse be excited, by a galvanic current\nsent through the optic nerve, for instance, this excitation will be a\nsensation. Whence we may conclude that it is not the physical reaction\nor stimulus which constitutes sensation, but the physiological reaction\nof the living organism.\n\n9. Now this is the point which the advocates of the Reflex Theory,\nimplicitly or explicitly, always deny. Let us trace the origin of the\nfallacy, if possible. When we remove the eye from a recently killed\nanimal, and let a beam of light fall on it, the pupil contracts. This\nis a purely mechanical action; no one would suggest that a sensation\ndetermined it. When we remove the leg, and irritate its nerve, the leg\nis jerked out. This is also a purely mechanical action. When we remove\nthe brain from an animal, and pinch its toes, the leg is withdrawn\nor the pincers are pushed aside. Is this equally a purely mechanical\naction? And if not, why not?\n\nThe Reflex Theory would have us believe that all three cases were\nmechanical, at least in so far as they were all destitute of sentient\nco-operation, the ground for this conclusion being the hypothesis that\nthe brain is the exclusive seat of sensation. The Reflex Theory further\nconcludes that since these, and analogous actions, are performed when\nthe brain is removed, they, being thus independent of sentience, may\nbe performed when the brain is present without any co-operation of\nsentience. The grounds for this conclusion being the facts that in\nthe normal state of the organism there are many actions of which we\nare sometimes conscious, and at other times unconscious; and some\nactions--such as the dilatation and contraction of the pupil--of which\nwe are never conscious. This observation of parts detached from the\norganism seems confirmed by observation of actions passing in our\nown organisms, both converging to the conclusion that the actions in\nquestion are purely mechanical, involving no sentience whatever. We are\ntaught, therefore, that there is besides the sentient mechanism, to\nwhich all conscious actions are referred, a reflex mechanism, to which\nall unconscious actions are referred. The cerebro-spinal axis, acting\nas a whole, constitutes the first; the spinal axis, acting without the\nco-operation of the cerebrum, constitutes the second.\n\n10. Before proceeding with our exposition of the theory it may be\nwell to state two considerations which must be constantly in view. If\nit should appear that there is any reasonable evidence for refusing\nto limit Sensibility to the cerebrum--and this evidence I shall\nadduce--the Reflex Theory must obviously be remodelled. Nor is this\nall. We might see overwhelming evidence in favor of the hypothesis that\nthe cerebrum is the exclusive seat of Sensibility, and still reject as\na fallacy the conclusion that because certain actions can be performed\nin the absence of the cerebrum, therefore those actions in the normal\norganism are likewise performed without cerebral co-operation. I\nmean that it is a fallacy to conclude from the contractions of the\npupil, and the jerking of the leg, when eye and leg are detached\nfrom the organism, that therefore when eye and leg form integral\nparts of the organism, such contractions and jerkings are mechanical\nreflexes without sentient conditions. And the fallacy is analogous\nto that which would conclude from the observations of a mechanical\nautomaton, that similar appearances in a vital organism were equally\nautomatic and mechanical. So long as both sets of phenomena are\napprehended simply as they appear to the sense of sight, they may be\nindistinguishable; but no sooner do we apprehend them through other\nmodes, and examine the _modes of production_ of the phenomena, than\nwe come upon cardinal differences. A limb detached from the organism\nis like a phrase detached from a sentence: it has lost its vital\nsignificance, its functional value, in losing its connection with the\nother parts. The whole sentence is necessary for the slightest meaning\nof its constituent words, and each word is a language-element only\nwhen ideally or verbally connected with the other words required to\nform a sentence; without subject, predicate, and copula, no sentence\ncan be formed. So the organic connexus of parts with a living whole is\nnecessary for the simplest function of each organ; and a limb, or any\nother part, is a physiological element only when (ideally or really)\nan integral of a vital whole. The organism may be truncated by the\nremoval of certain parts, as the sentence may be abbreviated by the\nremoval of certain phrases; but so long as subject, predicate, and\ncopula remain, there is a meaning in the sentence; and so long as the\norganic connexus needful for vitality remains, there will be vital\nfunction. The eye detached from the organism is no longer a part of\nthe living whole, it no longer lives, its phenomena cease to be vital,\nits movements cease to have sentient conditions. The movements of the\npupil may seem to be the same as those of the living eye; but when we\ncome to examine their modes of production, we learn that they are not\nthe same. The stimulus of light falling on the eye in the two cases\nnecessarily has a different effect, because the effect is the result of\nthe co-operating causes, and the co-operation in the one case is that\nof a lifeless organ, in the other that of a living organism. So long as\nthe eye forms an integral part of the organism, every stimulus acting\non the eye necessarily acts on the organism, and every reaction of the\norgan is necessarily conditioned by the state of the organism. Further,\nevery stimulation of a sensory nerve necessarily affects the general\nsensorium, since the whole nervous system is structurally continuous\nand functionally co-operant. (See Prob. II. \u00a7 16.) Therefore, the\nstimulation of the eye, although too faint to be discriminated as a\nconscious sensation, must enter as a sentient tremor into the general\nstream of Sentience; and although we have no test delicate enough to\nreveal this operation, we know the _obverse_ operation of conscious\nsensation on the movements of the pupil--in surprise, for example, the\npupil is dilated.\n\n11. There are still stronger reasons for asserting that the spinal\nreflexes are necessarily conditioned by the general state of the\nsensorium, so that in the normal organism we cannot legitimately\nexclude them from Sentience; and the Reflex Theory is therefore\nunphysiological, even on the hypothesis that the cerebrum is the\nexclusive seat of Sensibility. This hypothesis, however, seems to\nme untenable; and all the observed facts which it is invented to\nexplain admit of a far more consistent explanation. It is irrational\nto suppose that a limb, detached from the body, _felt_ the stimulus\nwhich caused its muscles to contract. The limb is not a living\norganism, having a sentient mechanism in its nervous mechanism. Not\nless irrational is it to suppose that when the limb forms an integral\npart of a living organism, with a sentient mechanism of nerves and\nnerve-centres, this organism does not react on the stimulus which\nexcites the muscles of the limb to contract; nor, pursuing the same\ntrain of reasoning, is it irrational to suppose that when this living\norganism has been mutilated, and certain parts destroyed, which do\nnot in their destruction prevent the connexus of the rest, but leave\nintact a sentient mechanism of nerves and nerve-centres, then also this\ntruncated organism still reacts as a whole, still feels the stimulus\nwhich causes the muscles of the limb to contract. Hypothesis for\nhypothesis, we may at least say that the one is as reasonable as the\nother. And I shall be disappointed if, when the reader has gone through\nall the evidence hereafter to be adduced, he does not conclude that\nthe hypothesis which assigns Sensibility to the nervous mechanism as a\nwhole is not the more acceptable of the two.\n\n12. Let us now pursue our exposition of the Reflex Theory. All that\nwe have endeavoured to establish respecting the essential identity of\nthe processes in conscious and unconscious states, and voluntary and\ninvoluntary actions,--an identity which does not exclude differences of\ndegree corresponding with these different terms,--is ignored or denied\nin the Reflex Theory. Whereas I suppose all processes to be reflex\nprocesses, some of them having the voluntary, others the involuntary\ncharacter, physiologists generally distinguish the involuntary as\nreflex, and invent for this class a special mechanism. According to\nMarshall Hall, who originated the modern form of this theory, actions\nare divisible into four distinct classes: the _voluntary_, dependent\non the brain; the _involuntary_, dependent on the irritability of\nthe muscular fibre; the _respiratory_, wherein \u201cthe motive influence\npasses in a _direct line_ from one point of the nervous system to\ncertain muscles\u201d; and the _reflex_, dependent on the \u201ctrue spinal\nsystem\u201d of _incident-excitor_ nerves, and of _reflex-motor_ nerves.\nThese last-named actions are produced when an _impression_ on the\nsensitive surface is conveyed, by an excitor-nerve, to the spinal\ncord, and is there _reflected_ back on the muscles by a corresponding\nmotor-nerve. In this process _no_ sensation whatever occurs. The action\nis purely reflex, purely _excito-motor_--like the action of an ordinary\nmechanism.[234]\n\nM\u00fcller, who shares with Marshall Hall the glory of having established\nthis classification, thinks that although the absence of sensation is\na characteristic of the reflex actions, these actions may be, and are\nat times, accompanied by sensation. \u201cThe view I take of the matter is\nthe following: Irritation of sensitive fibres of a spinal nerve excites\nprimarily a centripetal action of the nervous principle conveying the\nimpression to the spinal cord; if the centripetal action can then be\ncontinued to the _sensorium commune_, a true sensation is the result;\nif, on account of division of the cord, it cannot be communicated to\nthe sensorium, it still exerts its whole influence upon the cord; in\nboth cases a reflex motor action may be the result.\u201d[235]\n\n13. It is needless nowadays to point out that the existence of a\ndistinct system of excito-motor nerves belongs to Imaginary Anatomy;\nbut it is not needless to point out that the Imaginary Physiology\nfounded on it still survives. The hypothetical process seems to me not\nless at variance with observation and induction, than the hypothetical\nstructure invented for its basis. We have already seen that what\nAnatomy positively teaches is totally unlike the reflex mechanism\npopularly imagined. The sensory nerve is not seen to enter the spinal\ncord at one point, and pass over to a corresponding point of exit; it\nis seen to enter the gray substance, which is continuous throughout the\nspinal cord; it is there lost to view, its course being untraceable.\nNor does the physiological process present the aspect demanded by the\ntheory: it is not that of a direct and uniform reflexion, such as\nwould result from an impression on one spot transmitted across the\nspinal cord to a corresponding motor-nerve. The impression is sometimes\nfollowed by one movement, sometimes by another very different movement,\neach determined by the state of neural tension in the whole central\nsystem.\n\nEven the facts on which the Reflex Theory is based are differently\ninterpreted by different physiologists. Van Deen, for instance,\nconsiders that Reflexion takes place without Volition, but not\nwithout Sensation; and Budge, that it takes place without perception\n(_Vorstellung_). And when it is remembered that most of the reflex\nactions will be accompanied by distinct consciousness whenever\nattention is directed to them, or the vividness of the stimulation\nis slightly increased, it becomes evident that the absence of\nConsciousness (discrimination) is not the differentia of Reflex action.\n\n14. Nor can the absence of spontaneity be accepted as a differentia.\n_All_ actions are excited by stimulation, internal or external. What\nare called the spontaneous actions are simply those which are prompted\nby internal, or by not recognizable stimuli; and could we see the\nprocess, we should see a neural change initiated by some stimulation,\nwhether the change was conscious and volitional, or unconscious and\nautomatic. The dog rising from sleep and restlessly moving about,\nis acting spontaneously, whether the stimulation which awakens him\nbe a sensation of hunger, a sensation of sound, the sharp pain of a\nprick, or a dash of cold water. If he wags his tail at the sight of\nhis master, or wags it when dreaming, the stimulation is said to be\nspontaneous; but if after his spinal cord has been divided the tail\nwags when his abdomen is tickled, the action is called reflex. In all\nthree cases there has been a process of excitation and reflexion.\n\n15. The advocates of the Reflex Theory insist that spontaneity is\nalways absent in brainless animals; whence the conclusion that the\nbrain is the exclusive organ of sensation. But the fact asserted is\ncontradicted by the evidence. No experimenter can have failed to\nobserve numberless examples of spontaneity in brainless animals. Many\nexamples have already been incidentally noticed in previous pages. Let\nme add one more from my notes: I decapitated a toad and a triton, and\ndivided the spinal cord of another triton and a frog. At first the\nmovements of the decapitated animals were insignificant; but on the\nsecond day the headless toad was quite as lively as the frog; and the\nheadless triton little less so than his companion with cord divided\nbut brain intact. I have, at the time of writing this, a frog whose\ncord was divided some weeks ago. He remains almost motionless unless\nwhen touched; he is generally found in the same spot, and in the same\nattitude to-day as yesterday, unless touched, or unless the table be\nshaken. He occasionally moves one of the forelegs; occasionally one of\nthe hind-legs; but without changing his position. If he were brainless,\nthis quiescence would be cited in proof of the absence of spontaneity\nin the absence of the brain; but this conclusion would be fallacious,\nand is seen to be so in the spontaneous movements of his companion who\nhas _no_ brain.\n\n16. With spontaneity is associated the idea of volition, and with\nvolition _choice_. Now I admit that it is complicating the question to\nask any one to conceive a headless animal choosing one action rather\nthan another; but it is equally difficult to reconcile ourselves to\nthe idea of \u201cchoice\u201d in contemplating the actions of a mollusc. In\nwhat sense we can speak of the volition of a mollusc or an insect has\nalready been considered (p. 408). When a man in a fit of coughing\nseizes a glass of water to allay the tickling in his throat, we have\nno hesitation in declaring this to be volitional--and the remedy to\nbe _chosen_. But when a brainless animal adopts some _unusual_ means,\nafter the failure of the usual means, to allay an irritation, we still\nhesitate to call the action volitional. I see, however, no objection to\ncalling it the adaptation of a sensitive mechanism which is markedly\nunlike any inorganic mechanism.\n\nPlace a child of two or three years old upon his back, and tickle\nhis right cheek with a feather. He will probably move his head away.\nContinue tickling, and he will rub the spot with his right hand,\n_never_ using the left hand for the right cheek, so long as the right\nhand is free; but if you hold his right hand, he will use the left.\nDoes any one dispute the voluntary character of these actions?\n\nNow compare the actions of the sleeping child under similar\ncircumstances, and their sequence will be precisely similar. This\ncontrast is the more illustrative, because physiologists generally\nassume that in sleep consciousness and volition are _suspended_.\nThey say: \u201cThe brain sleeps, the spinal cord never; volition and\nsensation may be suspended, but not reflex action.\u201d This proposition is\nextremely questionable; yet it is indispensable to the reflex theory;\nbecause unless sensation and volition _are_ suspended during sleep, we\nmust admit that they can act, without at the same time calling into\nactivity that degree of sensibility which is supposed to constitute\nconsciousness. The child moves in his sleep, defends himself in his\nsleep; but he is not \u201caware\u201d of it.\n\n\u201cChildren,\u201d says Pfl\u00fcger, \u201csleep more soundly than adults, and seem\nto be more sensitive in sleep. I tickled the right nostril of a\nthree-year-old boy. He at once raised his right hand to push me away,\nand then rubbed the place. When I tickled the left nostril he raised\nthe left hand. I then softly drew both arms down, and laid them close\nto the body, embedding the left arm in the clothes, and placing on it a\npillow, by gentle pressure on which I could keep the arm down without\nawakening him. Having done this I tickled his left nostril. He at once\nbegan to move the imprisoned arm, but could not reach his face with\nit, because I held it firmly though gently down. He now drew his head\naside, and I continued tickling, whereupon he raised the _right_ hand,\nand with it rubbed the _left_ nostril--an action he never performed\nwhen the left hand was free.\u201d\n\n17. This simple but ingenious experiment establishes one important\npoint, namely, that the so-called reflex actions observed in sleep\nare determined by sensation and volition. The sleeping child behaves\nexactly as the waking child behaved; the only difference being in\nthe energy and rapidity of the actions. If the waking child felt and\nwilled, surely the sleeping child, when it performed precisely similar\nactions, cannot be said to have felt nothing, willed nothing? It is\nnot at one moment a sentient organism, and at the next an insentient\nmechanism.\n\nIt is possible to meet this case by assuming that the child was nearly\nawake, and that a dim consciousness was aroused by the tickling, so\nthat the cerebral activity was in fact awakened. But, plausible as\nthis explanation may be (and I am the more ready to admit it because I\nbelieve the brain always co-operates when it is present), it altogether\nfails when we come to experiments on decapitated animals. If any one\nwill institute a series of such experiments, taking care to compare the\nactions of the animal before and after decapitation, he will perceive\nthat there is no more difference between them than between those of the\nsleeping and the waking child.\n\n18. Even more striking is the following experiment, devised by Pfl\u00fcger,\nwhich I have verified, and varied, many times: A frog is decapitated,\nor its brain is removed.[236] When it has recovered from the effect of\nthe ether, and manifests lively sensibility, we place it on its back,\nand touch, with acetic acid, the skin of its thigh just above the\n_condylus internus femoris_. (Let the reader imagine his own shoulder\nburnt at the point where it can be reached with the thumb of the same\narm, and he will realize the operation.) No sooner does the acid begin\nto burn than the frog stretches out the _other_ leg, so that its body\nis somewhat drawn towards it. The leg that has been burnt is now bent,\nand the back of the foot is applied to the spot, rubbing the acid\naway--just as your thumb might rub your shoulder. This is very like\nthe action of the tickled child, who always uses the right hand to rub\nthe right cheek, unless it be held; but when the child\u2019s right hand is\nprevented from rubbing, the left will be employed; and precisely this\ndo we observe with the brainless frog: prevent it from using its right\nleg, and it will use its left!\n\nThis has been proved by decapitating another frog, and cutting off\nthe foot of the leg which is to be irritated. No sooner is the acid\napplied, than the leg is bent as before, and the stump is moved to and\nfro, as if to rub away the acid. But the acid is not rubbed away, and\nthe animal becomes restless, as if trying to hit upon some other plan\nfor freeing himself of the irritation. And it is worthy of remark that\nhe often hits upon plans very similar to those which an intelligent\nhuman being adopts under similar circumstances. Thus, the irritation\ncontinuing, he will sometimes cease the vain efforts with his stump,\nand stretching that leg straight out, bends the _other_ leg over\ntowards the irritated spot, and rubs the acid away. But, to show how\nfar this action is from one of \u201cmere mechanism,\u201d how far it is from\nbeing a direct reflex of an impression on a group of muscles, the\nfrog does not _always_ hit even on this plan. Sometimes it bends its\nirritated leg more energetically, and likewise bends the body towards\nit, so as to permit the spot to be rubbed against the flank--just as\nthe child, when both his hands are held, will bend his cheek towards\nhis shoulder and rub it there.\n\n19. It is difficult to resist such evidence as is here manifested. The\nbrainless frog \u201cchooses\u201d a new plan when the old one fails, just as\nthe waking child chooses. And an illustration of how sensations guide\nand determine movements, may be seen in another observation of the\nbrainless frog, when, as often happens, it does not hit upon either of\nthe plans just mentioned, but remains apparently restless and helpless;\nif under these circumstances we perform a part of the action for it,\n_it will complete what we have begun_: if we rub the irritated leg, at\nsome distance from the spot where the acid is, with the foot of the\nother, the frog suddenly avails itself of this _guiding sensation_, and\nat once directs its foot to the irritated spot.\n\nIn these experiments on the triton and the frog, the evidence of\nsensation and volition is all the stronger, because the reactions\nproduced by irritations are not uniform. If when a decapitated animal\nwere stimulated it always reacted in _precisely the same way_, and\nnever chose _new means_ on the failure of the old, it would be\nconceivable to attribute the results to simple reflex action--i.\u00a0e. the\nmechanical transference of an impulse along a prescribed path. It is\npossible so to conceive the breathing, or the swallowing mechanism: the\nimpression may be directly reflected on certain groups of muscles. But\nI cannot conceive a machine suddenly striking out new methods, when the\nold methods fail. I cannot conceive a machine thrown into disorder when\nits accustomed actions fail, and in this disorder suddenly lighting\nupon an action likely to succeed, and continuing _that_; but I can\nconceive this to be done by an organism, for my own experience and\nobservation of animals assures me that this is always the way new lines\nof action are adopted. And this which is observed of the unmutilated\nanimal, I have just shown to be observed of the brainless animal;\nwherefore the conclusion is, that if ever the frog is sentient, if\never its actions are guided by sensation, they are so when its brain is\nremoved.\n\n20. Schr\u00f6der van der Kolk thinks that Pfl\u00fcger was deceived in\nattributing sensation and volition to the frog, because the reflex\nactions are, he says, so nicely adapted to their ends, that they are\nundistinguishable from voluntary actions. The mechanism is such that,\nby means of the communications established between various groups of\ncells, all these actions adapted to an end may be excited by every\nstimulus. But I deny the fact. I deny that all the actions are awakened\nby every stimulus. Only some few are awakened, and those are not\nalways the same, nor do they follow the same order of succession. One\ndecapitated frog does not behave exactly like another under similar\ncircumstances; does not behave exactly like himself at different\nseasons; unlike a machine, he manifests spontaneity in his actions, and\nvolition in the direction of his actions.\n\n21. The reader will notice that my illustrations show these actions of\nthe brainless animal to have the same external characters as those of\nthe unmutilated animals. I am therefore not here concerned to prove\nthe psychical nature of these actions, unless it be granted that the\nunmutilated animal has sensation and volition. This of course can\nonly be inferred, not proved. But the inference must not be allowed\nin the one case and refused in the other. Young rabbits and puppies\nwhen taken from their mothers manifest discomfort by restless movement\nand whining. Do they feel the discomfort they thus express? If ever\nrabbits and puppies may be said to feel, we must answer, Yes. Well,\nif the brain be removed from rabbits and puppies, precisely similar\nphenomena are observed when these young animals are taken from\ntheir mothers. \u201cI observed the motions, which seemed the result of\ndiscomfort, quickly cease when I warmed the young rabbit by breathing\non it. After a while it was completely at rest, and seemed sunk in\ndeep sleep; occasionally, however, it moved one of its legs without\nany external stimulus having been applied, and this not spasmodically,\nbut in the manner of a sleeping animal.\u201d[237] Is this cessation of\nthe restlessness, when warmth is restored, not evidence of sensation?\nWe see an infant restless, struggling, and squalling; and we believe\nthat it is hungry, or that some other sensations agitate it; it is\nput to the breast, and its squalls subside; or a finger is placed in\nits mouth, and it sucks that, in a peaceful lull, for a few moments,\nto recommence squalling when the finger yields no satisfaction. If we\naccept these as signs of sensation, I do not see how we can deny such\nsensation to the brainless animal which will also cease to cry, and\nwill suck the delusive finger.\n\n22. One of the earliest advocates of the Reflex Theory sums up\nhis observations in these words: \u201cIt is clear that brainless\nanimals, although without sensation, because not endowed with\nmind, nevertheless, by means of external impressions which operate\nincessantly on them, perform all the acts and manifest all the activity\nof the sentient animal; everything that is effected sensationally\nand volitionally, they effect by means of the organic forces of the\nimpressions.\u201d[238] Call Sensibility one of the organic forces, if you\nplease, but so long as the acts performed are not only the same as\nthose of a sentient animal, but are performed by the same mechanism,\nthey have every claim to the character of sensational acts which can be\nurged in the case of these animals when the brain is present. And the\nonly reason on which this claim is disputed is the assumed loss of all\nsensation with the loss of the brain. Here, therefore, lies the central\npoint to be determined.\n\n\n\n\nCHAPTER II.\n\nDEDUCTIONS FROM GENERAL LAWS.\n\n\n23. The evidence is of two kinds: deductions from the general laws of\nnervous action, and inductions from particular manifestations. The\nformer furnish a presumption, the latter a proof.\n\nThe central process which initiates a reflex action may be excited\nby the external stimulation of a peripheral nerve, by the internal\nstimulation of a peripheral nerve, or by the irradiation from some\nother part of the central tissue. The last-named stimulations are\nthe least intelligible, because they are so varied and complex,\nand so remote from observation; among them may be placed, 1\u00b0, the\norganized impulses of Instinct and Habit, with their fixed modes of\nmanifestation; 2\u00b0, the organized impulses of Emotion, which are more\nvariable in their manifestations, because more fluctuating in their\nconditions; 3\u00b0, the organized impulses of Intellect, the most variable\nof all. Whether we shrink on the contact of a cold substance or on\nhearing a sudden sound,--at the sight of a terrible object,--at the\nimaginary vision of the object,--or because we feign the terror which\nis thus expressed,--the reflex mechanism of shrinking is in each case\nthe same, and the neural process discharged on the muscles is the same;\nbut the state of Feeling which originated the change--or, in strictly\nphysiological terms, the inciting neural process which preceded this\nreflex neural process--was in each case somewhat different, yet in each\ncase was a mode of Sensibility.\n\n24. The property of Sensibility belongs to the whole central tissue;\nand we have every reason to believe that unless it is excited no reflex\ntakes place, whereas when it is exaggerated--as in epilepsy, or under\nstrychnine--the reflex discharges are convulsive. When an\u00e6sthetics are\ngiven, consciousness first disappears, and then reflexion. When the\nsensorium is powerfully excited by _other_ stimuli, the normal stimulus\nfails to excite either consciousness or reflexion. Hence our conclusion\nis that for consciousness, on the one hand, and _normal_ reflexion, on\nthe other, the proximate condition is a change in the sensorium; or--to\nphrase it more familiarly--Feeling is necessary for reflex action.\n\nThe difficulty in apprehending this lies in the ambiguity of the\nterm Feeling. Many readers who would find no difficulty in admitting\nSensibility as a necessary element in reflex action, will resist the\nidea of identifying Sensibility with Feeling. But this repugnance must\nbe overcome if we are to understand the various modes of Sensibility\nwhich represent Feeling in animals, and its varieties in ourselves. We\nunderstand how the general Sensibility manifests itself in markedly\ndifferent sensations--how that of the optic centre differs from that\nof the auditory centre, and both from a spinal centre. The tones of a\nviolin are not the same as the tones of a violoncello, both differ from\nthe tones of a key-bugle: yet they all come under the same general laws\nof tonality. So, as I often insist, the tissues in brain and cord being\nthe same, their properties must be the same, their laws of excitation,\nirradiation, and combination the same, through all the varieties in\ntheir manifestations due to varieties of innervation. Hence it is\nthat there are reflex cerebral processes no less than reflex spinal\nprocesses: the motor impulse from, the hemispheres on the _corpora\nstriata_, or from posterior gray substance on anterior gray substance,\nis similar to that from the anterior gray substance on the motor\nnerves. The difference in reflexes arises from the terminal organs; as\nthe difference in sensations arises from the surfaces stimulated. But\nnot only are there reflex processes in the brain, of the same _order_\nas those in the cord, there are volitional processes in the cord of\nthe same order as those in the brain. And in both the processes are\nsometimes conscious, sometimes unconscious. No evidence suggests that\nin the conscious action there is a sensorial process, and a purely\nphysical process in the unconscious action--only a different _relation_\nof one sensorial process to others.\n\n25. Let us contrast a cerebral and a spinal process, in respect to the\nthree stages of stimulation, irradiation, and discharge. A luminous\nimpression stimulates my retina, this excites my sensorium, in which\nsecond stage I am conscious of the luminous sensation; the final\ndischarge is a perception, or a mental articulation of the _name_ of\nthe luminous object. But the irradiation may perhaps not have been\nsuch as to cause a _conscious_ sensation, because the requisite neural\nelements were already grouped in some other way; in this case there is\nan unconscious discharge on some motor group, and instead of perceiving\nand naming the luminous object, I move my head, or my band, or my\nwhole body, avoiding the object, or grasping at it. A third issue is\npossible: the irradiation, instead of exciting a definite perception,\nor a definite movement, may be merged in the stream of simultaneous\nexcitations, and thus form the component of a group, and the discharge\nof this group will be a perception or a movement.\n\nIt is the same with a spinal process. An impression on the skin is\nirradiated in the cord, and the response is a movement, of which we\nare conscious, or unconscious. Here also a third issue is possible:\nthe irradiation may be merged in a stream of simultaneous excitations,\nmodifying them and modified by them, thus forming a component in some\nulterior discharge.\n\n26. The obstacle in the way of recognizing that cerebral processes and\nspinal processes are of the same order of sensorial phenomena, and have\nthe same physiological significance when considered irrespective of the\ngroup of organs they call into activity, is similar to the obstacle\nwhich has prevented psychologists from recognizing the identity of the\nlogical process in the combinations of Feeling and the combinations\nof Thought, i.\u00a0e. the Logic of Feeling and the Logic of Signs. This\nobstacle is the fixing attention on the diversity of the effects when\nthe same process operates with different elements. Because the spinal\ncord manifests the phenomena of sensation and volition, we are not to\nconclude that it also manifests ideation and imagination; any more\nthan we are to conclude that a mollusc is capable of musical feelings\nbecause it is affected by sounds.\n\n27. The careless confusion of general properties with special\napplications of those properties, and of functions with properties, has\nbeen a serious hindrance to the right understanding of Sensibility and\nits operations. Instead of recognizing that the nervous system has one\ngeneral mode of reaction, which remains the same under every variety\nof combination with other systems, physiologists commonly lose sight\nof this general property, and fix on one mode of its manifestation as\nthe sole characteristic of Sensibility. Sometimes the mode fixed on\nis Pain, at other times Attention. Thus, when an animal manifests no\nevidence of pain under stimulations which ordinarily excite severe\npain, this is often interpreted as a proof that _all_ sensation is\nabsent; and if with this absence of pain there is--as there often\nis--clear evidence of the presence of some other mode of sensibility,\nthe contradiction is evaded by the assumption that what here looks like\nevidence of sensation is merely mechanical reflexion. One would think\nthat Physiology and Pathology had been silent on the facts of analgesia\nwithout an\u00e6sthesia, and of so much conscious sensation which is\nunaccompanied by pain.[239] Who does not know that a patient will lose\none kind of sensibility while retaining others--cease to feel pain,\nyet feel temperature, or be insensible to touch, yet exquisitely alive\nto pain?[240] Inasmuch as Sensibility depends on the condition of the\ncentres, an abnormal condition will obviously transform the reaction\nof the centres into one very unlike the normal reaction. For example,\nAntoine Cros had a patient who was quite unable to feel the sensation\nof cold on her left side--every cold object touching her skin on that\nside was felt as a very hot one; whereas a hot object produced \u201cthe\nsort of sensation which followed the application of an intermittent\nvoltaic current.\u201d[241] Thus also the experiments of Rose[242] and\nothers have exhibited the effects of a dose of Santonine in causing all\nobjects to be seen as yellow in one stage, and violet in another.\n\n28. If, then, certain alterations in the organic conditions are\naccompanied by a suppression or perversion of some modes of\nSensibility, without suppressing the rest, it is but rational to\nsuppose that profound disturbances of the organic mechanism, such\nas must result from the removal of the brain, will also suppress or\npervert several modes of Sensibility, and yet leave intact those\nmodes which belong to the intact parts of the mechanism. Assuming\nthat the spinal centres with the organs they innervate are capable of\nreacting under certain modes of sensation, these will not necessarily\nbe suppressed by removal of the brain--all that will thereby be\nsuppressed is their co-operation with the brain. I know it will be\nsaid that precisely this co-operation is necessary for sensation; and\nthat the spinal reactions are simple reflexions in which sensation has\nno part. This, however, is the position I hope to turn. Meanwhile my\nassumption is that sensation necessarily plays a part in the reflex\nactions _of the organism_, and when that organism is truncated, its\nactions are proportionately limited, its sensations less complex. The\nspinal cord, separated from encephalic connections, cannot react in the\nspecial forms of Sensation known as color, scent, taste, sound, etc.,\nbecause it does not innervate the organs of these special senses, nor\nco-operate with their centres. But it can, and does, react in other\nmodes: it innervates skin and muscles; and the sensibilities, thus\nexcited, it can also _combine_ and _co-ordinate_. It has its Memory,\nand its Logic, just as the brain has: both no longer than they are\nintegral parts of an active living organism: neither when the organism\nis inactive or dead. We do not expect the retina to respond in sounds,\nnor the ear to respond in colors: we expect each organ to have its\nspecial mode of reaction. What is common to both is Sensibility.\nWhat is common to brain and cord is Sensibility--and the laws of\nGrouping. Instead of marvelling at the disappearance of so many modes\nof Sensibility when the brain is removed, our surprise should be to\nfind so many evidences of Sensibility remaining after so profound a\nmutilation of the mechanism.\n\n29. The current hypothesis, which assumes that the brain is the sole\norgan of the mind, the sole seat of sensation, is a remnant of the\nancient hypothesis respecting the Soul and its seat; and on the whole\nI think the ancient hypothesis is the more rational of the two. If the\nSoul inhabits the organism, using it as an instrument, playing on its\norgans as a musician plays on his instrument, we are not called upon\nto explain the mode of operation of this mysterious agent; but if the\nSoul be the subjective side of the Life, the spiritual aspect of the\nmaterial organism, then since it is a synthesis of all the organic\nforces, the consensus of all the sentient phenomena, no one part can\nusurp the prerogatives of all, but all are requisite for each. And\nthis indeed is what few physiologists would nowadays dispute. In spite\nof their localizing sensation in the cerebral cells, they would not\nmaintain that the cerebral cells, nor even the whole brain, could\nproduce sensation--if _detached_ from the organism; the cheek of the\nguillotined victim may have blushed when struck, but who believes that\nthe brain felt the insult, or the blow? Obviously, therefore, when we\nread that thought is \u201ca property of the gray substance of the brain, as\ngravitation is of matter,\u201d or that the brain is the exclusive organ of\nSensation, the writers cannot consistently carry out their hypothesis\nunless they silently reintroduce other organs as co-operating agents;\nfor a neural process in the cerebrum is _in itself_ no more a\nsensation than it is a muscular contraction, or a glandular secretion:\nthe muscles must co-operate for the contraction, the gland for the\nsecretion, the neural process being simply the exciting cause. In\nlike manner the Sensorium is necessary for the sensation, the neural\nprocess--in cerebrum, or elsewhere--being simply the exciting cause.\n\n30. And what is the Sensorium? A long chapter would be required\nto state the various opinions which have been held respecting its\n_seat_, although amid all the disputes as to the organ, there has been\nunanimity as to the function, which is that of converting stimulations\ninto sensations. I cannot pause here to examine the contending\narguments, but must content myself with expounding the opinion I hold,\nnamely, that the Sensorium is the _whole_ of the sensitive organism,\nand not any one isolated portion of it. When light falls on the optic\norgan, or air pulses on the auditory organ, the reaction of each organ\ndetermines the _specific_ character of the sensation, _but no such\nsensation is possible unless there be a reaction of the organism_;\nand the nature of the product will of course vary with the varying\nfactors which co-operate--a simple organism, a truncated organism, an\nexhausted or otherwise occupied organism, will react differently from\na complex, a normal, or an unoccupied organism. Detach the optic organ\nwith its centre from the rest of the organism, and no normal sensation\nof Sight will result from its stimulation; and in a lesser degree this\nis equally true of a stimulation of the optic organ when the sensorium\nis exhausted, or powerfully affected by other stimuli. Because of the\ngreat importance of the cerebrum, and its predominance in the nervous\nsystem, it has been supposed to constitute the whole of the sensorium,\nin spite of the evidence of varied Sensibility after the cerebrum has\nbeen removed. I do not wish to understate the cerebral importance (see\np. 166), yet I must say that the modern phrase _cerebration_, when\nemployed as more than a shorthand expression of the complex processes\nwhich a cerebral process initiates, and when taken as the objective\nequivalent of Consciousness or of Thought, seems to me not more\njustifiable than to speak of Combustion as the equivalent of Railway\nTransport. The railway wagons will not move unless the fuel which\nsupplies the boiler be ignited; the organism will not think unless the\ncerebrum excites this peculiar mode of Sensibility by its action on\nthe organs. _It is the man, and not the brain, that thinks_: it is the\norganism as a whole, and not one organ, that feels and acts.\n\n31. Consciousness, or Sensation, is a complex product not to be\nrecognized in any _one_ of its factors. Cerebral processes and spinal\nprocesses are the elements we analytically separate, as muscular\ncontractions are the elements of limb-movements. The synthetic unity\nof these elements is a reflex; this we analytically decompose into\na sensation and a movement; and then we speak of sensation as the\nreaction of the sensory organ, the movement as the reaction of the\nmuscular organ. By a similar procedure we separate the stimulation of\na sensory nerve from the reaction of the sensory organ, and that from\nthe reaction of the sensorium; and in this way we may come to regard\nCerebration as Thought. But those who employ this artifice should\nremember that the organism is not an assemblage of organs, made up of\nparts put together like a machine. The organs are differentiations of\nthe organism, each evolved from those which preceded it, all sharing in\na common activity, all _inter_-dependent.\n\n32. That co-operation of the Personality which is conspicuous in\nconscious actions is also inductively to be inferred in sub-conscious\nand unconscious actions. We know that a man reacts on an impression\naccording to his physical and mental state at the moment--that through\nhis individuality he feels differently, and thinks differently from\nother men, and from himself at other epochs, and in other states.\nBecause he resembles other men in many and essential points we\nconclude that he will resemble them in all; but observation proves\nthis conclusion to be precipitate. Other men see a blue color in the\nsky, or feel awe at sight of the setting sun; but he has perhaps\nnot learned to discriminate this sensation, is not conscious of the\nblue; nor has he learned to feel awe at the setting sun. Why--having\nnormally constructed eyes--does he not see the blue of the sky? For the\nsame reason that a dog, or an infant, fails to see it. The color has\nno _interest_ for him (and all cognition is primarily emotion), nor\nhas this want of personal interest been rectified from an impersonal\nsource: he has never been taught to distinguish the color of the sky;\nand his eye wanders over it with the indifferent gaze with which a\nsavage would regard a Greek codex.\n\n33. The point here insisted on, namely, that every reaction on an\nimpression is indirectly the reaction of the whole organism, and that\nno organ detached from the organism has more significance than a word\ndetached from a sentence, is of far-reaching importance, and peculiarly\nworthy of attention in considering the Reflex Theory, because almost\nall the evidence urged in support of that theory presupposes the\nlegitimacy of concluding what takes place in the organism from what\nis observed in an organ detached from its normal connections. No\nexperimental proof is necessary to show that many actions take place\nunconsciously; the fact is undisputed. But does unconsciously mean\ninsentiently? It is certain that the unconscious actions take place in\na sentient organism, and involve organic processes of the same _order_\nas the actions which are conscious. It is also certain that many\nsentient processes take place unconsciously. For thousands of years men\nused their eyes, and saw as their descendants see, yet were unconscious\nof the blue sky and green of the grass. Were their visual reactions\nnot of the same _order_ as our own? So far as the optic apparatus\nis concerned, there cannot be a doubt on the point; yet in them the\nsensorium having a somewhat different disposition--the neural elements\nbeing differently combined--their reactions correspondingly differed.\nThey too had optical Sensibility, and visual sensations; but they did\nnot feel precisely what we feel.\n\n34. I have chosen these somewhat remote illustrations for the sake of\ntheir psychological interest; but I might have confined myself to more\nfamiliar examples. Thus the contents of the consciousness of a man born\nblind cannot be _the same_ as the contents of one who has had visual\nexperiences, which will enter into the complex of every conscious\nstate, because the visual organs will have affected his sensorium;\nnevertheless in the organism of the blind man there are conditions\nso similar to those of other men, and his experiences will have been\nso similar, that in spite of the modifications due to the absence of\nvisual experiences, his consciousness will in the main resemble theirs.\nBut now let us in imagination pursue this kind of modification, let us\ntake away hearing, taste, and smell, and we shall have proportionately\nsimplified the contents of consciousness--the reactions of the\nsensorium--in thus simplifying the organism. There still will remain\nTouch, Temperature, Pain, and the Systemic Sensations. There will still\nremain an organism to react on impressions. So long as there is a\nliving organism, however truncated, there is a sentient mechanism. When\nthe brain has been removed, the removal causes both a _disturbance_ of\nfunction and a _loss_ of function; the mechanism has been seriously\ninterfered with; yet all those parts of the mechanism which still\nco-operate manifest their physiological aptitudes. The animal can live\nwithout its brain, _ergo_ it can feel without its brain. Observation\nproves this, for it discovers the brainless animal manifesting various\nsensibilities, and combining various movements. The vision of the\nbrainless animal is greatly impaired, but it nevertheless persists.\nThe intelligence is greatly impaired, the spontaneity is reduced to a\nminimum; but still both intelligence and spontaneity are manifested.\n\n35. The physiologist has only two conclusions open to him. Either\nhe holds Sensation to be a _property_ of nerve-tissue--and in that\ncase he must assign it to the spinal cord as to the brain; or else\nhe holds Sensation to be a _function_ of an organ--and in that case,\nalthough analytically he may decompose the organism into separate\norgans, assigning special sensations to the reactions of each, he must\nstill admit that in reality these organs only yield sensations as\ncomponent parts of the organism. The notion of a separate organ, such\nas the brain, being the exclusive seat of sensation is thus seen to be\nuntenable.\n\nIn popular phrase, \u201cit is not the eye which sees, but the mind behind\nthe eye.\u201d It is not the stimulus which is the _object_ felt--it is the\nchange in consciousness--the reaction of the sensorium. No one would\npropound the absurdity that the retinal cells _see_, or the auditory\ncells _hear_ (although by a conventional ellipsis these cells are said\nto be \u201cpercipient\u201d of colors and sounds), yet many writers have no\nhesitation in asserting that the cerebral cells are the seats of these\nand all other sensations. In a hundred treatises may be read the most\nprecise description of the transformation of molecular changes in the\nretinal cells into molecular changes in the cerebral cells, where, it\nis said, \u201cwe know that the stimulations become sensations.\u201d Now who\nknows this? How can it be known? Nay, who, on reflection, fails to see\nthat this cannot be so? If a sensation of sight were not much _more_\nthan a molecular change in the cerebrum stimulated by a molecular\nchange in the optic tract, three conclusions would follow, each of\nwhich is demonstrably erroneous:--\n\nI. The cerebrum in a decapitated animal would respond by a sensation of\nsight to a retinal stimulation.\n\nII. The animal deprived of its cerebrum could not respond by a\nsensation of sight to a retinal stimulation.\n\nIII. The same retinal stimulation would always produce the same\ncerebral process and the same sensation; whereas the sensation depends\non the condition of the sensorium at the time.\n\n36. The difference between the Reflex Theory and that here upheld is\nimportant in its general relations, and yet turns on a point which may\neasily appear insignificant. The Reflex Theory asserts that when a\nsensory nerve is stimulated, the excitation of the centre may either\nsubdivide into two waves, one of which passes directly to the brain\nand there awakens sensation, the other passes over to the motor-roots\nand causes muscular contractions; or, instead of thus subdividing, the\nwave may pass at once to the motor-nerves, and then there is movement\nwithout sensation. This is obviously a restatement in anatomical terms\nof the observed fact that some reflexes take place consciously and\nsome unconsciously. But what evidence is there for this anatomical\nstatement? We have seen that there is none. According to all we\nactually know, and reasonably infer, the continuity of tissue and the\nirradiation of excitation are such that the stimulus wave must always\naffect the whole system, so that brain and cord being structurally\nunited, their reactions must co-operate with varying energy dependent\non their statical conditions at the time.[243]\n\n37. The physiological fact that the irradiation is _restricted_ to\ncertain paths, and therefore only certain portions of the whole system\nare excited to discharge--the fact that stimulation takes effect along\nthe lines of least resistance--is that which gives the Reflex Theory\nits plausible aspect. But this fact of restriction is not dependent on\nan _anatomical_ disposition of structure, it is, as we have already\nseen (PROBLEM II. \u00a7 166), dependent on a fluctuating physiological\ndisposition--a temporary statical condition of the centres. And it\nenables us to understand why the reflex action which is at one moment\na distinctly conscious or even a volitional action, is at another\nsub-conscious or unconscious. When an object is placed in the hand of\nan infant the fingers close over it by a simple reflex. This having\nalso been observed in the case of an infant born without a brain,[244]\none might interpret it as normally taking place without brain\nco-operation, were there not good grounds for concluding that normally\nthe brain must co-operate. Thus if the object be placed in the hand of\na boy, or a man, the fingers will close, or not close--not according to\nan anatomical mechanism, but according to a physiological condition:\nif the attention preoccupy his sensorium elsewhere, his fingers will\nprobably close, probably not; if his sensorium be directed towards the\nobject, either by the urgency of the sensitive impression, or by some\none\u2019s pointing to the object, the fingers will close or not close,\njust as he chooses--perhaps the hand will be suddenly drawn away. The\ncentre of innervation for the fingers is in the cord, and from this\ncomes the final discharge of the sensitive stimulation; but the neural\nprocesses which preceded this discharge, and were consequent on the\nstimulation, were in each case somewhat different. In each case the\nimpression on the skin was carried to the cord, and thence irradiated\nthroughout the continuous neural axis, restricted to certain paths by\nthe resistance it met with, but blending with waves of simultaneous\nexcitations from other sources, the final discharge being the resultant\nof these component forces. We may suppose the brain to be the seat\nof consciousness, and yet not conclude that the brain was unaffected\nbecause the fingers closed unconsciously; any more than we conclude\nthat the retina of the unoccupied eye is unaffected by light when with\nthe other we are looking through a microscope, and only _see_ objects\nwith this eye--though directly we attend to the impressions on the\nother eye we see the objects which before were unseen. We know that the\nmuscles of the back are all involved in walking, standing, etc., but we\nare seldom conscious of their co-operation till rheumatism or lumbago\nmakes us painfully alive to it.\n\n38. The two main positions of the Reflex Theory are, 1\u00b0, that\nreflex actions take place without brain co-operation,--as proved by\nobservation of decapitated animals; 2\u00b0, that they take place without\nbrain co-operation,--as proved by our being unconscious of them.\n\nTo these the answers are: 1\u00b0. The proof drawn from observation of\ndecapitated animals is defective, because the conditions of the\norganism are then abnormal--there is a disturbance of the mechanism,\nand a loss of some of its components. The fact that a reflex occurs\nin the absence of the brain is no proof that reflexes when the brain\nis present occur without its participation. 2\u00b0. The absence of\nconsciousness cannot be accepted as proof of the brain not being in\naction, because much brain-work is known to pass unconsciously, and\nthere are cerebral reflexes which have the same characters as spinal\nreflexes.\n\n39. A prick on the great toe traverses the whole length of the spinal\naxis with effects manifested in various organs--the muscles of the\nlimb, the heart, the chest, the eyes, etc. The leg is withdrawn,\nthe heart momently arrested, the eyes turned towards the source of\nirritation, the thoughts directed towards relief. These effects can\nbe observed--there are others which lie beyond our observation, and\ncan only be revealed by delicate experimental tests. But even the\nobservable effects are very fluctuating, because they depend on\nfluctuating conditions. All we can say is, that so long as there is\ncontinuity of structure, there must be continuity of excitation;\nand the brain structurally connected with the centre of a sensory\nimpression, must necessarily co-operate more or less in the reactions\nof that centre. In other words, the brain, although not the exclusive\nseat of sensation, plays a part in every particular sensation, so long\nas it forms a part of the stimulated organism.\n\n40. This view being so widely opposed to the views current in\nphysiological schools, I was gratified to find Dr. Crichton Browne led\nby his researches to a conclusion not unlike it in essential features.\nIn his essay on the Functions of the Optic Thalami[245] (well worthy\nof attention on other grounds) he says: \u201cAllowing the spinal cord a\npower of independent action, it may still be that it generally acts\nreflexly through, or in association with, a superior centre. The\nsensorial ganglia can undoubtedly act alone in a reflex manner, but\nthey almost invariably consult the cerebrum before dealing with the\nimpressions which they receive; so it may be that the spinal cord,\nthough capable of spontaneous reaction, may yet commonly refer to some\nhigher seat of compound co-ordination before sending forth an answer\nto any message brought to it.\u201d What is here stated as a possible and\noccasional process, I consider to be a necessary and universal process.\nDr. Browne acutely remarks that if \u201cwhat may be termed the encephalic\nloop were an integral part of every reflex act, then the influence of\nan intracranial lesion in checking reflex action would not be difficult\nto understand\u201d--and we may add the notorious influence of the brain in\narresting reflex actions, and modifying them by the will, which is only\nexplicable on the supposition that the cerebral and spinal centres are\nfunctionally associated. Dr. Browne further remarks: \u201cIn experimenting\nupon myself I have sometimes thought that when the toe is pricked the\nsensation of pain actually precedes the movement of withdrawal; and\nin experimenting upon patients with sluggish nervous systems I have\ncertainly noticed that after the pricking of the toe the little cry of\npain has anticipated the muscular contractions of the leg. Now this cry\nof pain is a secondary reflex act through the sensorial centre; it is\nthe result of a discharge from efferent nerves from the summit of what\nwe have spoken of as the encephalic loop line; and we should certainly\nnot expect that it would be developed earlier than the primary\nreflexion upon the motor apparatus, unless indeed what we have regarded\nas the primary reflexion really itself took place by way of the loop\nline.\u201d\n\n41. The difference between a voluntary and involuntary act is not, I\nconceive, that in the one case the brain co-operates and in the other\nis inactive, but that while in both the brain co-operates, the state\nof the sensorium known as mental prevision or ideal stimulation, is\npresent in the one, and absent or less conspicuous in the other. So\nlikewise the difference between a normal reflex action accompanied, and\nthe same action unaccompanied by consciousness, is not that the brain\nco-operates in the one and is inactive in the other, but that the state\nof the sensorium is somewhat different in the two cases. Movements\nwhich originally were voluntary and difficult of execution--accompanied\ntherefore by brain co-operation--become by frequent repetition\nautomatic, easy of execution, and unconscious--they are then said to\ndepend on the direct action of the established mechanism. Granted. But\nwhat are the components of this mechanism? Are they not just those\ncentres and organs which at first effected the movements? In becoming\neasy and automatic, the movements do not _change their mechanism_--the\nmoving organs and the motor conditions remain what they were; all that\nis changed is the degree of consciousness, i.\u00a0e. the _state_ of the\nsensorium which precedes and succeeds the movement. It is this which\nconstitutes the difficulty of the question. Some readers may consider\nthat all is conceded when unconsciousness is admitted. But this is\nnot so. My present argument is the physiological one that the brain\nco-operates in reflex actions whenever the brain is structurally united\nwith the reflex centres; the psychological question as to whether\nconsciousness is also involved in this brain co-operation must be\ndebated on other grounds; and we have already seen that consciousness\noperates in gradations of infinite delicacy.\n\nObserve a man performing some automatic action, such as planing a\ndeal board, or cutting out a pattern, which he has done so often that\nhe is now able to do it \u201cmechanically.\u201d It is certain that his brain\nco-operates, and that he could not act thus with an injured brain;\nyet he is said to act unconsciously, his brain occupied elsewhere as\nhe whistles, talks to bystanders, or thinks of his wife and children.\nYet the brain is acting as an overseer of his work, attentive to every\nstroke of the plane, every snip of the scissors; and this becomes\nevident directly his attention is otherwise absorbed by an interesting\nquestion addressed to him, or an interesting object meeting his eye:\nthen the work pauses, his hands are arrested, and the automatic action\nwill only be resumed when his attention is released--when he has\nanswered your question, or satisfied himself about the object.\n\n42. This is a step towards understanding the co-operation of the brain\neven in those connate reflexes which were not originally voluntary\nacts, but were from the first organized tendencies, and are capable\nof being realized in the absence of the brain. I admit that it is\ndifficult to find proof of brain co-operation here, though I think\nthe anatomical and physiological evidence render it highly probable.\nBut distinct proof to the contrary would not suffice for the Reflex\nTheory--would not prove that reflex actions were insentient--unless\nthere had previously been proved that which seems to me contradicted\nby the clearest and most massive evidence, namely, that the brain is\nthe sole seat of sentience. This contradictory evidence we will now\nfurnish.\n\n\n\n\nCHAPTER III.\n\nINDUCTIONS FROM PARTICULAR OBSERVATIONS.\n\n\n43. In the last chapter we surveyed the deductive evidence, from which\nthe conclusion was that Reflexion necessarily involves Sensibility,\nbut not necessarily any one particular _mode_ of Sensibility, such\nas Consciousness, Pain, Discomfort, Attention, or the reaction of\nany one of the special Senses. Although each or all of these modes\nmay be involved in the sensorial process which determines a reflex\nact, each or all may be absent. Such is the fact of observation. This\nfact is interpreted on the hypothesis that Reflexion is the exclusive\nproperty of the spinal cord, as Sensation is of the brain. When we\ncome to examine the evidence for this hypothesis, we find it to move\nin a circle: the brain is said to be the exclusive seat of sensation,\nbecause reflex actions can be effected after its removal; and reflex\nactions are said to be insentient because they take place in the\nabsence of the brain.\n\nA gentleman was one day stoutly asserting that there were no\ngold-fields except in Mexico and Peru. A nugget, dug up in California,\nwas presented to him, as evidence against his positive assertion.\nHe was not in the least disconcerted. \u201cThis metal, sir, is, I own,\nextremely _like_ gold; and you tell me that it passes as such in the\nmarket, having been declared by the assayers to be undistinguishable\nfrom the precious metal. All this I will not dispute. Nevertheless,\nthe metal is not gold, but _auruminium_; it cannot be gold, _because_\ngold comes only from Mexico and Peru.\u201d In vain was he informed that\nthe geological formation was similar in California and Peru, and the\nmetals similar; he had fixed in his mind the conclusion that gold\nexisted _only_ in Mexico and Peru: this was a law of nature; he had no\nreasons to give why it should be so; but such had been the admitted\nfact for many years, and from it he would not swerve. He was not fond\nof new-fangled notions, which, after all, would only lead us back to\nthe exploded errors of the past. To accept the statement that gold was\nto be found elsewhere than in Mexico and Peru, would be to return to\nthe opinion of the ancients, who thought there was gold in the upper\nregions of Tartary!\n\nSensation is not tangible, assayable, like gold. We can understand,\ntherefore, that the very men who would make merry with the\n_auruminium_, would accept easily such a phrase as \u201creflex action.\u201d\nThe decapitated animal defends itself against injury, gets out of\nthe way of annoyances, cleans itself, performs many of its ordinary\nactions, but is said to do these things without that Sensibility which,\nif its head were on, would guide them. Even before the Reflex Theory\nwas invented this line of argument was used. Gall, referring to the\nexperiments of Sue, previously noticed, says that \u201cSue confounds the\neffects of Irritability with those of Sensibility.\u201d[246] Not gold, dear\nsir, but _auruminium_!\n\n44. On investigating the phenomena we soon come upon two classes which\nmust cause hesitation. We find that the brain has its reflex processes,\nof the same order as those of the cord; we find that these processes\nmay be conscious or unconscious, voluntary or involuntary; so that we\ncan no longer separate brain from cord on the ground of Reflexion. In\nthis respect, at least, the two are mechanisms with similar powers.\nTurning now to the other class of phenomena, we find that precisely as\nthe brain is an organ of Reflexion, the cord is an organ of Sensation.\nAll the evidence we can have, from which to infer the presence of\nsensation, is furnished by the sensorial processes in the cord. Remove\nthe brain, and the animal still manifests Sensibility, and this in\ndegrees of energy and complexity proportional to the mechanisms still\nintact: some of these manifestations have the character of volitional\nactions, some of automatic actions, some of Memory, Judgment, and\nselective Adaptation. These we observe not indeed with the energy and\nvariety of such manifestations when the brain co-operates, since the\ndisturbance of the organism which is the consequence of the brain\u2019s\nremoval--or the meagreness of the organism which is the correlative\nof the brain never having been developed--must of course involve a\ncorresponding difference in the observed phenomena; but the point here\nbrought forward is that phenomena of the same _order_ are manifested by\norganisms with or without a brain.\n\n45. Let us go seriatim through the evidence of these two classes:--\n\n\nCEREBRAL REFLEXES.\n\nWhile Theory separated the actions of the cord from those of the brain\non the ground of their being at times unconscious and involuntary,\nObservation disclosed that this distinction could not be maintained.\n\nThis step was taken by Dr. Laycock in 1840. In a striking paper[247]\nread by him at the British Association in 1844, he brought together the\nevidence on which his view was founded. The idea has been adopted and\nillustrated in the writings of Dr. Carpenter, who now calls the action\n\u201cunconscious cerebration.\u201d\n\n\u201cI was led to this opinion,\u201d Dr. Laycock says in announcing his view,\n\u201cby the general principle that the ganglia within the cranium, being\na continuation of the spinal cord, must necessarily be regulated as\nto their reaction on external agencies by laws identical with those\ngoverning the spinal ganglia and their analogues in the lower animals.\nIf, therefore, the spinal cord is a centre of reflexion, the brain must\nalso be one.\u201d It is a matter of regret that Dr. Laycock did not extend\nthis principle, and declare that whatever was true of the _properties_\nof the cranial centres must also be true of the spinal centres; if the\nbrain have Sensibility, the spinal cord must also have it.\n\nDr. Laycock refers to the curious phenomena of Hydrophobia in proof\nthat reflex actions may be excited by the optic nerves, or by a mere\nidea of water. When a mirror was presented to a patient, the reflexion\nof the light acting on his retina, in the manner of a reflexion\nfrom the surface of water, produced a convulsive sobbing, as in the\nattempt to swallow water, and the patient turned aside his head with\nexpressions of terror. Money was given him to induce him to look a\nsecond time, but before he had looked a minute the same effect was\nproduced.\n\nThe _idea_ of water excited similar convulsions. No sooner was it\nsuggested that the patient should swallow a little water than he seemed\nfrightened, and began to cry out. By kindly encouragements he was\nbrought to express his willingness to drink, but the _sound_ of the\nwater, as it was poured out again, brought on convulsions. In another\ncase, \u201con our proposing to him to drink, he started up, and recovered\nhis breath by a deep convulsive inspiration. On being urged to try,\nhe took a cup of water in one hand and a spoon in the other. With as\nexpression of terror, yet with great resolution, he filled the spoon\nand proceeded to carry it to his lips; but before it reached his mouth\nhis courage forsook him, and he was forced to desist. He repeatedly\nrenewed the attempt, but with no more success. His arm became rigid and\nimmovable whenever he tried to raise it to his mouth, and he struggled\nin vain against this spasmodic resistance.\u201d\n\nIn 1843 Griesinger--who appears to have known nothing of Dr. Laycock\u2019s\npaper--published his remarkably suggestive memoir on Psychical\nReflexes,[248] in which he extends the principle of Reflexion to all\nthe cerebro-spinal centres. The whole course of subsequent research\nhas confirmed this view; so that we may say with Landry, \u201cL\u2019existence\ndu pouvoir r\u00e9flexe dans l\u2019enc\u00e9phale ou dans quelques unes de ses\nparties \u00e9tablit une nouvelle analogie entre le centre nerveux cranien\net la moelle \u00e9pini\u00e8re.\u201d[249] Indeed we have only to consider the\nLaughter which follows a ludicrous idea, or the Terror which follows\na suggestion of danger,--the varying and involuntary expression of\nEmotion,--and the curious phenomena of Imitation and Contagion,--to see\nhow large a place cerebral reflexion occupies.\n\n46. The existence of cerebral reflexion having been thus made manifest,\nDr. Carpenter classed all reflex actions under three heads: 1\u00b0, the\nexcito-motor, determined by the spinal cord; 2\u00b0, the sensori-motor,\ndetermined by the ganglia at the base of the brain; 3\u00b0, ideo-motor,\ndetermined by the brain. From all these Consciousness is absent. From\nthe first, he supposes Sensation to be absent. As an artifice, such\na classification may have its value, but it is physiologically and\npsychologically misleading. It sustains the hypothesis of an imaginary\nexcito-motor mechanism. It restricts Sensibility to one of its many\nmodes. It fails altogether to connect Sensation with Thought, the Logic\nof Feeling with the Logic of Signs.\n\n47. The view of Sensibility as common to the whole cerebro-spinal axis\nis by no means new. Robert Whytt maintained it. Prochaska held that\nthe spinal cord formed the greater part of the _sensorium commune_;\nand he adduced, in proof, the familiar facts of sensibility manifested\nby headless animals. The next writer whom I can discover to have\nheld this opinion is J. J. Sue,--the father of the celebrated French\nromance-writer,--who, in 1803, conceived that his experiments proved\nthe spinal cord to be capable of replacing, to a certain extent, the\nfunctions of the brain.[250] Next came Legallois,[251] who undertook\nto show, by a series of experiments, that the principle of sensation\nand movement, in the trunk and extremities, has its seat in the spinal\ncord. The mere division of the cord, he said, produces \u201cthe astonishing\nresult of an animal, in which the head and the body enjoy separate\nvitality, the head living as if the body did not exist, and the body\nliving as if the head did not exist. Guinea-pigs, after decapitation,\nseem very sensitive to the pain caused by the wound in the neck; they\nalternately carry first one hind-leg and then the other, to the spot,\nas if to scratch it. Kittens also do the same.\u201d\n\nA few years afterwards, 1817, Dr. Wilson Philip concluded that \u201cthe\nspinal marrow possesses sensorial power, as appears from very simple\nexperiments\u201d; but he held the brain to be the _chief_ source of\nsensorial power.[252] The following year, Lallemand supported this\nopinion by the very curious phenomena exhibited by infants born without\nbrains: these infants breathed, swallowed, sucked, squalled, and gave\nvery unequivocal signs of sensibility. The value of such observations\nconsists in disproving the objection frequently urged against the\nevidence of decapitated animals, namely, that in these animals the\nspinal cord preserves the remains of a sensibility endowed by the brain.\n\nLonget here places an observation recorded by Beyer. A new-born infant,\nwhose brain, during the birth, had been completely extirpated (to save\nthe mother\u2019s life), was wrapped in a towel, and placed in the corner\nof the room, as a lifeless mass. While the surgeon was giving all his\ncare to the mother, he heard with horror a kind of murmur proceeding\nfrom the spot where the body had been placed. In three minutes a\ndistinct _cry_ was heard. The towel was removed, and, to the surprise\nof all, this brainless infant was seen struggling with rapid movement\nof its arms and legs. It cried, and gave other signs of sensibility for\nseveral minutes.[253]\n\nIn 1828 Calmeil arrived at the same conclusion as that reached by\nLegallois, Wilson Philip, and Lallemand. Indeed when, in 1833, the\nReflex Theory appeared, this opinion was so firmly rooted, that\nwe find Mr. Grainger combating it as the established error of the\nday. He takes as much pains to show that physiologists are wrong in\nattributing sensation to the spinal cord, as I am here taking to show\nthat they were right.[254] \u201cIt is, indeed, apparent,\u201d he says, \u201cthat\nthe whole question concerning the truth or falsehood of the theory\nwhich attributes the reflex power to the spinal cord hinges upon the\ncorrectness or incorrectness of the received doctrines respecting the\nseat of sensation and volition; so that until those doctrines are\nproved to be false, it is impossible to establish the hypothesis of Dr.\nHall.\u201d[255]\n\nThe reader is requested to take note of this, because when we come to\nthe evidence which proves the spinal cord to be a centre of sensation,\nwe shall find that the _only_ ground for rejecting that evidence is the\nassumed truth of the Reflex Theory, coupled with the assumption of the\nbrain being the exclusive seat of sensation. Whereas if the evidence\nproves that the spinal cord _is_ a sensational centre, then the Reflex\nTheory is destroyed, and cannot be urged against such evidence.\n\n48. Thus many of the facts which prove the sensational function of\nthe spinal cord were known, and even a vague conception of their real\nsignificance was general, until the Reflex Theory came to explain\nall such facts as the results of mechanical adjustment, and of a new\nnervous principle called \u201cReflexion.\u201d For many years this theory has\nreigned, and met with but little opposition. Yet the true doctrine has\nnot wanted defenders in Germany. Nasse[256] denied that decapitated\nanimals showed no spontaneity; he asserted that they exhibited clear\nsigns of mental activity. Carus sarcastically pointed out that the\n_word_ \u201creflex\u201d was replacing \u201cirritability,\u201d as a key to unlock all\npuzzles; and he took up a position which is very similar to the one\noccupied in these pages, namely, that the spinal cord being formed of\ngray matter as well as of fibres, it must have sensibility and power of\nreacting on nervous stimulus, no less than conductibility; that, in\nfact, it is a centre, and must act like all other nerve-centres.[257]\nJ. W. Arnold opposed the Reflex Theory in a very remarkable little\nwork, in which he vindicates the claim of the spinal cord as a sensory\nand motor centre, although denying to its actions any volitional\ncharacter.[258] This was in 1844. Eleven years elapsed without any\nfurther opposition, when Edward Pfl\u00fcger, in 1853, published his work\non the Sensorial Functions of the spinal cord.[259] In this work he\nrecurred to the old views of Prochaska and Legallois; but although he\nattacked Marshall Hall with merciless severity, he did not point out\nthe fundamental error of the Reflex Theory, which theory he seems to\naccept. Nor did he give his views that philosophical and anatomical\nbasis which could alone render his interpretations acceptable. Added to\nthis, the tone of asperity in which his work was written, created some\nprejudice against him; and thus, while many admitted his facts, they\nrejected his conclusions.[260]\n\nIn 1858 Professor Owen read a paper of mine at the Leeds meeting of\nthe British Association, on \u201cThe spinal cord as a centre of Sensation\nand Volition,\u201d in which a rapid indication of my point of view, and\nan account of some experiments to illustrate it, were given--_not_, I\nbelieve, conclusive to any of the audience. Indeed, the subject was\ntoo vast to be discussed in such a paper; and my object was rather to\nexcite new inquiry, than to make converts to a view which could only be\nembraced after a thorough reinvestigation of the dominant theories.\n\nIn 1859 appeared Schiff\u2019s work;[261] and here we find a large space\nallotted to the discussion of Pfl\u00fcger\u2019s doctrine. Schiff, whose\nimmense experience as an experimentalist, and whose acuteness and\ncaution every one will highly estimate, frankly pronounces in favor\nof the sensational character of spinal actions; but he denies that\nthey are volitional, and objects strongly to the introduction of\nany such idea as that of \u201cpsychical activity.\u201d He thinks it utterly\nuntenable to suppose that impressions have reactions in the brain\nwhich they have not in the spinal cord:--if one has sensibility, the\nother must have it; and he thinks that, so far from the actions of the\ncord being distinguishable from those of the brain by the character\nof \u201creflexion,\u201d and depending on a mechanical arrangement--_all_\nactions, cerebral or spinal, are reflex; _all_ depend on a mechanical\narrangement.[262]\n\nSince that time there has been the remarkable work of Goltz, so\noften cited in these pages,[263] and his subsequent experiments on\ndogs, which (although he does not decisively adopt the views of\nPfl\u00fcger) furnish ample evidence that sensation and volition cannot be\nexclusively localised in the brain.\n\n49. Heubel\u2019s interesting experiments[264] show that a frog may be\nthrown into a state of profound sleep by the withdrawal of all external\nstimulation, and in this state will remain lying on its back for hours.\nNow this position is one so very uncomfortable that, when awake, the\nfrog will not retain it a moment, if free to turn round; and when\nasleep, a prick on the toe, a sudden noise, or a beam of light will\nawaken it, causing it to turn. That is to say, the withdrawal of the\nnormal stimuli so lowers the sensibility of the frog\u2019s nerve-centres,\nthat he does not feel the effects of the unusual position, but feels\nthem directly the centres are stimulated into activity. All this is\nintelligible enough on the supposition of the state of sleep being\ndependent on a lowering of the cerebral activity. But what shall we\nsay on learning that precisely the same phenomena are manifested by a\nbrainless frog? Every one knows that the brainless frog is intolerant\nof lying on its back, and immediately turns round, if placed on it. Yet\nthe brainless frog may be thrown into deep sleep by the same exclusion\nof external stimuli; from which he also will be awakened by a prick,\na noise, or a beam of light; and no sooner is he awakened than he at\nonce turns round. Were the brainless frog incapable of sensation, a\nprick on his toe would cause a simple reflex withdrawal of the leg;\nbut this is not the effect; on the contrary, the stimulus excites the\nwhole spinal cord, and whatever sensation of discomfort may be caused\nby the abnormal position of the limbs in an uninjured awakened frog, is\nexcited in the brainless frog.\n\n50. I need not swell this chapter with examples of Sensibility in\nanimals deprived of the brain; many have already been given, and\nany text-book of Physiology will supply more. No one disputes the\nobservations, only the inference that these manifestations were\nsentient: they are said to have been merely mechanical reflexes. If,\nhowever, we can detect in them _some_ evidence of what all recognize as\npeculiarly characteristic of Mind, the mechanical interpretation will\nbe less plausible.\n\nAt the outset the reader must be warned against exaggerating and\ndistorting the bearing of my remarks, and must not suppose that I\ndisregard the vast differences between the Logic of Signs which\nbelongs to Thought, and the Logic of Feeling which belongs to\nSensation, nor suppose that I look upon the spinal cord as a mental\norgan having the _same_ functions as the brain. All that I wish to\nestablish is the common character of spinal and cerebral processes,\nmodified as each is by the character of the actions initiated by the\nprocess.\n\n51. This premised, let us begin with the evidence of\n\n\nDISCRIMINATION.\n\nAlthough this process is usually regarded as purely psychological, it\nmust obviously have its physiological side; we find it in Sensation as\nin Ideation, and may expect to find it in unconscious as in conscious\nprocesses--in a word, in all sensorial processes whatever. Place a\nbit of marble on your tongue, and it will be touched, but not tasted:\nthe sensations of contact and temperature will excite reflexes, but\nlittle or no reflexes from parotid and salivary glands. A difference in\nsensation has a corresponding difference in reflex action; which may be\nmade evident by removing the tasteless marble, and replacing it by a\npinch of carbonate of lime, i.\u00a0e. the marble in another state reduced\nto a powder: this will excite a sensation of taste, and a secretion\nfrom the glands. In both cases your sentient organism was affected, but\nit reacted differently because the difference of the stimulation was\ndiscriminated: consciously or unconsciously, you _felt_ differently.\nAgain: touch the back of your mouth with your finger, or a feather, and\na convulsive contraction of the gullet responds, followed by vomiting,\nif the excitation be renewed. Yet these same nerves and muscles respond\nby the totally opposite action of swallowing, if instead of the\nstimulation coming from your finger, it come from the pressure of food\nor drink.\n\nAnalogous experiments on animals without their brains yield similar\nresults.[265] The salivary secretion and the ordinary reactions of\nTaste are provoked by sapid substances. Still more conclusive are the\nobservations made on a dog whose spinal cord has been divided, and\nwho therefore according to the reigning ideas is incapable of feeling\nany impression made on parts below the section. A pencil inserted in\nthe rectum causes a reaction of the muscles energetically resisting\nthe entrance of this foreign body; yet this rectum so sensitive in\nits reaction on the stimulus of the pencil, responds by the totally\ndifferent reaction--the relaxation of the muscles--on the stimulus of\nf\u00e6cal matters.\n\n52. \u201cThis is all mechanical,\u201d you say? Mechanical, no doubt, as all\nactions are; but the question here is whether among the conditions of\nthe mechanical action Sensibility has a place? The answer can only be\ngrounded on induction. The actions of the dog are analogous to the\nactions which you know were sentient in yourself. There was in both a\ndiscrimination, in both a corresponding reaction. I admit that what is\nhere called \u201cdiscrimination\u201d is the application of a logical term to a\nmechanical process; I admit that if the spinal mechanism is insentient,\nthe fact of discrimination may still be manifested; but I conceive\nthat the many and coercive grounds for admitting that the mechanism is\nsentient gain further support in the evidence of discrimination. Every\nparticular sensation has its corresponding reaction; and although this\nhas been acquired during ancestral or individual experiences, so that\nin the majority of cases there is no consciousness accompanying the\noperation, this, as we have seen, is not a valid argument against the\nexistence of a sensorial process. We have only to lower the Sensibility\nof the cord by an\u00e6sthetics, or to _preoccupy_ its energies by some\nother excitation, and the reaction fails.\n\n\nMEMORY.\n\n53. \u201cBut discrimination, if not a purely physical process, implies\nMemory?\u201d No doubt. And what is Memory--on its physiological side--but\nan organized tendency to react on lines previously traversed? As\nGriesinger truly says: \u201cThere is Memory in all the functions of the\ncentral organs, including the spinal cord. There is one for reflex\nactions, no less than for sense-images, words, and ideas.\u201d Gratiolet\nmakes a similar assertion.[266] Indeed if, as we have seen, reflex\nactions are partly connate, and partly acquired, it is obvious that the\nsecond class must involve that very reproduction of experiences, which\nin the sphere of Intellect is called Memory.\n\nThere is assuredly something paradoxical at first in this application\nof the terms of the Logic of Signs, yet the psychologist will find\nit of great service. But if the terms discrimination and memory\nbe objected to, they may be replaced by some such phrase as the\n\u201cadaptation of the mechanism to varying impulses.\u201d On its objective\nside, Discrimination is Neural Grouping; on its subjective side, it is\nAssociation of experiences.\n\n\nINSTINCT.\n\n54. If we can detect evidences of Volition and Instinct in the\nabsence of the brain, our thesis may be considered less questionable.\nAnd such evidence there is. Goltz decapitated a male frog (in the\npairing season), and observed that it not only sought, grasped, and\nenergetically embraced a female, but could always discriminate a\nfemale from a male. Thus when a male frog closely resembling a female\nin size and shape was presented to this decapitated animal, he clasped\nit, but rapidly let it go again, whereas even the dead body of a\nfemale was held as in a vice. Goltz tried to _delude_ this brainless\nanimal in various ways, always in vain. Only a female would be held\nin his embrace. Goltz then presented a female in a reversed position,\nso that the head was grasped by the male. Now here, had there been\nsimply a reflex machine, incapable of sentient discrimination, the\nclutched female would have been held in this position, just like any\nother object which excited the reflex; there would have been no \u201csense\nof incongruity,\u201d such as Goltz noticed in his frog, who at once began\na series of movements by which he was enabled, without letting the\nfemale escape, to bring her into the proper position. To render this\nobservation still more significant, I may add that Goltz did not find\nall male frogs act thus--many relinquished the female thus improperly\npresented to them. Such phenomena observed in frogs possessing brains,\nwould be accepted as evidence of sexual instinct and volition.\n\nFurther: Goltz removed the brain from a frog, which he then held\nunder water, gently pressing the body so as to drive the air out of\nits lungs; the body being then heavier than the water sank to the\nbottom, where it remained motionless. He repeated this procedure with\nanother frog, not brainless but blinded. This one sank also, but in a\nfew minutes rose to the surface to breathe. This difference naturally\nsuggests that the brainless frog was insensible of the condition which\nin the other caused a movement of relief. The one felt impending\nsuffocation, the other felt nothing. Such was the interpretation of a\nGerman friend in whose presence I repeated the experiment. But I had\nbeen instructed by Goltz, and bade my friend wait awhile. He did so,\nand saw the brainless frog slowly rise to the surface and breathe there\nlike his blinded companion. So that the only difference observable was\nin the lessened sensibility of the brainless frog.\n\n55. But Goltz records a still more conclusive case. In a large vessel\nof water he inverted a glass jar also containing water, which could\nthen only be retained in the jar by atmospheric pressure. Through the\nneck of this inverted jar he thrust a blinded frog, not having pressed\nthe air out of its lungs. It rose at once in the jar, touching the\ninverted bottom with its nose, and when the necessity of fresh air\nwas felt, the frog began restlessly feeling about the surface of its\nprison till an issue was found in the neck of the jar, through which it\ndashed into the vessel, and at once rose to the surface of the water\nto breathe. In this observation are plainly manifested the stimulation\nof uneasy sensation, the volition of seeking relief, and the\ndiscrimination of it when found. If this frog was a sentient mechanism,\nwhat shall we say to the fact that a brainless frog was observed to\ngo through precisely the same series of actions? Goltz pertinently\nremarks: \u201cSo long as physiologists satisfied themselves that the\nbrain was the sole organ of sensation, it was easy to declare all the\nactions of the brainless animal to be merely reflex. But now we must\nask whether the greater part of these actions are not due to the _power\nof adaptation_ in the central organs, and are therefore to be struck\nout of the class of simple reflexes? If I bind one leg of a brainless\nfrog and observe that he not only sees an obstacle, but crawls aside\nfrom it, I must regard these movements as regulated by his central\npower of adaptation; but now suppose I unbind the leg and remove the\nobstacle, then if I prick the frog he hops forward. Must I now declare\nthis hop to have been a simple reflex? Not at all. In both cases the\nphysiological processes have been similar.\u201d\n\n       *       *       *       *       *\n\n56. There are no doubt readers who will dismiss all evidence drawn\nfrom experiments on frogs, as irrelevant to mammals and man. Let us\ntherefore see how the evidence stands with respect to animals higher\nin the scale, endowed with less questionable mental faculties. In a\nformer chapter (PROBLEM II. \u00a7 29) we recorded the marked results of\nremoving the cerebral hemispheres; and at the same time suggested that\nthese by no means justified the conclusion usually drawn respecting\nthe hemispheres as the exclusive seat of sensation. And this on two\ngrounds: First, because the absence of some sensitive phenomena does\nnot prevent the presence of others: the mutilated organism is still\ncapable of manifesting Sensibility in those organs which remain intact.\nSecondly, because were the mutilation followed by total destruction of\nSensibility, this would not prove Sensibility in the normal organism to\nhave its seat in the part injured. If the removal of a pin will destroy\nthe chronometric action of a watch, we do not thence infer that the\nchronometric action was the function of this pin. And this objection\nhas the greater force when we remember that one hemisphere may be\nremoved without the consequent loss of a single function, and both may\nbe removed without the loss of several functions usually ascribed to\ncerebral influence.[267]\n\n57. Consider the analogous effects of injuries to or removal of\nthe Cerebellum, in causing disturbance of locomotion, whence the\nconclusion has been drawn that the Cerebellum is the exclusive organ\nof muscular co-ordination, in spite of the unquestionable evidence\nthat very many muscular co-ordinations still persist after this organ\nis removed. What is the part played by the Cerebellum I do not pause\nhere to examine.[268] I only say that the movements of swimming,\nsucking, swallowing, breathing, crying, micturition, defecation,\netc., are co-ordinated as well after removal of the Cerebellum as\nthey were before, and that consequently _their_ co-ordination has not\nits seat in the Cerebellum. The parallelism is obvious. Removal of\nthe Cerebrum causes a disturbance in the combination of sensations,\nand the execution of certain sense-guided actions, but causes little\nappreciable disturbance in others. Removal of the Cerebellum causes\na disturbance in the combination of certain muscular sensations, and\nthe execution of certain co-ordinated actions, with little appreciable\ndisturbance in others.\n\n58. So little have the facts been surveyed and estimated in their\nentirety that there is perhaps no subject on which physiologists are\nmore agreed than on the function of the Cerebellum being that of\nco-ordination. Yet consider this decisive experiment. I etherized\nthree healthy frogs, from one I removed the entire cranial centres;\nfrom another I removed only the cerebellum; and, leaving the third\nin possession of an intact encephalon, I made two sections of the\nposterior columns of the spinal cord. The two first hopped, swam,\nused their legs in defence, and exhibited a variety of muscular\nco-ordinations, although in both the supposed organ of co-ordination\nwas absent. Whereas the third, which had this organ intact, and\nwas capable of moving each limb separately, and each pair of limbs\nseparately, was utterly incapable of moving all four simultaneously.\nWhy was this? Obviously because in the first two frogs the motor\nmechanism remained intact, and only the cerebral and cerebellar\ninfluence was removed; in the third frog the sensory part of the\nmotor mechanism had been divided, and no combination of the limbs was\npossible.\n\n59. Physiological induction agrees with anatomical induction in\nassigning to the cerebrum and cerebellum the office of _incitation_\nand _regulation_ rather than of _innervation_; for, as we have seen,\nno nerve issues directly from them (PROBLEM II. \u00a7 7). Consequently the\neffects of injuries to these centres are losses of spontaneity and of\ncomplexity in the manifestations. Inasmuch as in the intact organism\nall sensory impressions are propagated throughout the nervous centres,\nthe reactions of these highest centres will enter into the complex of\nevery adjusted movement; so the abolition of these centres will be the\ndropping of a link in the chain, the abolition of a special element\nin the complex group. The organs which are still intact will react,\neach in its own way, on being stimulated; but the reaction will be\nwithout the modifying influence of the absent centres. For instance,\nthe retinal stimulation from a luminous impression normally calls up a\ncluster of associated feelings derived originally from other senses,\nand a perception of the object is associated with emotions of desire,\nterror, etc., according to the past history of the organism, and its\norganized reactions, due to hereditary or acquired experiences. It\nis these which form the complex feeling discharged in the particular\nmovement of prehension, or flight. Remove the brain, and there can be\nno longer _this_ cluster of associated neural groups excited; there\nwill be therefore no emotion, simply the visual sensation, and such a\nmovement as is directly associated with it. The brainless dog moans\nwhen hurt, it does not bark at the cat which it nevertheless sees,\nand avoids as a mere obstacle in its path; the cat will cry, it will\nnot mew. The present pain moves the vocal organs, but does not revive\nassociated experiences. All those combinations by which a series of\ndependent actions result from a single stimulation are frustrated when\nthe mechanism is disturbed, so that the mutilated animal can no longer\nrecognize its prey or its enemy, to feed on the one and fly from the\nother; no longer builds its habitation, or rears its offspring. It\ncan still live, feed, sleep, move, and defend itself against present\ndiscomfort; it cannot find its food, or protect itself against\nprospective discomfort. We must supply the place of its Intelligence.\nWe must give it the food, and protect it from injuries.\n\nThere is therefore ample evidence to show that what is specially known\nas Intelligence is very imperfect after the cerebral influence has been\nabolished; but this does not prove the Cerebrum to be the exclusive\nseat of Intelligence, it only proves it to be an indispensable factor\nin a complex of factors. Still less does it prove the Cerebrum to be\nthe exclusive seat of Sensation, Instinct, Volition; for these may be\nmanifested after its removal, although of course even these will be\nimpaired by the loss of one factor.\n\n60. And here an objection must be anticipated. In spite of the\nfamiliar experience that one mode of Sensibility may be destroyed\nwithout involving the destruction of other modes, there is a\ngeneral belief--derived from a mistaken conception of what is really\nrepresented by the unity of Consciousness--that Consciousness\ndisappears altogether when it disappears at all; and hence, since\nSensation is supposed to imply Consciousness, it also cannot be\ndivisible, but must vanish altogether if it vanish at all. The first\nanswer is that Sensation as an abstraction is neither divisible nor\nindivisible; but as a generalized expression of concrete sensorial\nprocesses it is reducible to these processes, and divisible as\nthey are. No one doubts that we may lose a whole class of special\nsensations--sight, hearing, pain, temperature, etc.--yet retain all\nthe others. No one doubts that we may lose a whole class of registered\nexperiences--forget a language, or lose memory of places so familiar as\nthe streets of the small town we inhabit, or of faces so familiar as\nthose of friends and relatives, while the names of these streets and\nfriends are still remembered when the sounds are heard. Yet sensation\nand intelligence are not wholly lost. The mind is still erect amid\nthese ruins.[269]\n\n61. This premised, let us consider the experimental evidence. Flourens\ndeclares that when he removed the whole of the Cerebrum from pigeons\nand fowls, they lost _all_ sensation, _all_ perception, _all_ instinct,\nand _all_ volition. They lived perfectly well for months after the\noperation, if the food were placed in their mouths; but they never\n_sought_ their food; they never _took_ it, even when their beaks were\nplunged into it: they could swallow, and digest the grains; but they\nhad no instinct to make them seek, no volition to make them pick up\nthe grains. They _saw_ nothing, although the iris remained irritable;\nthey heard nothing; they could not smell. A state of stupor came on,\nresembling that of deep sleep. All voluntary action ceased. If they\nwere thrown into the air, they flew; if irritated, they moved away; but\nif left to themselves, they remained motionless, with the head under\nthe wing, as in sleep. Now, inasmuch as these effects always ensue\nwhen the Cerebrum is removed, and _never_ when only the Cerebellum is\nremoved, he concludes that all instincts, volitions, and sensations\n\u201cbelong exclusively to the cerebral lobes.\u201d\n\nBut all experimenters do not agree in other points named by Flourens;\nnor in the conclusions he has drawn. On the contrary, it is very\ncertain, and we find evidence even in Flourens himself, that all\ninstincts and all sensations are _not_ destroyed by the removal of the\ncerebral lobes.\n\n62. Let us hear Bouillaud on this subject.[270] He repeated the\nexperiment of Flourens, removing the whole of the Cerebrum from\nthe Brain of a fowl; and he thus records his observations: \u201cThis\nfowl passes the greater part of her time asleep, but she awakes at\nintervals, and _spontaneously_. When she goes to sleep, she turns her\nhead on one side and buries it in the feathers of the wing; when she\nawakes, she shakes herself, flaps her wings, and opens her eyes. In\nthis respect there is no difference observable between the mutilated\nand the perfect bird. She does not seem to be moved at all by the\nnoise made round about her, but a very slight irritation of the skin\nsuffices to awaken her instantaneously. When the irritation ceases,\nshe relapses into sleep. When awake, she is often seen to cast stupid\nglances here and there, _to change her place, and walk spontaneously_.\nIf put into a cage, _she tries to escape_; but she comes and goes\nwithout any purpose, or rational design. When either foot, wing,\nor head is pinched, she withdraws it; when she is laid hold of, she\n_struggles to escape, and screams_; but no sooner is she liberated than\nshe rests motionless. If severely irritated, she screams loudly; but\nit is not only to express pain that she uses her voice, for it is by\nno means rare to _hear her cackle and cluck a little spontaneously_;\nthat is to say, when no external irritation affects her. Her stupidity\nis profound; she knows neither objects nor places, nor persons, and is\ncompletely divested of memory in this respect: not only does she not\nknow how to seek or take food, she does not even know how to swallow it\nwhen placed in her beak--it must be pushed to the throat. Nevertheless\nher indocility, her movements, her agitation, attest that she _feels_\nthe presence of a strange body. Inasmuch as external objects excite in\nher no idea, no desire, she pays no attention to them; but she is not\nabsolutely deprived of the power of attention, for if much irritated\nher attention is awakened. She knows not how to escape an enemy, nor\nhow to defend herself. All her actions, in a word, are blind, without\nreflexion, without knowledge.\u201d\n\nIn this recital, the evidence both of _sensation_ and _instinct_ is\nincontestable, to any unprejudiced mind. Bouillaud, in commenting\non his observations, remarks, that assuredly _all_ sensation was\nnot destroyed, since the sensibilities of touch and pain were very\nmanifest. Nor is it certain, he says, that the fowl heard nothing, saw\nnothing. It is true that she stumbled against objects, and knew not how\nto avoid them. She opened her eyes on awaking, looked about, and showed\na sensibility in the pupil to light; which, he thinks, is incompatible\nwith the absence of all sensation of sight\n\n63. The experiments of Longet[271] seem decisive on this latter point.\nHaving removed the whole of the Cerebrum from a pigeon, he observed\nthat whenever he approached a light brusquely to its eyes, there was\ncontraction of the pupil, and even winking; but, what was still more\nremarkable, \u201cwhen I gave a rotatory motion to the candle, and at such\na distance that there could be no sensation of heat, the pigeon made\na similar movement with its head. These observations, renewed several\ntimes in the presence of persons who were at my lectures, left no\ndoubt of the persistence of sensibility to light after removal of the\ncerebral lobes.\u201d We have only to think of the baby following with its\neyes the light moved before it, to understand the kind of impression\nproduced by the candle on the pigeon. Longet also declares that his\nexperiments prove the existence of sensations of sound, after removal\nof the whole cerebrum.\n\n64. Dr. Dalton, giving the results of numerous experiments he\nperformed, says that removal of the Cerebrum plunges the animal in\n\u201ca profound stupor, in which he is _almost_ entirely inattentive to\nsurrounding objects.... Occasionally the bird opens its eyes with a\nvacant stare, stretches his neck, perhaps shakes his bill once or\ntwice, or smoothes down the feathers upon his shoulders, and then\nrelapses into his former apathetic condition. This state of immobility,\nhowever, is _not_ accompanied by the loss of sight, of hearing, or of\nordinary sensibility. _All these functions remain, as well as that\nof voluntary motion._ If a pistol be discharged behind the back of\nthe animal, he at once opens his eyes, moves his head half round, and\ngives evident signs of having heard the report; but he immediately\nbecomes quiet again, and pays no further attention to it. Sight is also\nretained, since the bird will sometimes fix its eye on a particular\nobject, and watch it for several seconds together.\u201d[272]\n\nWhile, therefore, Flourens concludes from his experiments that the\nCerebrum is the seat of _all_ sensation and all volition; and Bouillaud\nconcludes that it is most probably the seat of _none_; Dr. Dalton\nconcludes that the functions of the Cerebrum are restricted to those\nusually classed as intellectual. \u201cThe animal,\u201d he says, \u201cis still\ncapable, after removal of the hemispheres, of receiving sensations\nfrom external objects. But these sensations appear to make upon\nhim no lasting impression. He is incapable of connecting with his\nperceptions any distinct succession of ideas. He hears, for example,\nthe report of a pistol, but he is not alarmed by it; for the sound,\nalthough distinctly perceived, does not suggest any idea of danger or\ninjury. The memory is altogether destroyed, and the recollection of\nsensations is not retained from one moment to another. The limbs and\nmuscles are still under the control of the will; but the will itself\nis inactive, because apparently it lacks its usual mental stimulus and\ndirection.\u201d[273]\n\nDr. Dalton reminds us how disturbance of the cerebral functions in\nhuman beings recalls these observations on animals. \u201cIn cases of\nimpending apoplexy, or of softening of the cerebral substance, among\nthe earliest and most common phenomena is a loss or impairment of\nthe memory. The patient forgets the names of particular objects, or\nparticular persons; or he is unable to calculate numbers with his usual\nfacility. His mental derangement is often shown in the undue estimate\nwhich he forms of passing events. He is no longer able to appreciate\nthe true relation between different objects and different phenomena.\nThus he will show an exaggerated degree of solicitude about a trivial\noccurrence, and will pay no attention to other matters of importance.\nAs the difficulty increases, he becomes careless of the directions and\nadvice of his attendants, and must be watched and managed like a child\nor an imbecile. After a certain period he no longer appreciates the\nlapse of time, and even loses the distinction between day and night.\nFinally, when the injury to the hemispheres is complete, the senses may\nstill remain active and impressible, while the patient is completely\ndeprived of intelligence and judgment.\u201d[274]\n\n65. Having seen how far other experimenters are from confirming the\nconclusions of Flourens, let us glance at his record of observations,\nand we shall find there evidence that _all_ sensation and _all_\nvolition cannot be localized in the Cerebrum. Speaking of a fowl whose\nCerebrum was removed the day before, he says: \u201cShe shakes her head\nand feathers, sometimes even she cleans and sharpens them with her\nbeak; sometimes she changes the leg on which she sleeps, for, like\nother birds, she sleeps habitually resting upon one leg. In all these\ncases she seems like a man asleep, who, without quite waking, changes\nhis place, and reposes in another, from the _fatigue_ occasioned by\nthe previous posture: he selects one more _comfortable_, stretches\nhimself, yawns, shakes himself a little, and falls asleep again.... On\nthe third day the fowl is no longer so calm; she comes and goes, but\nwithout motive and without an aim; and if she encounters an obstacle\non her path, she knows not how to avoid it.\u201d[275] In his second work\nhe remarks of a Duck operated on in the same way: \u201cAs I mentioned last\nyear _\u00e0 propos_ of fowls, the duck walks about oftener, and for a\nlonger time together, when it is fasting, than when it is fed.\u201d\n\nHere he observes the unmistakable evidence of feelings of Hunger,\nFatigue, and Discomfort in animals which, according to him, have lost\n_all_ sensation. He also observes the operation of instinct (cleaning\nthe feathers), and of spontaneous activity (walking about), in animals\nsaid to have lost _all_ instinct and _all_ volition.\n\n66. Still more decisive are the observations recorded by other\nexperimenters. Leyden removed the hemispheres _and_ the ganglia at\ntheir base from a hen; yet this hen moved about and clucked. Meissner\nnoticed that a pigeon whose hemispheres had been removed always uttered\nits _coo_, and showed restlessness at the usual feeding-time.[276]\nVoit carefully extirpated the cerebrum from some pigeons, and kept\nthem for many months in health. For the first few weeks they exhibited\nthe well-known stupor. Then they began to shake this off, open their\neyes, walk, and fly about _spontaneously_. They gave unmistakable\nsigns of seeing and hearing. But the chief defect was in the inability\nto feed themselves, and the complete insensibility to danger. They\nalso manifested signs of sexual feeling with lively cooings; though\nquite unable to gratify their desires.[277] Vulpian having removed\nthe cerebrum, optic thalami, and corpora striata from a young rabbit,\nfound that on pinching its tail it cried out and struggled to\nescape; and a rat thus mutilated not only struggled and cried when\npinched, but manifested strong emotion. \u201cIl est tr\u00e8s craintif, tr\u00e8s\nimpressionable; il bondit pour peu qu\u2019on le touche; le moindre bruit le\nfait tressaillir. Un certain bruit d\u2019appel fait avec les l\u00e8vres, ou un\nsoufflet brusque imitant celui qu\u2019emettent les chats en col\u00e8re excitent\nchez le rat une vive \u00e9motion.\u201d[278]\n\n67. There are several well-authenticated cases on record of children\nborn without a vestige of brain, and others with only a vestige, who\nnevertheless manifested the ordinary signs of sensation. I will cite\nbut one, and it shall be one for which an illustrious physiologist,\nPanizza, is the guarantee. A male infant, one of twins, who lived but\neighteen hours, during that period manifested such unquestionable signs\nof Sensibility as the following: the pupils contracted under light,\nsharp sounds caused flutterings, and a bitter solution when placed in\nthe mouth was instantly rejected. This infant had not a vestige of\ncerebrum, cerebellum, or cerebral ganglia. The medulla oblongata was\nnormal. There were no olfactory nerves, and the optic nerves terminated\nin a little mass of membrane.[279]\n\n68. The observations of Lussana and Lemoigne are both extensive and\nprecise, and the conclusion at which they arrive is that the removal\nof the Cerebrum is the abolition of Intelligence and Instinct, but is\nnot the abolition of Sensation. Whereas Rolando, and after him Renzi,\nconsider that only the Intelligence is abolished, the supposed loss\nof Instinct being really nothing more than the loss of the directive\ninfluence which makes the Instinct to be executed.\n\n69. Here it becomes needful to understand\n\n\nTHE MECHANISM OF INSTINCT.\n\nWere we dealing with an ordinary mechanism, and the disturbances\nproduced in its actions by the removal of any part, we should attribute\nall observed effects to _interference with the conditions of dependent\nsequence_: we should infer that the actions were imperfectly performed,\nor wholly abolished, because their requisite mechanical conditions were\ndisturbed. Let us be equally precise in dealing with the physiological\nmechanism. If we have deprived it of an organ in which certain\ncombinations are effected, we must expect to find all actions which\nwere dependent on such combinations to be now impossible; but all the\nactions which are not directly dependent on these combinations may\nstill be possible. The actions of feeding, for example, are determined\nby certain sensations, when these are present in a particular sequence,\nbut not otherwise; the sensation of sight does not suffice, because\nthe animal must not only _see_ the food, he must _perceive_ it. The\naction of defence and flight are also determined by certain sensations,\nbut only when these are connected in a certain sequence: the brainless\nanimal will defend itself, or move out of the way, under the stimulus\nof unpleasant sensation; but will not be moved by a _prospective_\ninjury, because he fails to associate it with the sight of the\nthreatening object. In the same way a blind man shrinks at the actual\ncontact of the heated poker, but does not shrink at the approach of\nthat poker which he does not see. We do not deny him the possession\nof the so-called instinct of Self-preservation on this ground; why\ndeny it to the brainless animal? The brainless fish or frog swims when\nplaced in the water, because the sensation from the _moving_ water[280]\nsets going the swimming mechanism. To call this a \u201cswimming instinct\u201d\nmay seem extravagant; yet it is as fully entitled to the name as\nSelf-defence is, or the Alimentary Instinct. In all three cases there\nis a connate mechanism set going by appropriate feelings.\n\n70. Since all admit that there is an Alimentary Instinct, let us see\nwhat kind of mechanism it implies. There must be a state of feeling\ncalled Hunger, which--combined with other feelings--determines certain\nmuscular adjustments in the search, recognition, capture, and finally\nthe swallowing of the food:--a very complex series of actions, which\nlead to and sustain one another until the desire is gratified. On the\nmental side there are three constituents, all indispensable: the\nhunger must be felt, the food must be discriminated, the desire must\nbe gratified; on the physical side there are also the indispensable\narrangements of the motor mechanism. Now it is obvious that the\n_entire_ mechanism of this instinct cannot be localized in the brain,\neven if its mental elements are localized there; and there is reason\nto believe that even the mental elements--the feelings of hunger,\ndiscrimination, and gratification--are not exclusively localized there.\nThe brainless animal manifests if not the feeling of Hunger, at any\nrate that feeling of discomfort which is the basis of Hunger. The\nrestlessness is that of a hungry animal. Now we know that some of the\nSystemic Sensibility is preserved, for we see the animal breathing,\nswallowing, urinating, sleeping, preening its feathers, changing its\nattitude, resting on one leg after the fatigue of the other, etc. We\nmay therefore infer that other systemic sensations, such as Hunger and\nThirst, arise under the usual conditions.\n\n71. We have noted an indication of Hunger; but on further observation\nwe discover that although the food is eaten, if brought within reach\nof that portion of the feeding mechanism which is still intact, yet\nthe second step--the feeling of recognition--is wanting. The animal\nfails to perceive the food brought under his eyes, or even placed in\nhis mouth; unless the back part of the mouth be touched, no swallowing\ntakes place. Hence the animal can no longer feed himself, and is\ntherefore said to have lost his instinct. But although the mechanism\nof the instinct has been _disturbed_, its action is not wholly\nabolished. The brain is necessary for that combination of adjustments\nwhich normally accompany the perception of food through sight and\nscent; and its absence of course frustrates such combination; but we\nshall presently see that although certain sensible marks by which a\nperception is guided are absent, others may still be present, and\nsuffice.\n\n72. Before adducing examples let me say that we cannot legitimately\nattribute the abeyance of an instinct solely to the absence of the\nbrain, 1\u00b0, because we observe a similar abeyance of the instinct and\nfrustration of perception, even when the brain is present, and the\nanimal is in its normal state. 2\u00b0. On the other hand, some instincts\nare unmistakably manifested, and some perceptions excited, after the\nbrain has been removed. In fact, all that is needful is that some of\nthe mental elements of such perception and such instinct be preserved;\nand this is the case so long as the leading element is present.\n\n73. On the first point consider this unequivocal example. A healthy,\nhungry frog may be placed in a vessel in which lie a quantity of dead\nflies. He sees these flies, but sight is not enough; to him they are\nonly so many black spots, in which he does not recognize his food,\nbecause the flies do not move, and the _leading element_ in his\nperception of food is not a _colored_ form, but a _moving_ form. Hence\nthis frog, in spite of brain and an intact organism, will starve amidst\nappropriate food. Whereas the frog that will not snap at motionless\nflies snaps at any other small moving object, though it be not his\nfood. Goltz observed one incessantly snapping at the moving tentacles\nof a slug which was in the vessel--as if that were possible food! Not\nonly the stupid frog, but the more intelligent carnivora will starve\nin the presence of appropriate food which is unrecognized, because the\nleading element in the recognition is absent. The cat will not eat a\ndead mouse, unless she has killed it herself. Predatory animals must\ncapture their food--unless the scent of blood excites their alimentary\ninstinct. So intimately is this sensation of a moving object connected\nwith the predatory impulse, that the cat which is unexcited by the dead\nmouse cannot resist springing on a moving ball. We need not suppose the\ncat to mistake this ball for food; but we must suppose that, accustomed\nto pounce upon moving food, it is unable to resist the impulse of this\nleading sensation.\n\n74. The _presence_ of the brain not sufficing, in the absence of the\nleading sensation, we shall now see that the _absence_ of the brain\nwill not prevent the execution of the instinctive action, if the\nleading sensation be present. The brainless bird sees a heap of grain,\nor a pan of water, but no more recognizes them by sight alone than the\nfrog recognizes the dead flies; yet if the bird\u2019s feet be placed in\nthe water, _this_ sensation will suffice to make him drink; if placed\namid the grain, this sensation will (sometimes) suffice to make him\nfeed. Lussana and Lemoigne state that their brainless pigeons ate and\ndrank with avidity when their feet were placed in grain and water.[281]\nM. Krishaber removed the hemispheres from a pigeon, and observed that\nwhen his beak was thrust into a heap of hempseed the head was quickly\nwithdrawn, whereas when the beak was plunged into water the bird drank\neagerly. Every day he was forced to feed the bird by pouring the seed\ninto its throat, but every day it drank when the beak was thrust into\nthe pan of water.[282] Br\u00fccke noticed that his brainless hen, which\nmade no attempt to peck at the grain under her very eyes, began pecking\nif the grain were thrown on the ground with force, so as to produce a\nrattling sound. The sensation of hearing was here more perfect than\nthat of vision, and sufficed to awaken the state of feeling necessary\nto initiate the pecking movement.[283]\n\n75. Somewhat analogous phenomena are observed in Aphasia. The patient\ncan see printed or written letters, and even copy them; but he cannot\nread, i.\u00a0e. interpret, these symbols; as the birds see the grain, but\ncannot connect this sensation with others. These letters and words,\nwhich the patient cannot interpret when _seen_, he can interpret when\n_heard_; he can not only understand them when spoken, but write them\nif they are dictated to him. The birds recognize the grain and water\n(or act as if they did) when other sensations than those of sight\nare excited. Sound is the leading element in Language, both spoken\nand written. We hear the words even when we see them, but we do not\nsee them when we hear them. The visible symbols are accessory and\nsubordinate. But to the born deaf the visible symbols dominate. How one\nsensation will determine a particular group of movements which cannot\nbe effected by any other stimulus is abundantly illustrated in disease\nno less than in experiment. Here is a very luminous example: Gratiolet\nhad a patient for six months under his eye incapable of articulating a\nsingle word, owing to the incoherence of her incessant utterance--she\nbabbled sounds, but could not group the syllables into a recognizable\nword. Yet she could sing the words of any song she knew, the musical\nsensations being sufficient to guide her vocal organs. \u201cAinsi la\nm\u00e9moire, infid\u00e8le dans le cas o\u00f9 les mots \u00e9taient des id\u00e9es, devenait\nclaire et pr\u00e9cise quand les mots \u00e9taient des chansons.\u201d[284]\n\n76. These illustrations plainly tell how the brainless animal may\nstarve amid his food, failing to perceive it because the leading\nsensation is not excited; and how the same animal may manifest his\nfeeding instinct if the mechanism be set going by a leading sensation.\nWe are told, indeed, that in the absence of the brain the actions are\nmechanical reflexes from impressions, and not comparable with the\ncomplex processes determined by perception. I think, however, that the\nonly difference is in degree of complexity: a combination of touch,\ntemperature, and muscular movement will be simpler than one which also\ncombines sight, smell, and the revived images of associated sensations.\nThe sight of a sheep affects the instinctive mechanism of a wolf _only_\nwhen combined with the leading element of smell. Place a stuffed sheep\nin a field, and no wolf will approach and spring on it, whereas the\nblind wolf will find and capture the real sheep; and I believe that\nwere it practicable to remove the brain without injury to the organ of\nscent and the powers of locomotion, the wolf would track and capture\nthe living sheep.\n\n77. The outcome of this discussion is that the mechanism of each\ninstinct is the adjustment of the organs which effect the instinctive\naction; and this adjustment is not simply a cerebral process, but\na complex of _many_ sensorial processes; consequently the instinct\ncannot be exclusively localized in the brain, although the cerebral\nprocess may be a very important element in the adjustment. This is\ntrue even on the supposition that in speaking of Instinct we refer\nonly to the state of feeling which originates the action--separating\nthe psychological from the physiological aspect of the phenomenon. For\nthe brain _minus_ the organism is obviously incapable of feelings;\nwhereas the organism _minus_ the brain is obviously capable of\nsensibilities adequate to determine the actions. Thus the feeling\nof hunger which prompts the alimentary actions does not arise if\nthe animal is satiated, nor does the sexual feeling which prompts\ngenerative actions arise when the animal is castrated; but each arises\nwhen the organism is in a particular state. In vain will food be placed\nbefore the satiated animal, or a female before the castrated male;\nfood and female are seen and recognized, but no desires are excited,\nin spite of the brain and its supposed instincts. On the contrary,\nwhen the brain is removed, the need of the organism for food is felt,\nand this need determines restless movements, which are directed by\ncertain other sensations, and the instinctive action of feeding is\nfinally effected; although, of course, the removal of the brain has\nso disturbed the normal mechanism of the instinct that the action is\nimperfect. Renzi says that an animal deprived of its brain has lost\nthe intelligence which enables it to seek and seize its food, but not\nthe instinct, since it still has the desire for food. The following\nexperiment may illustrate this. Renzi wounded superficially one optic\nthalamus of a frog without injuring the external margin, or optic\ntract. The frog showed no appreciable loss of sight, but hopped timidly\naway whenever approached. Then both thalami were divided transversely,\nthe optic tract still being spared. This frog remained motionless\nunder every threat. It manifested no alarm, and even when directly\nirritated, only crawled or hopped away like a brainless frog. Sight\nstill so far remained that obstacles were avoided.[285] Now since this\nanimal\u2019s brain was intact, and its organs of movement were capable\nof responding to stimulation, how are we to explain the loss of its\ninstinct of self-preservation? The frog perceived no danger in a\nthreatening approach, yet perceived an obstacle and avoided it, getting\nunder it if there were room enough, crawling beside it if that was\nthe easier escape. Why did one vision prompt the movements of escape,\nand another fail? Was it not that in the one case the normal pathway\nwas still open, in the other closed? We know that one injury will\ndestroy the perception of color without destroying that of light and\nshadow; so one injury may destroy the combination of neural processes\nnecessary for the perception of a _danger_, without destroying those\nnecessary for the perception of a _hindrance_. If all actions depend\non their mechanical conditions, they must be disturbed according to\nthe disturbance of the conditions. Nothnagel found that after removing\nthe _nucleus lentiformis_ on both sides of a rabbit, leaving all the\nrest of the encephalon intact, the rabbit hopped when its tail was\npinched; yet although starting at the sound when hands were loudly\nclapped, did not hop as a normal rabbit does; nor although closing his\neyes when a light was brought near them, did he ever move aside. No\nfeeling of danger was excited by sound or sight. In striking contrast\nare the phenomena manifested by a rabbit whose _corpora striata_ have\nbeen removed: it is with difficulty made to hop by pinching its skin,\nwhereas noises and sights cause it to make terrified bounds.[286]\n\n78. No sooner do we analyze the conditions of an instinct than we\nsee the error of regarding instincts as localized in the brain. The\ncerebral process is only one factor in the product--an important\nfactor, no doubt, since the cerebrum is the supreme centre of\nincitation and regulation; but its absence does not wholly carry\naway the activity of the mechanism, sentient and motor, on which the\ninstincts depend, it only carries away one source of stimulation and\nregulation.\n\n79. An instinct depends on a connate mechanism. Let us glance for a\nmoment at a parallel case of an ordinary reflex action, also dependent\non a connate mechanism, say that of sneezing. When the inner surface\nof the nose is stimulated by snuff, or other irritant, the nasal\nbranch of the trigeminus is excited, and the effects are first a deep\ninspiration, then a closure of the respiratory orifices by the tongue,\nwhich in turn excites a spasmodic expiration. But the same effects\nare producible from quite different stimulations--namely, that of the\nciliary nerves on sudden exposure to a glare of sunshine--or of the\nskin nerves on a sudden draught of cold air. Br\u00fccke remarks that there\nis perhaps no spot on the surface of the body from which this reflex\nmay not be excited in very sensitive people. He knew a gentleman who\nalways sneezed when in winter he laid hold of a cold door-bell; and the\nfit of sneezing was only arrested by giving him a crust of bread or\nsomething hard to gnaw. Now just as the connate mechanism of sneezing\nmay be set in action by a variety of stimulations, so may the connate\nmechanism of an instinct.\n\n\nACQUISITION.\n\n80. Not only may Discrimination and Instinct be manifested in the\nabsence of the brain, but even the acquisition of new modes of\nreaction, such as are classed under Learning through Experience.\nThe objection is sometimes urged that animals without their brains\nonly manifest single reactions on stimulation--the pinched foot\nis withdrawn, and then remains motionless until again pinched.\nBut although the stimulation does not excite a consecutive series\nof movements, because there is no cerebrum to react in successive\nstimulation, this does not prove the absence of sensation in the one\nmovement which is excited. If my hand be lying on the table, and\nsomething irritates it, my hand is withdrawn, and then remains as\nmotionless as the limb of the brainless animal, _until_ some fresh\nstimulation, external or internal, moves it. Although removal of\nthe brain causes a manifest reduction in the variety and succession\nof the movements, all experimenters are agreed that animals acquire\na certain dexterity in executing actions which they had previously\nfailed to carry out after removal of their brains. \u201cThere is,\u201d says\nFreusberg, \u201ca decided improvement acquired in the reactions of the\nmotor centres after division of the spinal cord, not indeed in vigor,\nbut in delicacy. Removed from the regulating influence of the brain,\nthe legs acquired through practice a power of self-regulation.\u201d Nor\nis this wonderful: pathways are made easy by repetition of impulses,\nand new adaptations form new adjustments. It is thus all learning is\neffected--intelligent, and automatic. Nor is there any force in the\nobjection that the power thus acquired speedily disappears, so that if\nthe stimulations are effected at long intervals the reactions do not\nmanifest their acquired dexterity. The spinal centres forget, as the\ncerebral centres forget; but they also remember, i.\u00a0e. they learn.\nBecause an animal shows to-day none of the aptitude it acquired three\ndays ago, we are not to deny that it had once acquired the aptitude it\nhas now lost. Attempt to teach a child to read by giving it spelling\nlessons of two or three minutes at intervals of two or three months,\nand little will the acquisition be!\n\n       *       *       *       *       *\n\n81. Hitherto we have been considering phenomena manifested in the\nabsence of the cerebral hemispheres, because it is in these that the\nmajority of writers place the sensorium. There are, indeed, many\nauthoritative writers who regard the ganglionic masses at the base of\nthe cerebrum, and even those of the medulla oblongata, as participating\nin this sensorial property, which they refuse to the lower ganglia in\nthe spinal cord. I cannot follow their logic. The cerebrum is by its\nposition as a centre of centres, and its detachment from all direct\ninnervation of organs, so different from the rest of the neural axis,\nthat we can understand how it should be assigned a special function;\nalthough being of the same tissue as the other ganglionic masses, it\nmust have the same property. And what that special function is I shall\nhereafter endeavor to set forth. But that the upper region of the\nspinal axis should differ so profoundly from the lower region as to\nbe the seat of psychical processes, while the lower region is simply\nthe seat of mechanical processes, is what I cannot understand, so\nlong as the anatomical structure and physiological properties of the\ntwo regions are seen to be identical. The various centres innervate\nvarious organs, and have consequently various functions. As each centre\nis removed, we observe a corresponding loss of function--the organism\nis truncated, but continues to manifest such functions as have still\ntheir mechanisms intact. Let us suppose the brain or upper regions of\nthe cord detached from the lower regions by a section of the cord; the\nanimal will still live, and perform almost all its functions in the\nnormal way, but there will be little or no consensus between the lower\nand the upper regions. Granting Sensibility to both, we must still see\nthat the sensation excited in one will not be felt in the other. And\nthis is the ground on which physiologists deny that the lower regions\nhave Sensibility. Without pausing here to examine this point, which\nwill occupy us in the next chapter, I assume that the positive evidence\nof Sensibility suffices to discredit that argument; and in furtherance\nof that assumption will cite an example of sensation and volition\nmanifested by the lower portion of the cord when separated from the\nbrain and upper portion.\n\n82. The function of Urination is one which notoriously belongs to\nthe voluntary class, in so far as it is initiated or arrested by a\nvoluntary impulse, and it is one which, according to the classic\nteaching, has its centre in the brain. The grounds on which this\ncerebral centre is assigned are very similar to those on which other\nfunctions are assigned to cerebral centres, namely, observation of the\nsuppression of the function when the pathway between certain organs and\nthe brain is interrupted. But the careful experiments of Goltz[287]\nhave demonstrated that the \u201ccentre\u201d of Urination is not in the brain,\nbut in the lower region of the cord. When the cord is completely\ndivided, Urination is performed in the _normal_ way--not passively,\nnot irregularly, but with all the characters of the active regular\nfunction. And, what is also noticeable, this function is so intimately\ndependent on Sensibility that it will be arrested--like any other\nfunction--by a sensation excited from the periphery--to be resumed when\nthe irritation ceases. Now this arrest from a stimulation of sensory\nnerves takes place when the brain is cut off from the spinal centre,\njust as when the brain is in connection with it.\n\nThe same is true of Defecation, and the still more complex functions\nof Generation and Parturition. I can only refer the reader to the\nvery remarkable case of Goltz\u2019s bitch with the spinal cord divided\nin the lumbar region, if evidence be wanted for the performance of\ncomplex functions so long as the spinal centres were intact. It is\ntrue that Goltz considers these functions to have been independent\nof _sensation_; but that is because he has not entirely emancipated\nhimself from the traditional views; for my purpose it is enough that he\nadmits the functions to be dependent on sensorial processes.\n\n       *       *       *       *       *\n\n83. To sum up the evidence, we may say that observation discloses a\nsurprising resemblance in the manifestations of the cord and brain. In\nboth there are reflex processes, and processes of arrest; in both there\nare actions referable to conscious and unconscious processes; in both\ndepression and exaltation are produced by the same drugs; in both there\nare manifestations interpretable, as those of Discrimination, Logic,\nInstinct, Volition, Acquisition, Memory; in both there is manifestation\nof Sensibility--how then can we deny Sensation to the one if we accord\nit to the other?\n\n\n\n\nCHAPTER IV.\n\nNEGATIVE INDUCTIONS.\n\n\n84. I fancy some reader exclaiming: \u201cAll your reasoning, and all your\nmarshalled facts, are swept away by the irresistible evidence of human\npatients with injured spinal cords, whose legs have manifested reflex\nactions, and who nevertheless declared they had _no sensation whatever_\nin them. We can never be sure of what passes in an animal; but man can\ntell us whether he feels an impression, or does not feel it; and since\nhe tells us that he does not feel it, _cannot_, however he may _try_,\nwe conclude that reflex action may take place without sensation.\u201d\n\nAs this is the one solitary fact which is held to negative the mass of\nevidence, anatomical and physiological, in favor of the Sensibility of\nthe spinal cord, it is necessary that we should candidly examine it.\nNo reader will suppose that during the twenty years in which I have\nadvocated the doctrine expounded in this volume, I have not been fully\nalive to the one fact which prevented the general acceptance of the\ndoctrine. From the first it has seemed to me that the fact has been\nmisinterpreted.\n\n85. Certain injuries to the spinal cord destroy the connection of\nthe parts below the injury with the parts above it; consequently no\nimpression made on the limbs below the injured spot is transmitted\nto the brain, nor can any cerebral incitation reach those limbs. The\npatient has lost all consciousness of these limbs, and all control\nover them. Hunter\u2019s patient on being asked if he felt any pain when the\nprick caused his leg to kick, answered, \u201cNo: but you see my leg does.\u201d\nThis answer has been regarded as a drollery; I think it expressed\na physiological truth. For on the assumption that the whole of the\ncerebro-spinal axis had one uniform _property_, corresponding with\nits uniform structure, and various _functions_, corresponding with\nthe variety of organs it innervates, a division of this axis would\nnecessarily create two independent seats of Sensibility, and interrupt\nthe consensus of their functions. In such a case it would be absurd to\nexpect that the cerebral segment could be affected by, or co-operate\nwith, what affected the spinal segment.\n\nNow, when a man has a diseased spinal cord, the seat of injury causes,\nfor the time at least, a division of the whole group of centres into\ntwo independent groups. For all purposes of sensation and volition it\nis the same as if he were cut in half; his nervous mechanism _is_ cut\nin half. How then can any cerebral control be obeyed by his legs; how\ncan any impression on his legs be felt by his cerebrum? As well might\nwe expect the man whose arm has been amputated, to feel the incisions\nof the scalpel, when that limb is conveyed to the dissecting-table, as\nto feel by his brain impressions made upon parts wholly divorced from\norganic connection with the brain.\n\n86. But, it may be objected, this is the very point urged. The man\nhimself does not feel the impressions on his legs when his spine has\nbeen injured; he is as insensible to them as to the dissection of his\namputated arm. Very true. _He_ does not feel it. But if the amputated\narm were to strike the anatomist who began its dissection, if its\nfingers were to grasp the scalpel, and push it away, or with the thumb\nto rub off the acid irritating one of the fingers, I do not see how\nwe could refuse to admit that the _arm_ felt although the _man_ did\nnot. And this is the case with the extremities of a man whose spine is\ninjured. _They_ manifest every indication of sensibility. In the frog\nand pigeon the legs manifest the unmistakable control which we ascribe\nto volition. It is true that the man himself, when interrogated,\ndeclares that he feels nothing; the cerebral segment has attached to\nit organs of speech and expressive features, by which _its_ sensations\ncan be communicated to others; whereas the spinal segment has _no_ such\nmeans of communicating _its_ sensations; but those which it _has_, it\n_employs_. You can ask the cerebral segment a question, which can be\nheard, understood, and answered; this is not the case with the spinal\nsegment: yet if you _test_ its sensibility, the result is unequivocal.\nYou cannot ask an animal whether it feels, but you can test its\nsensibility, and that test suffices.\n\n87. The question we have to decide, therefore, is not whether a\npatient, with an injured spine, can feel impressions on, or convey\nvoluntary impulses to, limbs below the seat of injury--for as respects\nthe nervous mechanism these limbs are separated from him, no less\nthan if actual amputation had taken place--the question is, whether\nthese separated limbs have any sensibility? And the answer seems to\nme unequivocally affirmative. I assert, therefore, that if there is\nample evidence to show that the spinal centres have sensibility, when\nseparated from the cerebral centres, such evidence can in no respect be\nweakened by the fact that a man with an injured spine is unconscious\nof impressions made below the seat of injury; since such a fact\nnecessarily follows from the establishment of two centres: the parts\nabove are then not sensitive to impressions on the parts below; nor are\nthe parts below sensitive to impressions on the parts above; but each\nsegment is sensitive to its own affections.\n\n88. Every one knows that there are animals, low down in the scale,\nwhich may be cut in two, each half continuing to live, and each capable\nof reproducing its lost segments. Would any one, seeing these separated\nhalves move and manifest ordinary signs of sensibility, venture to say\nthat the one half was a living, the other an insentient, mechanism?\nAnd since the one half had eyes, mouth, tentacles, etc., while the\nother half had none of these, would the observer be surprised that\nthe functions of the one differed from those of the other in these\nrespects? Why, then, should he not conclude the same of the two halves\nof the human mechanism, when disease had divided them?\n\n89. The man, you urge, does not feel the prick on his leg. This is\ntrue, because \u201cthe man\u201d here designates the seeing, hearing, tasting,\nsmelling, talking, thinking group of organs--to the exclusion of the\nlimb or limbs which are no longer in sensitive connection with this\ngroup. When a leg is amputated \u201cthe man\u201d remains--a truncated man,\nindeed, yet still one having all the distinguishing human characters.\nYet obviously in strict language we can no longer say that the man is\nthe _same_ as he was. \u201cMan\u201d or \u201canimal\u201d means the complex whole; and\neach anatomically separable part forms one constituent of that whole.\nThe medulla oblongata and spinal cord innervate certain parts; the\nmesencephalon innervates others; the cerebrum rises above the whole.\nIf after removing one limb, then another, we continued truncating the\norganism till we left only the head, should we call _that_ the man?\nClearly not. Should we even suppose that the intact brain--the supposed\nseat of sensation and volition--still felt, and willed? Clearly not.\nThere is absolutely no evidence, however faint, of the isolated head\nmanifesting any sensational and volitional phenomena; whereas there\nis ample evidence of the truncated spinal cord manifesting some of\nthese phenomena. And this is intelligible when we understand that the\nnerve-centres stimulate into action the organs they innervate, but do\nnot by themselves play any other part.\n\n90. \u201cThe man\u201d then does not feel the prick on his leg, but his leg\nfeels it. The man has no consciousness of what takes place outside the\nsphere of his sensitive mechanism; and the leg is now outside that\nsphere. Consciousness--as distinguished from Sentience in general--we\nhave seen to be a resultant of the composition of forces co-operating\nat the moment; the Sensibility of the spinal cord in the regions below\nthe injury cannot _now_ enter into that composition. It is detached\nfrom the upper organs. But inasmuch as the organs it innervates are\nstill living and active, the functions of this detached portion are\nstill displayed. We have seen the dog with divided cord capable of\nUrination, Defecation, Generation, etc.; its hinder legs, though not\nmoving in a consensus with the forelegs, yet moved independently; and\nall the normal reflexes of the parts followed on stimulations. To say\nthat \u201cthe dog\u201d showed no signs of Sensibility when its hinder limbs\nwere irritated, is identifying \u201cthe dog\u201d with the anterior half of the\norganism which was not in connection with the posterior half. It is\nequally true that the posterior half showed no signs of Sensibility\nwhen the anterior was irritated. The two halves were united by the\ncirculation, nutrition, etc., but disunited as to sensation and\nvolition.\n\n91. Do I then suppose the separated half of an animal to feel pain and\npleasure, hope and terror? The reader who has attentively followed\nthe exposition will be at no loss to answer. Pain, pleasure, hope,\nand terror, are special modes of Sensibility, dependent on particular\nneural combinations. The organs comprised in the anterior half of the\nanimal furnish the main conditions for these special modes, whereas\nthe organs comprised in the posterior half furnish few or none of\nthose--they contain none of the special Senses, and they are without\nthe chief combining centre, the brain. But since we know that a large\namount of normal Sensation is wholly without the special characters\nof pain, pleasure, hope, or terror, we need not hesitate to assign\nSensation to the spinal cord because these characters are absent.\n\n92. All I contend for is that the spinal centres have Sensibility\nof the same _order_ as the cerebral centres; and that in the normal\norganism this Sensibility enters as a factor into the general\nConsciousness--no one portion of the nervous system being really\nindependent of all the others, all co-operating in every result. Over\nand over again I have had to insist that the property of Sensibility\nis only the general condition of Sensation; and that each particular\nsensation receives its _character_ from the organs innervated, _plus_\nthe reaction of the whole organism. Obviously, therefore, the peculiar\ncharacter of a sensation, or \u201cstate of consciousness,\u201d must vary with\nthe variations in either of these factors. To say that every segment of\nthe spinal cord has Sensibility, is not saying that an excitation of\nthat segment will produce a particular sensation of definite character;\nbecause for this definite character there is needed the co-operation of\nall those parts of the mechanism which enter into the complex product.\n\n       *       *       *       *       *\n\n93. And here attention must be called to a double fallacy pervading\nthe arguments on the other side. It is always assumed that the\nreactions of an organ, or part of the organism, when separated from\nthe rest, are typical of their reactions when forming constituents\nof the normal organism. Nothing of the kind. The movement of a\nmuscle or a limb separated from the body may resemble that movement\nwhen normally effected--but only as the movements of a mechanical\nbird resemble those of a living bird: the modes of production are\ndifferent. So that were we to grant the postulate of the brain\nbeing the exclusive seat of sensation, we should still deny that an\naction which was effected after removal of the brain was typical of\nthe action effected when the brain was present. The leg of Hunter\u2019s\npatient jerked when the skin was irritated; but this action could not\nbe altogether the same as the similar action in a leg united with the\nrest of the sensitive mechanism. Nor is this all. The leg may have\nbeen insensible, the spinal segment which innervated it may have been\nwholly without Sensibility, and still we should have to question the\nlogic which extended such an inference to the very different and far\nmore complex actions of decapitated animals. On this ground:--The\nleg is, by the hypothesis, insensible because cut off from all\nconnection with the sensitive mechanism. But this is not the case\nwith the decapitated animal: there still remain the essential parts\nof a sensitive mechanism--all the chief organs are still in activity,\nstill manifesting their functions. Decapitation has produced a great\ndisturbance in the mechanism, and has removed an important centre; but\nnevertheless every impression excites a connected group of centres, and\nthis group responds.\n\n       *       *       *       *       *\n\n94. In conclusion, unless we adopt the opinion that\nSensation--Consciousness--Sensibility, is something not belonging to\nthe physiological properties of the nervous system in a vital organism\n(the opinion held by spiritualists), there seems no alternative but\nto adopt the opinion advocated in this volume, namely, that the\nphysiological properties of the nervous system are inseparable from\nevery segment of that system; and the functions are the manifestation\nof those properties as determined by the special organs with the\nco-operation of all.\n\n\n\n\nFOOTNOTES\n\n\n[1] WORDSWORTH.\n\n[2] Crystals not only grow by assimilation, but even repair injuries,\nwith a certain superficial resemblance to the repair of animal tissues.\nThus, according to the experiments of JORDAN cited by Sir JAMES PAGET\n(_Lectures on Surgical Pathology_, I. 153, and 2d ed. p. 115), an\noctohedral crystal of alum, if fractured and replaced in a motherlye\nwill in a few days exhibit a complete restoration of the original form.\nThe whole crystal increases, but the increase is greatest on the broken\nedge, and the octohedral form is completely renewed. (Comp. \u00a7 113.)\n\n[3] Cited by DRYSDALE, _Life and the Equivalence of Force_, Part II. p.\n149.\n\n[4] RANKE, _Die Lebensbedingungen der Nerven_, 1868, p. 80.\n\n[5] \u201cIl n\u2019y a peut \u00eatre pas un seul ph\u00e9nom\u00e8ne chimique dans l\u2019organisme\nqui se fasse par les proc\u00e9d\u00e9s de la chimie de laboratoire; en\nparticulier il n\u2019y a peut \u00eatre pas une oxydation qui s\u2019accomplisse par\nfixation directe d\u2019oxyg\u00e8ne.\u201d--CLAUDE BERNARD.\n\n[6] Dr. MADDEN, in his essay _On the Relation of Therapeutics to\nMedicine_, 1871, p. 5, gives a remarkable illustration of what may be\ncalled the frustration of chemical affinity effected by mechanical\nconditions. \u201cBefore calico can be printed, every loose particle of\ncotton must be removed from the surface in order that the colored inks\nmay not run. This removal is effected by passing the calico over and in\ncontact with a red-hot iron cylinder, and by regulating the rapidity\nwith which the cylinder revolves, the intense heat burns off the loose\nfibres, yet does no injury to the woven cloth. In other words, the\nchanges in the relation of the high temperature and the cotton are\ntoo rapid to admit of the fibre combining with the oxygen. Let the\nrate of revolution be reduced but very little, and the calico would\nburst into flames.\u201d Any one who has snuffed a candle with his fingers\nwill understand this. Dr. Madden further instances certain fulminates\nwhich can be detonated in contact with gun-cotton without causing it\nto explode--the extreme rapidity with which the fulminates expand is\ntoo great to enable the gun-cotton to adjust its movements to this new\nmotion. Precisely the same kind of thing occurs in organized matter. If\nthe rate of its changes be reduced below a certain point, the ordinary\nchemical affinities will assert themselves.\n\n[7] I am often reminded of the surprising movements of particles of\ncarbonate of lime in water which my friend Professor PREYER showed\nme during a visit to Bonn. He had removed one of the concretions,\nusually found in connection with nerves along the spine of old frogs,\nand crushed it in water; under the microscope the seeming spontaneity\nand variety of the movements of the particles was such that had we\nnot known their origin we should certainly have attributed them to\nvitality: no infusoria could have moved with more seeming spontaneity.\nIt is hardly physiological to conclude that because fragments of tissue\nmanifest amb\u0153biform movements therefore they are alive (STRICKER,\nart. _Die Zelle_ in his _Handbuch der Lehre von den Geweben_, 1868,\np. 7), or that the heart removed from the body is _alive_ because it\nstill beats. LIEBERK\u00dcHN, _Ueber Bewegungserschsinungen der Zellen_,\n1870, pp. 357\u2013359, cites examples of such movements in undeniably dead\nsubstances. For Life, we demand not only Movement, but Functional\nActivity.\n\n[8] TELESIUS, _De Natura Rerum_, 1586, V. 184. TELESIO might have been\nsaved from the mistake had he attended to what NIPHUS had said on\nthe point in his _Expositio subtilissima_, 1559, p. 245. Comp. also\nPHILELPHUS, _Epist. Familiarum_, 1502, p. 253, _verso_.\n\n[9] The authorities just cited are ARISTOTLE, _De Anima_, Lib.\nII. c. I. KANT, _Kritik der Urtheilskraft_. M\u00dcLLER, _Physiology_.\nBEALE, _Bioplasm_, and _Introduction to Todd and Bowman\u2019s Anatomy_.\nSCHELLING, _Erster Entwurf_, and _Transcendent. Idealismus_. BICHAT,\n_Recherches sur la Vie et la Mort_. STAHL, _Theoria Vera Medica_.\nDUG\u00c8S, _Physiologie Compar\u00e9e_. B\u00c9CLARD, _Anatomie G\u00e9n\u00e9rale_. LAMARCK,\n_Philosophie Zoologique_. COMTE, _Cours de Philosophie Positive_.\nOWEN\u2019S _Hunterian Lectures_, 1854. HERBERT SPENCER, _Principles of\nBiology_.\n\n[10] FLETCHER, as quoted by DRYSDALE, _Life and the Equivalence of\nForce_, Part II. p. 120.\n\n[11] ROBIN et VERDEIL, _Trait\u00e9 de Chimie Anatomique_, 1853.\n\n[12] PAGET, _Lectures on Surgical Pathology_, p. 14.\n\n[13] Comp. HAECKEL, in _Siebold und K\u00f6lliker\u2019s Zeitschrift_, 1865, p.\n342, and his _Generelle Morphologie_, 1866, I, 135, 336.\n\n[14] In the _Archiv f\u00fcr mikros. Anatomie_, 1865, p. 211.\n\n[15] Here organization is the simplest form of all--molecular organized\nstructure, which in the higher forms becomes tissue structure,\nand organ structure. The word _structure_ properly means orderly\narrangement of different materials; and molecular structure refers\nto the different proximate principles which constitute the organized\nsubstance. Usually, however, the word _structureless_ indicates the\nabsence of _visible_ arrangement of the parts; a cell has structure\nsince it has nucleus and protoplasm.\n\n[16] In the cell-theory established by SCHLEIDEN and SCHWANN, in 1838,\nand which has formed the basis of modern histology, the cell-wall\nwas endowed with an importance which can no longer be upheld now\nthat the existence of independent organisms, and of cells, without\na trace of enveloping membrane has been abundantly observed. Cells\nwithout walls were first described by COSTE in the _Comptes Rendus_,\n1845, p. 1372. They were also described by CHARLES ROBIN in 1855,\n_Dict. de la M\u00e9dicine_, art. _Cellule_. But little notice was taken\nuntil MAX SCHULTZE, in his famous essay, _Ueber Muskelk\u00f6rperchen\nund was man eine Zelle zu nennen habe_, which appeared in _Reichert\nund Du Bois Reymond\u2019s Archiv_, 1861,--BRUECKE, in his memoir, _Die\nElementarorganismen_, 1861,--and LIONEL BEALE, in his _Structure of the\nSimple Tissues_, 1861,--all about the same time began the reform in\nthe cell-theory which has effected a decisive change in the classical\nteaching. LEYDIG claims, and with justice, to have furnished important\ndata in this direction (_Vom Bau des thierischen_ _K\u00f6rpers_, 1864, I.\np. 11). The student interested in this discussion should consult MAX\nSCHULTZE, _Das Protoplasma der Rhizopoden und der Pflanzenzellen_,\n1863; HAECKEL, _Die Radiolarien_, 1862; the controversial papers by\nREICHERT, in his _Archiv_ (beginning with the Report of 1863), and MAX\nSCHULTZE, in his _Archiv f\u00fcr mikros. Anat._, with HENLE\u2019S judgment in\nhis _Jahresberichte_, and K\u00dcLLIKER\u2019S summing-up in the last edition of\nhis _Gewebelehre_. For a full yet brief history of the cell-theory see\nDRYSDALE, _The Protoplasmic Theory of Life_, 1874, pp. 96\u2013106.\n\n[17] At the time this was written, I had some fish ova in the course\nof development. Out of the same mass, and in the same vessel, all\nthose which were supported by weed at a depth of half an inch from\nthe surface, lived and developed; all those, without exception, that\nwere at a depth of two to four inches, perished. In ordinary parlance,\nsurely, nothing would be objected to in the phrase, \u201cthese ova were\nall in the _same_ Medium\u201d; the water was the same, the weed the same,\nthe vessel the same; yet some difference of temperature and carbonic\nacid made all the difference between life and death. Another curious\nfact was observed; I removed eight of these ova with active embryos,\nand placed them in a large watch-glass containing a solution (one half\nper cent) of bichromate of ammonia. In this acid the embryos lived\nand were active fifty-seven hours, although other embryos placed in a\nsimilar watch-glass containing pond-water, survived only forty hours.\nThe non-effect of the acid was probably due to the non-absorption\nwhich nullifies the effect of certain virulent poisons when they are\nswallowed; but why the fish should live longer in the acid than in the\nsimple water, I do not at all comprehend.\n\n[18] AGASSIZ, _Essay on Classification_, 1859, p. 15.\n\n[19] HAECKEL, _Generelle Morphologie_, II. 211.\n\n[20] See on this last point RANKE, _Die Lebensbedingungen der Nerven_,\n1868, p. 34.\n\n[21] See WALDEYER, art. _Eierstock_, in STRICKER\u2019S _Handbuch der Lehre\nvon den Geweben_, 1870, p. 570. \u201cI found in a f\u0153tus, which, in a case\nof extra-uterine pregnancy, had lain thirty years in the body of its\nmother, the structure of the muscles as intact as if it had been born\nat its full time.\u201d--VIRCHOW, _Cellular Pathologie_, Lect. XIV.\n\n[22] See BEALE, _The Structure of the Simple Tissues_, 1861; the\nIntrod. to his edition of _Todd and Bowman\u2019s Physiological Anatomy_,\n1866; and _How to Work with the Microscope_, 4th ed., 1868; also\n_Bioplasm_, 1872.\n\n[23] \u201cThe physical property of the tissue does not depend upon this\nmatter, _nor is its function due to it_.\u201d--Beale, _Introduction to Todd\nand Bowman_, p. 11. That is to say, he regards even contractility and\nneurility as physical, not vital facts.\n\n[24] In turning over the pages of a work which was celebrated some\nhalf-century ago--RUDOLPHI\u2019S _Grundriss der Physiologie_--I was\ninterested to find a clear recognition of this biological principle:\n\u201cAlle Theile aller Organismen,\u201d he says, I. 233, \u201csie m\u00f6gen noch so\nverschieden in ihrem Bau, in ihrer Mischung, und in ihrer Th\u00e4tigkeit\nseyn, sind ohne Ausnahme _als organisch und mithin als lebend zu\nbetrachten_.\u201d In a note he adds that physiologists have considered\ncertain solid parts--epidermis, nail, hair, and bones--to be dead; \u201cbut\nall these are organically developed, and are in direct connection with\nthe other parts.\u201d\n\n[25] VIRCHOW, _Die Cellular Pathologie_, 1860, Lect. I.\n\n[26] BEALE, _Bioplasm_, 104.\n\n[27] K\u00d6LLIKER, _Gewebelehre_, 5th ed., 1867, p. 12.\n\n[28] Nevertheless there are some facts directly contradicting his\nconclusions. For example, he considers the axis cylinder of the nerve\nto be formed material, and agrees with MAX SCHULTZE and others as to\nits fibrillated structure; yet according to LISTER and TURNER, GERLACH\nand FREY, the axis cylinder is deeply stained by carmine, and in this\nrespect resembles the nucleus of protoplasm.\n\n[29] From the quite recent experiments M. BAILLON has submitted to the\n_Acad\u00e9mie des Sciences_ (15th February, 1875), it appears that although\ncut flowers absorb colored fluids, the roots when intact only absorb\nthe fluid, and reject the coloring matters, by a veritable dialysis.\n\n[30] GERLACH cited by RANKE, _op. cit._, p. 76.\n\n[31] STEIN, _Der Organismus der Infusionsthierchen_, 1859, p. 76.\n\n[32] STAHL had a profound conviction of the radical difference,\nthough he was not able to point out the conditions involved. See his\n_Disquisitio de mechanismi et organismi vera diversitate_.\n\n[33] M. FERNAND PAPILLON has shown that animals may be fed with food\ndeprived of phosphates of lime if its place is supplied with magnesia,\nstrontia, or alumina; they make their bones out of these as out of\nlime. But no such substitution is possible in muscle, nerve, or gland;\nwe cannot replace the phosphate of magnesia in muscles by the phosphate\nof iron, lime, or potash, as we can replace the iron of a wheel by\nsteel, copper, or brass.\n\n[34] Anatomy resolves the Tissues into Organites (cells, fibres,\ntubes); here its province ends, and that of Chemistry begins by\npointing out the molecular composition of the Organites.\n\n[35] This luminous conception, though vaguely seized by PINEL, was\nfirst definitely wrought out by BICHAT. See his _Recherches sur la Vie\net la Mort_--and especially his _Anatomie G\u00e9n\u00e9rale_, 1812, I. p. lxx.\nIt was one of the most germinal conceptions of modern times.\n\n[36] Just as there go other materials besides canvas to make a sail,\nand others besides iron to make a windlass, so there go other tissues\nbesides the muscular to form a muscle--there is the membranous\nenvelope, the nerve, the blood-vessels, the lymphatics, the tendon, and\nthe fat. Even in Contraction there is another property involved besides\nthe Contractility of the muscular element, namely, the Elasticity\nof the fibrous wall of the muscular tube; but Contractility is the\ndominant property, and determines the speciality of the function.\n\n[37] \u201cL\u2019\u00e9l\u00e9ment musculaire peut \u00eatre annex\u00e9 \u00e0 une foule de m\u00e9canismes\ndivers; tant\u00f4t \u00e0 un os, tant\u00f4t \u00e0 un intestin, tant\u00f4t \u00e0 une vessie,\ntant\u00f4t \u00e0 un vaisseau, tant\u00f4t \u00e0 un conduit excr\u00e9teur, tant\u00f4t enfin \u00e0 des\nappareils tout \u00e0 fait sp\u00e9ciaux \u00e0 certaines esp\u00e8ces d\u2019animaux.\u201d--CLAUDE\nBERNARD, _Rapport sur les Progr\u00e8s de la Physiologie g\u00e9n\u00e9rale_, 1867, p.\n38.\n\n[38] VULPIAN, _Le\u00e7ons sur la Physiologie du Syst\u00e8me Nerveux_, 1866,\np. 581. In a work just published I find M. LUYS hesitating at the\nconsistent application of this law. After pointing out the identity\nof the tissue in cerebrum and spinal cord, he is only prepared\nto say that we cannot deny that there is _no impossibility_ in\nadmitting physiological equivalence where there is morphological\nequivalence.--LUYS, _Actions Reflexes du Cerveau_, 1874, p. 14.\n\n[39] It is because men converted the result into a principle, and\nsupposed that Life preceded the Organism, that they were led to puzzle\nthemselves over such facts as the continuance of vitality in divided\norganisms. ARISTOTLE felt the force of the objection: \u201cPlants when\ndivided are seen to live, and so are certain insects, as if still\npossessing the same Vital Principle (\u03c8\u03c5\u03c7\u03ae) considered specifically\n(\u03c4\u1ff7 \u03b5\u1f34\u03b4\u03b5\u03b9) though not the same numerically (\u03bc\u1f74 \u1f00\u03c1\u03b9\u03b8\u03bc\u1ff7). Each of these\nparts has sensation and locomotion for a time; and there is no room for\nsurprise at their not continuing to manifest these properties, seeing\nthat the organs necessary for their preservation are absent.\u201d--_De\nAnima_, Lib. I. Ch. IV. Compare BASSO, _Philos. Naturalis adversus\nAristotelem_, Amsterdam, 1649, p. 260; and TAURELLUS, _Contra\nC\u00e6salpinum_, 1650, p. 850; neither of them grappling with the\ndifficulty so firmly as ARISTOTLE.\n\n[40] SPENCER, _Principles of Biology_, 1864, I. 153.\n\n[41] Comp. LAMARCK, _Philos. Zool._, II. 114.\n\n[42] Comp. SPENCER, _op. cit._, II. 362, 363, for good illustrations of\nthis.\n\n[43] AGASSIZ, _Essay on Classification_, p. 91.\n\n[44] \u201cNulla in corpore animali para ante aliam facta est, et omnes\nsimul creat\u00e6 exiatunt.\u201d--HALLER, _Elementa Physiologi\u00e6_, VIII. 148.\n\n[45] QUATREFAGES, _Metamorphoses de l\u2019Homme et des Animaux_, 1862, p.\n42.\n\n[46] VON BAER, _Ueber Entwickelungageschichte_, 1828, I. 221.\n\n[47] Curiously enough, while the Nudibranch, which is without a shell,\npossesses one during its embryonic life, there is another mollusc,\n_Neritina fluviatilis_, which possessing a shell in its subsequent life\nis without one during the early periods, and according to CLAPAR\u00c8DE\nbegins an independent existence, capable of feeding itself before it\nacquires one. See his admirable memoir on the _Neritina_, in _M\u00fcller\u2019s\nArchiv_, 1857.\n\n[48] Has any advocate of the hypothesis that animals were created as\nwe see them now, fully formed and wondrously adapted in all their\nparts to the conditions in which they live, ever considered the hind\nlegs of the seal, which he may have watched in the Zo\u00f6logial Gardens?\nHere is an animal which habitually swims like a fish, and cannot use\nhis hind limbs except as a rudder to propel him through the water; but\ninstead of having a fish-like tail he has two legs flattened together,\nand nails on the toes--toes and nails being obvious superfluities. Now\nwhich is the more rational interpretation, that these limbs, in spite\nof their non-adaptation, were retained in rigid adherence to a Plan, or\nthat the limbs were inherited from an ancestor who used them as legs,\nand that these legs have gradually become modified by the fish-like\nhabits of the seal?\n\n[49] MILNE EDWARDS, _Intro. \u00e0 la Zoologie G\u00e9n\u00e9rale_, 1851, p. 9.\n\n[50] VON BAER, _op. cit._, I. 203.\n\n[51] WOLFF, _Theorie der Generation_, 1764, \u00a7 67. The reader will find\nabundant and valuable corroboration of this biological principle in SIR\nJAMES PAGET\u2019S _Lectures on Surgical Pathology_.\n\n[52] VON BAER, _Selbstbiographie_, 1866, p. 319.\n\n[53] MILNE EDWARDS, _Intro. \u00e0 la Zoologie G\u00e9n\u00e9rale_, 176.\n\n[54] VON BAER, _Ueber Entwickelungsgeschichte_, I. 147.\n\n[55] LOTZE, art. _Lebenskraft_, in _Wagner\u2019s Handw\u00f6rterbuch der\nPhysiologie_, p. XXVI.\n\n[56] I had kept these tritons four years in the hope that they would\nbreed; but in spite of their being subjected to great varieties of\ntreatment--for months well supplied with food, and for months reduced\nalmost to starvation--they never showed the slightest tendency to\nbreed; another among the many illustrations of the readiness with which\nthe generative system is affected even in very hardy and not very\nimpressionable animals. CLAPAR\u00c8DE observed the still more surprising\nfact that the _Neritina fluviatilis_ (a river snail) not only will not\nlay eggs, but will not even feed in captivity. He attributes it to the\nstillness of the water in the aquarium, so unlike that of the running\nstreams in which the mollusc lives. See _M\u00fcller\u2019s Archiv_, 1857.\n\n[57] BRONN, _Morphologische Studien \u00fcber die Gestaltungs-Gesetze_,\n1858. Compare the note on \u00a7 11.\n\n[58] DARWIN, _On Domestication_, II. 340. In the _Annales des\nSciences_, 1862, p. 358, M. MALM describes a fish in his collection,\nthe tail of which had been broken, and the bone which grew out at the\ninjured spot had formed a second tail with terminal fin.\n\n[59] In the memoir on the _Anatomy and Physiology of the Nematoids_,\nby Dr. CHARLTON BASTIAN, which appeared in the _Philosophical\nTransactions_ for 1866, we read that even these lowly organized\nworms have little power of repair. Speaking of the \u201cpaste eels\u201d\n(_Anguilulid\u00e6_), he says, \u201cI may state as the result of many\nexperiments with these that the power they possess of repairing\ninjuries seems very low. I have cut off portions of the posterior\nextremity, and though I watched the animal for days after, could never\nrecognize any attempt at repair.\u201d Perhaps, however, the season may have\nsome influence; and Dr. WILLIAMS\u2019S denial respecting the Na\u00efs may be\nthus explained. [What is said above was written in 1868, and published\nin the June number of the _Fortnightly Review_. In the August of that\nyear the question of reproduction of lost limbs was treated by Prof.\nROLLESTON in his _Address to the British Medical Association_, in which\nhe showed cogent evidence for the conclusion that the reproduction\nof limbs only exists is animals that have feeble respiration, and\nconsequently slow vital processes.]\n\n[60] This beautiful and transparent larva reminds one in many respects\nof the Pike as it poises itself in the water awaiting its prey. It is\nenabled to do so without the slightest exertion by the air-bladders\nwhich it possesses in the two kidney-shaped rudiments of trache\u00e6, and\nwhich in the gnat become developed into the respiratory apparatus. The\nresemblance to the air-bladder of fishes is not simply that it serves\na similar purpose of sustaining the body in the water, it is in both\ncases a rudiment of the respiratory apparatus, which in the fish never\nbecomes developed. WEISMANN calls attention to an organ in the larv\u00e6 of\ncertain insects (the _Culicid\u00e6_), which have what he calls a tracheal\n_gill_, which gill has this striking analogy with the fish-gill that\nit separates the air from the water, and not, as a trachea, direct\nfrom the atmosphere. See his remarkable memoir _Die nachembryonale\nEntwickelung des Muscidens_, in _Siebold und K\u00f6lliker\u2019s Zeitschrift_,\n1864, p. 223.\n\n[61] _The Variation of Animals and Plants_, 1868, II. p. 272.\n\n[62] _Origin of Species_, 5th ed. p. 96.\n\n[63] Mr. Darwin has himself, in the following passage, stated a\nsomewhat similar view, and rejected it: \u201cIn one sense the conditions of\nlife may be said not only to cause variability, but likewise to include\nNatural Selection, for _the conditions determine whether this or that\nvariety shall survive_. But when man is the selecting agent, we clearly\nsee that the two elements of change are distinct; the conditions\ncause the variability, the will of man acting either consciously or\nunconsciously accumulates the variations in certain directions, and\nthis answers to the survival of the fittest under nature.\u201d (p. 168.)\n\n[64] Even in the nerve-sheaths of some Annelids there are muscles.\n\n[65] SPENCER, _Principles of Biology_, II. 72\n\n[66] FAIVRE, _Variabilit\u00e9 de l\u2019Esp\u00e8ce_, p. 15.\n\n[67] These luminous organs would furnish an interesting digression\nif space permitted it. The student is referred to the chapter in\nMILNE EDWARDS\u2019S _Le\u00e7ons sur la Physiologie et l\u2019Anatomie Compar\u00e9e_,\n1863, VIII. 94, sq. LEYDIG, _Histologie_, 1857, p. 343. K\u00d6LLIKER,\n_Microscopical Journal_, 1858, VIII. 166, and MAX SCHULTZE, _Archiv\nf\u00fcr mikros. Anat._, 1865, p. 124. My friend SCHULTZE was kind enough\nto show me some of his preparations of the organs of _Lempyris\nsplendidula_, from which the drawings in his memoir were made.\nThey reminded me of the electric organs in fishes by a certain\nfaint analogy, the trachea in the one holding the position of\nnerves in the other. I may remark, in passing, that it is not every\nphosphorescent animal that has distinct luminous organs. There is a\nlizard (_Pterodactylus Gecko_) which occasionally becomes luminous. \u201cA\nsingular circumstance occurred to the colonial surgeon, who related it\nto me. He was lying awake in bed when a lizard fell from the ceiling\nupon the top of his mosquito-curtain; at the moment of touching it the\nlizard became brilliantly luminous, illuminating the objects in the\nneighborhood, much to the astonishment of the doctor.\u201d COLLINGWOOD,\n_Rambles of a Naturalist_, 1868, p. 169.\n\n[68] MAX SCHULTZE, _Zur Kenntniss der electrischen Organe der Fische_,\n1858\u20139.\n\n[69] LEYDIG, _Histologie_, 1857, p. 45.\n\n[70] OWEN, _Anatomy of The Vertebrates_, 1866, I. 358.\n\n[71] DAVY, _Researches, Physiological and Anatomical_, 139, I. 33.\n\n[72] \u201cIf it could be demonstrated that any complex organ existed\nwhich could not possibly have been formed by numerous successive\nslight modifications, my theory would absolutely break down.\u201d--DARWIN,\n_Origin of Species_, 5th ed. p. 227. In several passages insistence\nis made on this. \u201cNatura non facit saltum\u201d may be perfectly true; but\nwithout impugning the Law of Continuity we may urge that the Law of\nDiscontinuity is equally true. The one is an abstract ideal conception;\nthe other is a concrete ideal conception. According to the one, every\nchange from rest to motion, or from one state to another, must pass\nthrough infinites; according to the other every change is abrupt.\nIn my First Series, Vol. I. p. 327, I have shown how, on mechanical\nprinciples, every change in an organism must be abrupt. A glance at\nthe metamorphoses of the embryo, or the stages of insect-development,\nwill show very sudden and abrupt changes. Let me also cite Mr. Darwin\nagainst himself: \u201cWhen we remember such cases as the formation of\nthe more complex galls, and certain monstrosities, which cannot be\naccounted for by reversion, cohesion, etc., and _sudden, strongly\nmarked deviations of structure_, such as the appearance of a moss-rose\non a common rose, we must admit that the organization of the individual\nis capable through _its own laws of growth, under certain conditions_,\nof undergoing great modifications, independent of the gradual\naccumulation of slight inherited modifications.\u201d--_Origin_, p. 151. See\nalso note to \u00a7 130, further on, p. 142.\n\n[73] On the Nutrition of Monads, see the remarkable memoir by\nCIENKOWSKI, in the _Archiv f\u00fcr mikros. Anatomie_, I. 221, sq.\n\n[74] PAGET, _Lectures on Surgical Pathology_, edited by TURNER, 1865,\np. 19.\n\n[75] It has recently been shown that certain Crustacea vary not only\nfrom species to species, but from genus to genus, when living in\nwater of different degrees of saltness. By continued dilution of the\nsalt water an _Artemia_ was developed into another species, and this\nagain into a _Branchipus_--a genus of large dimensions, with an extra\nabdominal segment, and a different tail; a genus, moreover, which is\npropagated sexually, whereas the _Artemia_ is parthenogenetic, as a\nrule. See _Nature_, 1876, June 8, p. 133.\n\nThe exceeding importance of this fact is, that it proves specific\nand even generic differences to originate simply through the gradual\nchanges of the medium and the adaptation of the organism to these new\nconditions. It also disproves the very common notion--adopted even\nby Mr. DARWIN himself--that \u201corganic beings must be exposed _during\nseveral generations_ to new conditions to cause any appreciable amount\nof variation.\u201d Again, \u201cNatural Selection, if it be a true principle,\nwill banish the belief of any great and sudden modification of\nstructure.\u201d--Comp. note to \u00a7 121, p. 132.\n\n[76] Compare LEYDIG, _Vom Bau des thierischeu K\u00f6rpers_, 1864, p. 27.\n\n[77] FERDINAND COHN, _Die contractile Gewebe im Pflanzenreich_, 1862.\nBy a series of numerous well-devised experiments, Cohn found that in\nthe stamen of the _centauria_ a tissue exists which is excitable by the\nsame stimula as muscle is, and which reacts like muscle, describing a\nsimilar curve when excited, and, after reaching its maximum, relaxing.\nLike the muscle it becomes fatigued by repeated contraction, and\nrecovers its powers by repose. Like the muscle it may be rendered\ntetanic. (The researches of Dr. BURDON SANDERSON and Mr. DARWIN have\nsince placed beyond a doubt the Contractility and Sensibility of\ncertain plants.)\n\n[78] MIVART, _The Genesis of Species_, 1871, p. 23.\n\n[79] DOHRN, _Der Ursprung der Wirbelthiere und das Princip des\nFunctionswechsels_, 1875, p 74.\n\n[80] SIGMUND MAYER, _Die peripherische Nervenzelle und die sympathische\nNervensystem_, 1876.\n\n[81] On these cells see note to \u00a7 140.\n\n[82] These terms designate the surface aspect of a transverse section,\nof what more correctly should be called the gray columna. See Figs.\u00a03\nto 6.\n\n[83] But this only in the higher animals. In reptiles and amphibia the\nmedulla descends into the cervical region, as far as the second and\nthird cervical vertebr\u00e6. This should be remembered in experimenting.\n\n[84] FOSTER and BALFOUR, _Elements of Embryology_, Part I., 1874. Comp.\nSCHWALBE, art. _Die Retina_, in the _Handbuch der Augenheilkunde_ of\nGRAEFE _and_ S\u00c4MISCH, 1874, I. 363.\n\n[85] The development of the olfactory lobe and bulb is similar; it need\nnot be followed here.\n\n[86] German anatomists divide this axis into trunk and crown\n(_Hirnstamm_ and _Hirnmantel_). There is convenience in this division.\nIf we remove all the gray matter of the cerebrum, with all the white\nmatter radiating from it, until we again come upon gray matter--and\nif we then cut the cerebellum from its descending strands of white\nmatter--we shall have removed the _crown_, and leave the _trunk_\nremaining. This trunk is constituted by the corpora striata, nucleus\nlentiformis, optic thalami, corpora quadrigemina, crura cerebri, pons,\nmedulla oblongata, and medulla spinalis. From this trunk all the organs\nof the body are directly innervated (except those innervated from the\nsympathetic?).\n\n[87] \u201cOn s\u2019est pr\u00e9occup\u00e9 du r\u00f4le sp\u00e9cial que pouvaient jouer les\nganglions p\u00e9riph\u00e9riques situ\u00e9s dans le voisinage de certaines organes;\net on a pr\u00e9tendu que les nerfs ne jouissaient de leur propri\u00e9t\u00e9 d\u2019agir\nsur ces organes qu\u2019apr\u00e8s avoir travers\u00e9 ces ganglions. On avait admis\nque l\u2019excitation port\u00e9e sur le filet nerveux avant son entr\u00e9 dans le\nganglion restait sans effet; que pour obtenir l\u2019action excitatrice\ndes fonctions de l\u2019organe il fallait exciter le nerf entre lui et le\nganglion voisin.\u201d--CLAUDE BERNARD, _Syst\u00e9me Nerveux_, II. 169. But on\nproceeding to verify these statements by experiment, BERNARD is led to\nthe conclusion, \u201cque le ganglion n\u2019a pas d\u2019influence propre sur le mode\nde l\u2019excitation transmise \u00e0 l\u2019organe.\u201d\n\nI was delighted to find my opposition to the current teaching\nrespecting the central functions of ganglionic cells thoroughly\nborne out by the elaborate researches of SIGMUND MAYER (_Archiv f\u00fcr\nPsychiatrie_, Bd. VI. Heft 2). Having artificially produced such cells,\nhe pertinently asks, How can we attribute central functions to cells\nwhich appear in the process of regeneration of a divided nerve! The\nerror has its origin in the confusion of functions with properties.\n\n[88] It is often, though incorrectly, stated that every segment of an\nannulose animal has its separate ganglion. The fact is, that while the\nganglia are usually fewer than the segments, they are sometimes more\nnumerous.\n\n[89] It has been proved that the cells of the cornea and the pigment\ncells of the skin contract under nervous excitation. We cannot suppose\nthat although these are the only cells which have hitherto been brought\nunder experimental observation, they are the only cells subject to\nnerve-influence. We may safely assume that wherever a nerve-fibre\nterminates, its action will be transformed into an excitation of the\npart. Habitually, however, motor-nerves are spoken of as muscle-nerves.\n\n[90] On Deduction, see _Problems: First Series_, Vol. II. p. 159\n\n[91] I do not here touch upon the question as to whether these actions\nof the senses are _sensations_, because that question demands that\nwe should first settle what is _Sensation_. I may at once, however,\nsay that what is ordinarily understood as a sensation of _color_,\nor a sensation of _sound_, is, in my opinion, not possible without\nthe cerebrum. But the sensibility of the eye and ear is manifestly\npreserved.\n\n[92] It has been observed that removal of the cerebellum affects the\npigment cells of the skin. No doubt other parts are also affected, but\nthe changes have hitherto escaped observation.\n\n[93] OWSJANNIKOW describes the results of removing carefully the\ncranial ganglia of the crayfish; and these effects MEYER observes to\nbe identical with those which follow removal of the large claw of\nthe crayfish! A. B. MEYER, _Das Hemmungsnerven-system des Herzens_,\n1869, p. 23. Let me add that the phenomena described by M. FAIVRE\nas following the destruction of one sub\u0153sophageal ganglion in the\n_Dytiscus_, are so little to be referred to the mere absence of the\nganglion, that I find them not to occur when the whole head is removed.\n\n[94] PFL\u00dcGER, _Die Sensorischen Funktionen des R\u00fcckenmarks_,1858.\nAUERBACH, _G\u00fcnzburg\u2019s Zeitschrift_. Jahrgang IV. p. 486. LEWES, _Leeds\nMeeting of British Association_, 1858, and _Physiology of Common Life_,\n1860.\n\nThis recognition of sensation, and even of volition, in spinal actions\nmay be found in the writings of WHYTT, UNZER, PROCHASKA, LEGALLOIS, and\nMAYO; but the establishment of the Reflex Theory had displaced it, and\nits revival dates from PFL\u00dcGER.\n\n[95] FRIEDL\u00c4NDER (_Versuch \u00fcber die innern Sinne_, 1826, I.\n77) declares it to be a rational necessity: \u201cDie Annahme eines\nNervenfluidums ist Nothwendigkeit der Vernunft.\u201d\n\n[96] These terms and the conception they embody were proposed by me in\n1859 in a paper \u201cOn the necessity of a reform in Nerve-physiology,\u201d\nread at the Aberdeen meeting of the British Association, and were\nreproduced in the _Physiology of Common Life_. (Prof. OWEN, probably\nin forgetfulness of my suggestion, proposed \u201cneuricity.\u201d _Lectures\non the Comp. Anat. of Vertebrates_, 1866, I. p. 318.) The terms were\nfortunate enough to meet with acceptance from some physiologists\nboth in England and France; and the conception has been more widely\naccepted than the terms. The most distinguished approver was Prof.\nVULPIAN. \u201cFaute d\u2019une meilleure d\u00e9termination on peut, avec M. Lewes,\ndonner \u00e0 la propri\u00e9t\u00e9 physiologique des fibres nerveuses le nom de\n_neurilit\u00e9_; c\u2019est l\u00e0 ce qui correspondra \u00e0 la oontractilit\u00e8 des fibres\nmusculaires.\u201d _Le\u00e7ons sur la physiologie du syst\u00e8me nerveux_, 1866, p.\n220. He also adopted my suggestion (since modified) of Sensibility as\nthe property of ganglionic cells. Compare also GAVARRET, _Ph\u00e9nom\u00e8nes\nphysiques de la Vie_, 1869, pp. 213 and 222. TAULE, _Notions sur la\nnature de la mati\u00e8re organis\u00e9e_, 1866, p. 131. CHARLES ROBIN, _Anatomie\net physiologie cellulaires_, 1873, p. 166.\n\nBy these channels, and by the German, Italian, Russian, Polish, and\nHungarian translations of my work, the suggestions were carried over\nEurope, crept into scientific journals, and became known to writers who\nnever heard of me. I only mention these facts lest the reader should\nsuppose that my views had been anticipated by certain continental\nwriters.\n\n[97] \u201cLa force nerveuse n\u2019existe pas comme puissance independant des\npropri\u00e9t\u00e9s de tissu. Elle consiste en l\u2019action des parties excit\u00e9s, sur\nles parties excitables, l\u2019\u00e9tat de l\u2019excitation des premi\u00e8res agissant\ncomme impression ou stimulation sur les secondes.\u201d--LANDRY, _Trait\u00e9 des\nParalysies_, 1859, I. 142.\n\n[98] \u201cLe syst\u00e8me nerveux est tout \u00e0 la fois l\u2019origine des sensations\net l\u2019origine des mouvements. Mais est-ce par une propri\u00e9t\u00e9 unique, ou\npar deux propri\u00e9t\u00e9s diverses qu\u2019il d\u00e9termine deux ph\u00e9nom\u00e8nes aussi\ndistincts!\u201d FLOURENS, _Recherches sur les propri\u00e9t\u00e9s et les fonctions\ndu Syst\u00e8me Nerveux_, 1824, p. 1. He concludes that \u201cla puissance\nnerveuse n\u2019est pas unique; il n\u2019y a pas une seule propri\u00e9t\u00e9, il y en a\ndeux,\u201d p. 24. In this he has been generally followed.\n\n[99] \u201cI have raised and stretched the thick orbital nerve of horses\non the handle of a scalpel, like a string on the bridge of a violin,\nwithout exciting the least sensation; but as soon as mechanical or\nchemical irritation had given rise to inflammation of the nerve a\ngentle touch caused violent pain.\u201d--ROMBERG, _Nervous Diseases_\n(translated for the Sydenham Society), I. 10.\n\n[100] The experiments of HALLER, _Sur la nature sensible et irritable\ndes parties_, I. 245; and the remarks of PROCHASKA, DE FUNCTIONIBUS\nSYSTEMATIS NERVOSI (translated by LAYCOCK in the volume published by\nthe _Sydenham Society_, p. 396), ought to have sufficed. See further\non, Chap. V.\n\n[101] In mammals about three days, in birds four days, in frogs\nfourteen to twenty days.\n\n[102] RUTHERFORD, in _Journal of Anatomy_, 1873, No. VIII. p. 331.\n(FLEISCHL denies that the nerve _in situ_ has different degrees of\nreaction. _Sitzungsberichte der Wiener Akad._, December, 1876.)\n\n[103] MUNK, in the _Archiv f\u00fcr Anat._, 1860, p. 798.\n\n[104] HALLER, _M\u00e9moires sur la nature sensible et irritable des\nparties_.\n\n[105] _Comptes Rendus_, 1862, LIV. p. 965.\n\n[106] \u201cJ\u2019esp\u00e8re vous convaincre que tous les \u00e9l\u00e9ments anatomiques\ndes nerfs sensitifs, moteurs, vasomoteurs, et autres, ont les\nm\u00eames propri\u00e9t\u00e9s, et ne sont distincts que par leurs fonctions.\nCette question est de la plus haute importance pour la physiologie\ng\u00e9n\u00e9rale. C\u2019est celle qui domine toute la physiologie des fibres\nnerveuses.\u201d--VULPIAN, _Le\u00e7ons sur la Physiologie du Syst\u00e8me Nerveux_,\np. 11.\n\n[107] Mr. JAMES ANDREWS.\n\n[108] In the second number of _La Revue Philosophique_, Paris, 1876, I\nhave treated this question of specific energies more at length than I\ncould find space for in the present volume.\n\n[109] In 1859 I mentioned that if the nerves of a frog\u2019s back be\nexposed by raising the skin, they may be pricked or even cut without\nsensible effect, although a slight prick on the skin will excite the\nnerves, and cause a reflex action. In 1870, Prof. FICK expressed his\nastonishment at finding that after he had cut out a piece of the\nskin, leaving it attached to the body by a single nerve, electrical\nstimulation of this excised skin caused the frog to make the reflex\nmovement of rubbing the irritated surface; whereas electrical\nstimulation of the nerve-trunk itself produced no reflex effect, only a\ntwitching of a muscle. _Pfl\u00fcger\u2019s Archiv_, 1870, p. 327. BROWN S\u00c9QUARD\ntries to establish a distinct species of nerves as _conductors_ of\nsensitive impressions, from those which are _impressionable_. The\nfacts on which he founds these two properties simply show that nerves\nare so disposed that the stimulus which excites them in one place\nfails in another. He could hardly maintain that a skin nerve contained\nimpressionable fibres at its periphery, and only conducting fibres in\nits trunk! See his communication to the Royal Society, _Proceedings_,\n1856; and _Lectures_ in the _Lancet_, 10th July, 1858.\n\n[110] In consequence of this observation some physiologists have\nmaintained that Feeling or Consciousness never arises in cerebral\nactivity, unless the thalami and the connected tracts are at the\nsame time in action. I go further, and maintain that there is no\nConsciousness (in the restricted meaning of the term) _unless the whole\norganism is involved_. Cerebral or spinal activity will be activity of\nSensibility; but this is only the basis of Consciousness.\n\n[111] \u201cAn unconscious sensation, which Lewes distinguishes\nfrom perception, is to me an inconceivable (ist f\u00fcr mich\nein Unding).\u201d--SCHR\u00d6DER VAN DER KOLK, _Die Pathologie des\nGeistes-Krankheiten_, p. 22.\n\n[112] By selective adaptation is meant the varying combination of motor\nimpulses to suit the varying requirements of the effect to be produced.\nPhysical mechanisms are limited to the performance of definite actions;\nsensitive mechanisms employ fluctuating combinations of elements in\nresponse to fluctuations of stimuli. The wheels, levers, springs, and\nvalves of a machine cannot be differently combined according to varying\ndegrees of the motor-force, as the nerves and muscles of an organism\nare differently combined by varying sensations. An automaton may be\nconstructed to play on the violin, but it will only play the air to\nwhich it is _set_; it cannot vary the performance,--cannot play a false\nnote, or throw in a _crescendo_ here, a _largo_ there, according to a\ncaprice of feeling. We must admit that violinist has his delicate and\nchanging movements guided by sensations, auditory and muscular; any\ninterruption in the sensations would arrest the movements, which in\ntruth _incorporate_ them. And yet it is well known that the violinist\nmay perform while completely \u201cunconscious.\u201d I do not simply refer to\nthe fact that his thoughts and attention may be elsewhere; I refer to\nsuch facts as are recorded in Pathology. TROUSSEAU, for example, had an\nepileptic patient who was occasionally seized with attacks of complete\nunconsciousness while he was performing in the orchestra; yet, on\nreawakening to consciousness, he found that he had continued to play,\nhad kept proper time, and played the proper notes.\n\n[113] CLAUDE BERNARD, _Syst\u00e8me Nerveux_, 1858, I. 349.\n\n[114] WORDSWORTH, _The Prelude_.\n\n[115] \u201cOn peut dire que toujours un ph\u00e9nom\u00e8ne de mouvement reconnait\npour point de d\u00e9part une impression sensitive.\u201d--CLAUDE BERNARD, I. 267.\n\n[116] Since this was written Prof. MICHAEL FOSTER and Mr. DEW SMITH\nhave published their very important researches on the motions of the\nheart, which establish beyond a doubt that, in the molluscs at least,\nthere is no co-operation of either centre or nerve.--_Proceedings of\nthe Royal Society_, 18th March, 1875. (_See also Studies from the\nPhysiological Laboratory of Cambridge_, Part II., 1876.) Mr. Foster\nknows that I had independently, and from a totally different line\nof research, arrived at the same conclusion respecting the heart\u2019s\nmovement.\n\n[117] _Comptes Rendus de la Soc\u00ed\u00e9t\u00e9 de Biologie_, 1847, I. 40. In\n1856 he showed that not only were the muscles of the iris directly\nstimulated by light (and this not by its calorific or chemical rays),\nbut that sixteen days after removal of the eye from the orbit, this\neffect was observable in the eel. Yet a very few days after extirpation\nof the eye the nerves are disintegrated.--_Proceedings of the Royal\nSociety_, 1856, p. 234.\n\nDONDERS has the following observations: \u201cThe movements of the iris\nare of two kinds--reflex and voluntary. Reflex action is exhibited as\nconstriction of the pupil in consequence of the stimulus of incident\nlight upon the retina. Fontana has shown that the light falling upon\nthe iris produces no remarkable contraction. We have confirmed this\nresult by causing the image of a small distant light to fall, by means\nof a convex lens, upon the iris, whereby, during slight perception of\nlight, a doubtful contraction occurred, which gave way to a strong\ncontraction so soon as the light entering the pupil excited a vivid\nperception. Nevertheless, the experiments of Harless and Budge have\nshown that even after death, so long as irritability remains, the pupil\nstill contracts upon the continued action of light. Of the correctness\nof this we have satisfied ourselves. In a dog killed by loss of blood\nthe one eye was closed, the other opened and turned to the light: after\nthe lapse of an hour, the pupil of the opened eye was perceptibly\nsmaller than that of the closed eye. The latter now remained also\nexposed to the light, and on the following day the diameter of both\neyes was equal. The upper jaw, alone with the eyes, was taken out of\nsome frogs; one eye was exposed to the light, while the other was\ncovered with a closely folded piece of black paper: after the lapse of\nhalf an hour the pupil turned to the light was narrow, the other wide.\nBut the latter also contracted almost immediately after the removal of\nthe paper.\u201d--DONDERS, _On the Anomalies of Accommodation and Refraction\nof the Eye_. Trans. of the New Sydenham Society, p. 572.\n\n[118] The experiment often fails, but I have seen it several times\nsucceed.\n\n[119] _Pfl\u00fcger\u2019s Archiv_, 1872, p. 618.\n\n[120] See his Researches in _Pfl\u00fcger\u2019s Archiv, Bde._ II. and IV.\n\n[121] D\u2019ORBIGNY, _Des Mollusques V\u00edvants et fossils_, p. 113.\n\n[122] _Seaside Studies_, 2d ed., p. 101.\n\n[123] Cited by BROWN S\u00c9QUARD, _Journal de la Physiologie_, 1858, p. 359.\n\n[124] Dr. NORRIS has recorded some striking observations in his paper\non \u201cMuscular Irritability\u201d in the _Journal of Anatomy_, 1867, No. II.\np. 217. Here is the only one I can find room for: \u201cOn taking up the\n_dead_ frog and touching the limb (which during life had been paralysed\nby section of its nerve) with my finger, _it was suddenly shot out\nas if alive_. I placed the body down, and one or two _apparently\nspontaneous movements_ of small extent afterwards occurred. On touching\nthe skin gently with the point of a needle, by the slight pressure upon\nthe muscle beneath, movements of the limb were also induced, but this\nhigh degree of exaltation very rapidly disappeared.\u201d\n\n[125] See their papers in the _Archiv f\u00fcr Psychiatrie_, 1875, Bd. V.\nHeft 3.\n\n[126] This latter statement will be justified when I come to expound\nthe Triple Process, which I have named the _Psychological Spectrum_.\n\n[127] FOSTER and BALFOUR, _Elements of Embryology_, 1874, Part I. p.\n52. HIS, _Untersuchungen \u00fcber die erste Anlage des Wirbelthierleibes_,\n1868, p. 197.\n\n[128] They state that the cells of the epiblast are the results\nof direct segmentation, whereas the cells of the other layers are\nformed at a subsequent period, and are only indirectly results of\nsegmentation. But if the observations of KOWALEWSKY are exact, this is\nnot the case with the hypoblast of the Amphioxus, which is from the\nfirst identical with the epiblast.\n\n[129] K\u00d6LLIKER, _Entwicklungsgeschichte des Menschen und der h\u00f6heren\nThiere_, 1861, p. 71.\n\n[130] [According to BALFOUR\u2019S recent observations, a large part of the\nmuscular tissue is derived from the layer of the mesoblast belonging to\nthe hypoblast.]\n\n[131] HIS, _Untersuchungen_, pp. 39, 40.\n\n[132] Quite recently OWSJANNIKOW has pointed out the termination of\nfibres in the phosphorescent cells of the _Lampyris Noctiluca_. See his\npaper in the _M\u00e9moires de l\u2019Acad. de St. Petersbourg_, 1868, XI. 17.\nThese phosphorescent cells are said to be ganglion-cells by PANCERI,\n_Intorno della luce che emana dalle celleule nervose_ (Rendiconto della\nAccad. delle Scienze, April, 1872); and by EIMER, _Archiv f\u00fcr mikros.\nAnatomie_, 1872, p. 653. K\u00d6LLIKER also calls the phosphorescent organ a\nnervous organ. This is not to be interpreted as meaning that neurility\nis phosphorescence, but simply that in some nerve-cells there is\nphosphorescent matter, which is called into activity by stimulus of the\nnerves.\n\n[133] BIDDER und KUPFFER, _Textur des R\u00fcckenmarks_, 1857, p. 108.\n[What is said in the text has been rendered doubtful by the recent\nresearches of Mr. F. BALFOUR, _On the Development of the Spinal Nerves\nin Elasmobranch Fishes_ (_Philos. Trans._, Vol. CLXVI. Part I.), which\nshow that in these fishes the ganglion has its origin in the spinal\ncord.]\n\n[134] Comp. PROBLEM I. \u00a7 130, with the remarks of CHARLES ROBIN,\n_Anatomie et Physiologie Cellulaires_, 1873, p. 20.\n\n[135] KLEINENBERG, _Hydra; Eine Anatomisch-Entwickelungs-Untersuchung_,\n1872, p. 11. EIMER, _Zoologische Studien auf Capri_, 1873, p. 66.\n\nA similar formation is described by Dr. ALLMAN in the _Myriothela_; he\nsays, however, that he has never been able to trace a direct continuity\nof the caudal processes of the cells with muscular fibrils. He believes\nthat the processes make their way to the muscular layer through\nundifferentiated protoplasm.--_Philos. Transactions_, Vol. CLXV. Part\nII. p. 554.\n\nAn intermediate stage between this neuro-muscular tissue and the two\ndifferentiated tissues seems presented in the Nematoid worms which\nhave muscles that send off processes into which the nerves pass.\nGEGENBAUR declares his inability to decide whether these processes are\nmuscles or nerves. B\u00dcTSCHLI thinks the nerve-process blends with the\nmuscle-process.--_Archiv f\u00fcr mikros. Anatomie_, 1873, p. 89.\n\n[136] \u201cThe gray matter of the cord seems undoubtedly to be formed by a\nmetamorphosis of the external cells of the epiblast of the neural tube,\nand is directly continuous with the epithelium; there being no strong\nline of demarcation between them.\u201d--_Op. cit._, p. 185.\n\n[137] ROBIN, _Anat. et Physiol. Cellulaires_, p. 332.\n\n[138] STILLING, _Bau der Nervenprimitiv-Fasern_, 1856, p. 16.\n\n[139] \u201cThere was a time,\u201d says K\u00d6LLIKER, \u201cwhen I confidently believed\nthat an hypothetical explanation of the arrangement of elements in\nthe spinal cord could be grounded on a basis of fact; but the deeper\nmy insight into the minute anatomy, the less my confidence became;\nand now I am persuaded that the time is not yet come to frame such an\nhypothesis.\u201d--_Gewebelehre_, 5te Auf. 1867.\n\n[140] In the Gasteropoda the cells range from 220 \u03bc to 3 \u03bc (\u03bc = 0,001\nmillim\u00e8tre).\n\n[141] HAECKEL, _M\u00fcller\u2019s Archiv_, 1857. LEYDIG, _Vom Bau des\nthierischen K\u00f6rpers_, 1864, I. 84. ROBIN, _Anat. et Physiol.\nCellulaires_, p. 89. Should the observations of HEITZMANN be\nconfirmed, there would be ground for believing that neurine is\nnormally fibrillated. He says that the living protoplasm in the\nAm\u0153ba, white blood-corpuscle, etc., is an excessively fine network,\nwhich condenses into granules at each contraction. (Cited in the\n_Jahresberichte \u00fcber Anat. und Physiol._, 1873, Bd. II.) WALTHER, who\nexamined frozen brains, describes the cells as quite transparent at\nfirst, with very rare granules, but gradually while under observation\nthe granules became more numerous. _Centralblatt_, 1868, p. 459.\nAccording to MAUTHNER, _Beitr\u00e4ge zur Kenntniss der morphologischen\nElemente des Nervensystems_, 1862, p. 41, neurine has three cardinal\nforms--transparent, finely granular, and coarsely granular.\n\n[142] TRINCHESE, _Struttura del sistema nervoso dei Cefalopodi_,\nFlorence, 1868, p. 7.\n\n[143] An eminent friend of mine was one day insisting to me that the\nphysiological postulate made it _impossible_ for a nerve-cell to be\nwithout its ingoing and outgoing fibres; and he was not a little\nastounded when I replied, \u201cCome into my workroom and I will show you a\nthousand.\u201d\n\n[144] EICHHORST in _Virchow\u2019s Archiv_, 1875, LXIV. p. 432.\n\n[145] AUERBACH (_Ueber einen Plexus Myentericus_, 1862) describes\nthe ganglia as filled with apolar cells, among which only a few are\nunipolar. STIEDA (_Centralnervensystem der V\u00f6gel_, 1868) finds both\napolar and unipolar cells in the spinal ganglia of birds. AXMANN (_De\nGangliorum Systematis Structura penitiori_, 1847) says the spinal cells\nare all unipolar. SCHWALBE (_Archiv f\u00fcr mikros. Anat._, 1868) and\nCOURVOISIER (_ibid._, 1869) say the same. So also RANVIER, _Comptes\nRendus_, 1875. K\u00d6LLIKER (_Gewebelehre_) speaks decidedly in favor of\nboth apolar and unipolar cells, but thinks the apolar are embryonic.\nPAGLIANI (_Saggio sullo Stato attuale delle Cognizioni della Fisiologia\nintorno al Sistema nervoso_, 1873), who represents the views of\nMOLESCHOTT, admits the existence of apolar and unipolar cells. The\nauthors just cited are those I happen to have before me during the\nrewriting of this chapter, and the list might easily be extended if\nneedful. AUERBACH, BIDDER, and SCHWEIGGER-SEIDEL describe unipolar\ncells which in some places present the aspect of bipolar cells simply\nbecause two cells lie together, their single poles having opposite\ndirections. I will add that the bipolar cells do not really render the\nphysiological interpretation a whit more easy than the unipolar, for\nthey are simply cells which form enlargements in the course of the\nnerve-fibres.\n\n[146] When Dr. BEALE says \u201cthat it is probable no nerve-cell exists\nwhich has only _one single fibre_ connected with it\u201d (_Bioplasm_, p.\n186), he has no doubt this in his mind; since he would not, I presume,\ndeny that there are cells each with a single _process_.\n\n[147] DEITERS, _Untersuchungen \u00fcber Gehirn und R\u00fcckenmark_, 1865.\n\n[148] _Archiv f\u00fcr mikros. Anat._, 1869, p. 217. Compere also BUTZKE,\n_Archiv f\u00fcr Psychiatrie_, 1872, p. 584.\n\n[149] HENLE, _Nervenlehre_, 1871, p. 58, Fig.\u00a021.\n\n[150] When men of such experience and skill as K\u00d6LLIKER, BIDDER, GOLL,\nand LOCKHART CLARKE declare that they have never seen a cell-process\npass directly into a dark-bordered fibre in the anterior root, what\nare we to say to such figures and descriptions as those given in the\nworks of SCHR\u00d6DER VAN DER KOLK, GRATIOLET, and LUYS? Even did such\narrangements exist, no transverse nor longitudinal section could\ndisplay them, owing to the different planes at which the fibres enter,\nand the length and irregularity of their course.\n\n[151] Long after the text was written, WILLIGK published in _Virchow\u2019s\nArchiv_, 1875, LXIV. p. 163, observations of anastomoses which even\nK\u00d6LLIKER admitted to be undeniable. Yet out of sixty-four preparations,\namid hundreds of cells, he could only reckon seven cases of conjunction.\n\n[152] See the history given in STILLING\u2019S learned work, _Ueber den Bau\nder Nervenprimitiv-Faser_, p. 34; and compare MAX SHULTZE, _De Retin\u00e6\nStructura_, p. 8, and _Bau der Nasenschleimhaut_, p. 66; WALDEYER, in\nthe _Zeitschrift f\u00fcr rat. Med._, 1863; LISTER and TURNER, _Observations\non the Structure of Nerve-Fibres_, in _Quarterly Micros. Journal_,\n1859; RANVIER, in the _Archives de Physiologie_, 1872.\n\n[153] _Virchow\u2019s Archiv_, Bd. LXXII. p. 193.\n\n[154] _Monthly Journal of Micros. Science_, 1874, XI. p. 214.\n\n[155] BABUCHIN, _Centralblatt_, 1868, p. 756.\n\n[156] Even so eminent an authority as W. KRAUSE holds this both with\nregard to the varicose aspect and the double contour: _Handbuch der\nmenschlichen Anatomie_, 1876, I. 367. BUTSCHLI, however, describes the\nnerves in a living Nematode as varicose: _Archiv f\u00fcr Anat._, 1873, p.\n78; and I have somewhere met with an observation of the double contour\nbeing visible in the living animal.\n\n[157] BUTZKE, _Archiv f\u00fcr Psychiatrie_, 1872, p. 594, states that the\ngranular substance has the chemical composition of myeline. If this\nbe so, we may suppose the \u201cfibrils of crystallization\u201d to represent\nthe coagulation of the substance which is in solution amid the myeline\ngranules, and corresponds with the axis cylinder of a fibre. I may\nremark that in almost every good preparation nerve-cells will be found\nin which, while one process is distinctly granular, another is striated\nor even fibrillated.\n\n[158] BOLL, _Die Histiologie und Histiogenese der nerv\u00f6sen\nCentralorgane_, in the _Archiv f\u00fcr Psychiatrie_, 1873, p. 47.\n\n[159] STIEDA, _Studien \u00fcber das Centralnervensystem der V\u00f6gel_, 1868,\np. 65. MAUTHNER, _Op. cit._, p. 4.\n\n[160] TURNER and LISTER, _Op. cit._, p. 8.\n\n[161] BLESSIG, _De Retin\u00e6 Structura_, 1857.\n\n[162] LUYS, _Recherches sur le Syst\u00e8me nerveux_, 1865, p. 267. In a\nrecent and remarkable treatise the student is informed that \u201cplus\nune cellule est charg\u00e9e d\u2019un r\u00f4le purement m\u00e9canique plus elle est\nvolumineuse; plus l\u2019acte qu\u2019elle produit tend \u00e0 rev\u00eatir un caract\u00e8re\npsychique plus elle est petite\u201d; to move a limb the _agitation_ of\nthe cerebral cells must _materialize itself_ more and more, \u201cIl a\nbesoin de passer par des cellules, de moins en moins spirituelles et\nde plus en plus mat\u00e9rielles.... De m\u00eame pour les cellules sensitives.\nL\u2019impression ext\u00e9rieure va en se modifiant, en se spiritualisant, de la\np\u00e9riph\u00e9rie au centre.... Un ph\u00e9nom\u00e8ne de l\u2019ordre spirituel ne sanrait\ndevenir sans transition un ph\u00e9nom\u00e8ne d\u2019ordre physique.\u201d And what is\nthis marvellous transition between spiritual and physical? It is the\naction of medium-sized cells which \u201ctravaillent la vibration re\u00e7ue, la\nmodifient de fa\u00e7on \u00e0 lui \u00f4ter de son spiritualisme et \u00e0 la rapprocher\ndavantage des \u00e9branlements physiques.\u201d I will not name the estimable\nauthor, because he is simply restating what many others implicitly or\nexplicitly teach; but I will only ask the reader to try and realize in\nthought the process thus described.\n\n[163] SCHR\u00d6DER VAN DER KOLK, _Pathologie der Geisteskrankheiten_, 1863,\np. 69.\n\n[164] WUNDT, _Physiologische Psychologie_, p. 261. In his _Mechanik\nder Nerven, 2 Abth._ (published just as this sheet is going to press),\nhe shows that a stimulus is both retarded and weakened in its passage\nthrough a ganglion.\n\n[165] TRINCHESE also says that the fibres \u201cprovengono dalle cellule e\n_non son altro che i loro prolungamenti o poli_.\u201d--_Op. cit._, p. 13.\nAn unequivocal example is seen in the _Torpedo_, where the large cells\nhave each their prolongation continuing without interruption into the\nelectrical organ. See the figure given by REICHENHEIM in the _Archiv\nf\u00fcr Anat._, 1873, Heft VI.\n\n[166] GOLGI, _Sulla struttura della sostanza grizia del Cervello_.\nARNDT, _Archiv f\u00fcr mikros. Anat._ 1870, p. 176. RINDFLEISCH also traces\nthese processes into the neuroglia (_ibid._, 1872, p. 453). \u201cDeiters,\nBoddaert, and other observers have stated that one dark-bordered\nnerve-fibre enters each cell.... My own observations lead me to\nconclude that _all_ the fibres are composed of the same material, but\nthat one fibre does not divide until it has passed some distance from\nthe cell, while others give off branches much closer to it.\u201d--BEALE,\n_Bioplasm_, p. 189.\n\n[167] BEALE, _Bioplasm_, p. 177. MAX SCHULTZE, in _Stricker\u2019s\nHandbuch_, p. 134. Comp. STILLING, _Nervenprimitiv-Faser_, p. 133.\nARNDT, _Archiv_ _f\u00fcr mikros. Anat._, 1868, p. 512; and 1869, p. 237.\nWeighty as these authorities are, their view is questionable--firstly,\nbecause the forms of these cells are too constant and definite in\nparticular places to result from the union of fibrils coming from\nvarious origins; but secondly, and mainly, because the teaching of\nDevelopment is opposed to it.\n\n[168] ROBIN, _Anat. et Physiol. Cellulaires_, p. 335.\n\n[169] _Archives de Physiologie_, 1872, p. 268.\n\n[170] The fact of the existence of cells in the white substance is one\nwhich is very difficult of interpretation on the current hypotheses.\nThe cells are found in regular columns and irregularly scattered.\nBOLL thinks that while in the white substance of both cerebrum and\ncerebellum there are true nerve-cells as well as connective corpuscles,\nin the cord there are only the latter. But hitherto there has been\nno decisive test by which a nerve-cell can be distinguished from a\nconnective corpuscle.\n\n[171] _Monthly Journal of Micros. Science_, XI. 219. This accords\nwith what KUPFFER says respecting the entire absence of cells\nin the earliest stages observed by him in the sheep. The white\nsubstance of the spinal cord he describes as soft, transparent, and\ngelatinous, in which dark points are visible; these dark points are\nseen in longitudinal sections to arise from the fibrillation of the\nsubstance.--BIDDER und KUPFFER, _Op. cit._, p. 111.\n\n[172] WEISMANN, _Die nachembryonale Entwick. der Musciden_, in the\n_Zeitschrift f\u00fcr Wissen. Zoologie_, 1864, Bd. XIV. Heft III.\n\n[173] The suggestion in the text has since received a striking\nconfirmation in the observations of SIGMUND MAYER on the regeneration\nof nerves. The nerve when divided rapidly undergoes fatty degeneration,\nwhich is succeeded by a transformation of the myeline and axis cylinder\ninto a homogeneous mass; in this resolved pulp new longitudinal\nlines of division appear, which subsequently become new fibres,\nand new nuclei are developed in the remains of the untransformed\nsubstance.--_Archiv f\u00fcr Psychiatrie_, Bd. VI. Heft II.\n\n[174] Strong confirmation of various statements in the text, since\nthey were written, has been furnished by the researches of EICHHORST,\npublished in _Virchow\u2019s Archiv_, LXIV. Our knowledge of the development\nof nerve-tissue in human embryos is so scanty that these researches\nhave a great value. EICHHORST describes the striation of the cells in\nthe cord to begin only at the fourth month; up to this time they are,\nwhat I find most invertebrate cells to be, granular, not fibrillar.\nThere is very slight branching of the cell processes until the ninth or\ntenth month, when the multipolar aspect first appears; the cells are\nunipolar up to the end of the fourth month. The connection between the\nwhite columns and the gray columns is very loose up to the fifth month;\nand the two are easily separated. Subsequently the union is closer.\nThe substance of the white columns readily separates into bundles and\nfibres, but that of the gray columns falls into a granular detritus if\nattempted to be teased out with needles. But after the fifth month this\nis no longer so. Instead of a granular detritus there appears a network\nof fine fibres and fibrils. Although the white posterior columns are\ndeveloped before the fifth month, not a single cell can be seen in\nthe posterior gray columns until the second half of the ninth month.\n(Yet the fibres are imagined to arise in the cells!) The passage from\nthe granular to the fibrillar state is the same in the cell substance\nand the neuroglia. The nerve-fibre, as distinguished from a naked\naxis cylinder, does not appear till the fourth month. It is at first\na bipolar prolongation of the nucleus. As it elongates, the nucleus\nseems to sit _on_ it, and so loosely that it is easily shifted away by\npressure on the covering glass. Finally the fibre separates entirely\nfrom the nucleus, and _then_ begins to clothe itself with the medullary\nsheath. Very curious is the observation that so long as the axis\ncylinder is naked it is never varicose, but with the development of the\nmedulla the primitive axis becomes fluid.\n\n[175] MAYER, _Op. cit._, 393. I cannot, however, agree with MAYER when\nhe says that the continuity of a nerve-fibre with a cell has _never_\nbeen distinctly shown (p. 395); in the Invertebrata and in the Electric\nfishes such a continuity is undeniable; and it has occasionally been\nseen in Vertebrata.\n\n[176] RANVIER, in the _Comptes Rendus_, 1875, Vol. LXXXI. p. 1276. This\nobservation throws light on the fact that cell processes are sometimes\nseen entering nerve-roots (\u00a7 124).\n\nThe very remarkable observations of Mr. F. BALFOUR, _On the Development\nof the Spinal Nerves in Elasmobranch Fishes_ (_Philos. Trans._, Vol.\nCLXVI. p. 1), show that the spinal root, ganglion, and nerve-trunk\narise from histological changes in a mass of cells at first all alike;\n_not_ that ganglion-cells are formed and from their processes elongate\ninto fibres. The nerve, he says, forms a continuation of its root\nrather than of its ganglion (p. 181); which accords with RANVIER\u2019S view.\n\n[177] In the _Handbuch der menschlichen Anatomie_ of W. KRAUSE, which\nhas just appeared, I am pleased to find a similar view, p. 376.\n\n[178] On this point consult AXEL KEY and RETZIUS, in the _Archiv f\u00fcr\nmikros. Anat._, 1873, p. 308, where the nutritive disturbance is\nassigned to the fact that the lymph can no longer take its normal\ncourse. WALLER\u2019S observations on the degeneration of the optic nerves,\nwith preservation of the integrity of the retina, after division of the\nnerves (_Proceedings of Royal Society_, 1856, p. 10), cannot be urged\nin support of his view, because BERLIN and LEBERT\u2019S observations are\ndirectly contradictory of his. SAEMISCH _und_ GRAEFE, _Handbuch der\nAugenheilkunde_, II. 346. It is said by KRENCHEL that if the nerves\nbe divided, so as to prevent disturbances in the circulation, no\nperipheral degeneration takes place (cited by ENGELMANN in _Pfl\u00fcger\u2019s\nArchiv_, 1875, p. 477).\n\n[179] SCHIFF, _Lehrbuch der Physiologie_, pp. 120, 121.\n\n[180] K\u00d6LLIKER, _Gewebelehre_, 317. SCHWALBE, _Archiv f\u00fcr mikros.\nAnat._, 1868, p. 51.\n\n[181] I was first shown this in 1858 by the late Prof. HARLESS in\nMunich, who at the same time showed me that the nerve thus bared of\nits sheath, if left some hours in gastric juice, split up into regular\ndiscs, like the sarcous elements of muscles.\n\n[182] STIEDA, _Bau des centralen Nervensystem der Amphibien und\nReptilien_, 1875, p. 41.\n\n[183] BUTZKE, in _Archiv f\u00fcr mikroskopische Anatomie_, Bd. III. Heft 3,\np. 596.\n\n[184] Except in the rare cases where there is anastomosis of the\nmuscle-fibres; as, for example, in the heart. [According to ENGELMANN\u2019S\nremarkable researches, the muscles of the heart form a continuum,\nso that irritation is propagated from one to the other: _Pfl\u00fcger\u2019s\nArchiv_, 1875, p. 465. This is indubitably the case in the embryonic\nheart, as ECKHARD pointed out.] This I hold to be the main cause of\nits rhythmic pulsation after removal from the body. Whatever influence\nthe ganglia may have in exciting this pulsation, such influence would\nbe powerless were not the muscles so connected; as may be seen in the\nother organs which are richly supplied with ganglia, yet do not move\nspontaneously; and in organs (such as the ureter or the embryonic\nheart, and the hearts of invertebrata) which move spontaneously, yet\nhave no ganglia.\n\n[185] SCHR\u00d6DER VAN DER KOLK, _Bau und Funktionen der Med. Spinalis_, p.\n67.\n\n[186] It is very instructive to learn that for some six months or so\nthe rat is quite incapable of correctly _localizing_ the pain.\n\n[187] VULPIAN, _Le\u00e7ons sur le Syst\u00e8me Nerveux_, p. 288. The experiment\nhas been confirmed by ROSENTHAL, and by BIDDER (_Archiv f\u00fcr Anatomie_,\n1865, p. 246), who first (in 1842) attempted this union of different\nnerves, but arrived at negative results; as did SCHIFF (_Lehrbuch\nder Physiol_, 1859, p. 134) and GLUGE _et_ THIERNESSE (_Annales des\nSciences Naturelles_, 1859, p. 181).\n\n[188] SACHS, in the _Archiv f\u00fcr Anat._, 1874, pp. 195, _sq._\n\n[189] LAPLACE, _Essai Philos. sur les Probabilit\u00e9s_, p. 239.\n\n[190] The mode of termination of nerves in muscles is still a point\non which histologists disagree; probably because there is no abrupt\ntermination, but a blending of the one tissue with the other. In the\nTardigrades, for example, there is actually no appreciable distinction\nbetween nerve and muscle at the point of insertion of the nerve; and\nif in the higher animals there is an appreciable difference between\nnerve and muscle, there is an inseparable blending of undifferentiated\nsubstance at their point of junction. [According to ENGELMANN\u2019S\nrecent researches, there seems good reason to suppose that muscles\nare composed of contractile substance and a substance which is a\nmodification of axis-cylinder substance; the first being doubly\nrefracting, the second isotropic: _Pfl\u00fcger\u2019s Archiv_, 1875, p. 432.]\n\n[191] SCHIFF, _Lehrbuch_, p. 73.\n\n[192] FREUSBERG observed that the reflex movements in the legs of a\ndog whose spine had been divided were considerably lessened after\nfood or drink. They fell from 95 to 46 pendulum-beats in a minute\nafter a _litre_ of water had been drunk. See his instructive memoir,\n_Reflex-L\u00e4hmungen beim Hunde_, in _Pfl\u00fcger\u2019s Archiv_, 1874, p. 369.\n\n[193] M. HERZEN thus describes the effects of stimulating the vagus\nwith varying intensities: \u201cSi l\u2019on se sert de l\u2019appareil de Dubois\nRaymond, on commence par appliquer une irritation tellement faible\nqu\u2019elle ne produit aucun effet; on rapproche alors peu \u00e0 peu lea\ndeux bobines de l\u2019appareil avec le plus grand soin, par fractions de\ncentim\u00e8tres, par _millim\u00e8tres_ s\u2019il le faut, et l\u2019on trouve ainsi\nle degr\u00e9 d\u2019irritation qui accel\u00e8re les battements du c\u0153ur et qui\nproduit le maximum de pulsations dans l\u2019unit\u00e9 de temps admise pour\nl\u2019exp\u00e9rience. Quand on est l\u00e0 il suffit _d\u2019un millim\u00e8tre_ de plus pour\nfaire dispara\u00eetre l\u2019augmentation, un autre millim\u00e8tre peut produire une\ndiminution, et un _troisi\u00e8me_ peut arr\u00eater le c\u0153ur compl\u00e8tement. En\nreculant alors, en \u00e9loignant peu \u00e0 peu les deux bobines, _on r\u00e8tourne\n\u00e0 la force qui produit l\u2019augmentation des battements_.\u201d HERZEN,\n_Exp\u00e9riences sur les Centres Mod\u00e9rateurs de l\u2019Action R\u00e9flexe_, 1864,\np. 68. There have been serious doubts thrown on these experiments; but\nseveral experimenters have confirmed their exactness. Quite recently\nthey have been confirmed by BULGHERI, _Il Morgagni_, VIII.; and by\nARLOING and TRIPIER, _Archives de Physiologie_, 1872, IV. p. 418. It\nmust be confessed, however, that the whole subject of the heart\u2019s\ninnervation is at present very imperfectly understood.\n\n[194] CAYRADE, _Recherches sur les Mouvements R\u00e9flexes_, 1864, p. 58.\n\n[195] A frog\u2019s brain is removed, and the body then suspended by the\nlower jaw, the legs are allowed to dip into a slightly acidulated\nliquid, the chemical action of which stimulates the skin.\n\n[196] I saw a patient in the Berlin _Charit\u00e9_ whose face and left hand\nwere in a constant state of convulsive twitching, but no sooner was a\nscar on the left hand (where the nerve had been divided) firmly pressed\nthan the twitchings ceased, and _pain_ was felt; on removal of the\npressure, pain ceased and the twitchings returned.\n\n[197] _Pfl\u00fcger\u2019s Archiv_, 1875. No one interested in the Reflex Theory\nshould omit a careful study of the papers by FREUSBERG and GOLTZ. I\nhave drawn freely from them.\n\n[198] Sir JAMES PAGET has an interesting collection of facts which\nillustrate this Law of Arrest, in his paper on \u201cStammering with other\nOrgans than those of Speech,\u201d _British Medical Journal_, 1868, Vol. II.\np. 437, reprinted in his _Clinical Lectures and Essays_, 1875, p. 77.\n\n[199] _Archives de Physiol._, 1868, p. 157.\n\n[200] _West Riding Lunatic Asylum Reports_, 1874, p. 200.\n\n[201] CLAUDE BERNARD, _Syst\u00e8me Nerveux_, I. 383.\n\n[202] See the excellent remarks of Dr. LAUDER BRUNTON on this point in\nhis paper on Inhibition in the _West Riding Lunatic Asylum Reports_,\n1874, p. 180.\n\n[203] The interesting question of interference has been experimentally\ntreated by WUNDT in his recently published _Mechanik der Nerven_, 1876,\nand theoretically as wave-movement by MEDEM, _Grundz\u00fcge einer exakten\nPsychologie_, 1876.\n\n[204] On the distinction between first notions and theoretic\nconceptions, see _Problems of Life and Mind_, Vol. II. p. 277.\n\n[205] Not transcendental and _a priori_, as Kant teaches; but immanent\nin Feeling.\n\n[206] The reader will understand that although mechanical relations\nare modes of Feeling, as all other relations are, yet their aspect\nis exclusively objective, referring to objects ideally detached from\nsubjects.\n\n[207] ANTOINE CROS, _Les Fonctions sup\u00e9rieures du Syst\u00e8me nerveux_,\n1875, p. 85.\n\n[208] The solution offered in the present chapter was first offered\nin _Problems of Life and Mind_, 1875, II. 465, _sq._ I mention\nthis because since the publication of that volume other writers\nhave expressed the same ideas, sometimes using my language and\nillustrations: e.\u00a0g. M. TAINE in the _Revue Philosophique_, January,\n1877, art., _Les Vibrations c\u00e9r\u00e9brales et la Pens\u00e9e_.\n\n[209] _Problems of Life and Mind_, Vol. II. pp. 443 and 482.\n\n[210] \u201cThe retinal image is the last effect known of the action\nof objects on us; what happens beyond the retina we know not;\nour knowledge of the objective process has at present here its\nlimit.\u201d--EWALD HERING, _Beitr\u00e4ge zur Physiologie_, 1862, p. 166. That\nis to say, we have a definite translation of the process in geometric\nterms as far as the retina, and thence onwards Geometry fails us, and\nNeurology and Psychology are invoked.\n\n[211] Compare PROBLEM II. Chap. IV.\n\n[212] \u201cDas Bewusstwerden ist nichts Anderes als ein weiter\nfortgeschrittenes Erinnern oder Neuwerden des von aussen aufgenommenen\nWissens, ein innerliches Wissen dieses Wissens oder ein in sich\nreflectirtes Wissen.\u201d--JESSEN, _Versuch einer Wissenschaftlichen\nBegr\u00fcndung der Psychologie_, 1855, p. 477.\n\n[213] In common language a stone or a tree is said to be unconscious;\nbut this is an anthropomorphic extension of the term. In strictness we\nshould no more speak of unconsciousness outside the sphere of Sentience\nthan of darkness outside the sphere of Vision.\n\n[214] The contraction may be effected in the eye out of the organism.\nSee p. 229. It is then no reflex.\n\n[215] _Glasgow Medical Journal_, 1857, p. 451. See also further on,\nnote to p. 426.\n\n[216] MAYER, _Die Elementarorganisation des Seelenorgans_, p. 12, is\nthe authority for the last statement.\n\n[217] _Allgemeine Zeitschrift f\u00fcr Psychiatrie_, Bd. 31, p. 711.\n\n[218] AUBERT, _Grundr\u00fcge der physiol. Optik_, 1876, p. 633. \u201cThe\naccommodative movement of the eye is to be considered voluntary. It is\ntrue we contract the pupil without being conscious of the contraction\nof muscular fibres, _but this holds good for every voluntary movement_.\nWhen a person raises the tone of his voice he is not conscious that\nby muscular contraction he makes his chord\u00e6 vocales more tense; he\nattains his object without being aware of the means by which he does\nso. The same is applicable to accommodation for near objects and to\nthe contraction of the pupil accompanying it. The fact that _this last\nis only an associated movement does not deprive it of its voluntary\ncharacter_, for there is perhaps no single muscle which can contract\nentirely by itself.\u201d DONDERS, _On the Anomalies of Accommodation_,\n1864, p. 574. Professor BEER of Bonn has the rare power of contracting\nor dilating the pupils of his eye at will; here ideas act as motors.\nWhen he thinks of a very dark space the pupil dilates, when of a very\nbright spot the pupil contracts. (NOBLE, _The Human Mind_, 1858, p.\n124.) I believe this to be only an exaggerated form of the normal\ntendency. In all of us the mechanism is so disposed that the feelings\nof dilatation are associated with feelings (and consequently ideas) of\ndarkness; and by this association a reversal of the process obtains, so\nthat the idea of darkness calls up the feeling it symbolizes.\n\n[219] SPENCER, _Principles of Psychology_, I. 499.\n\n[220] DESCARTES expressly calls them sensitive machines. He refuses\nthem Thought, but neither \u201cla vie ou le sentiment.\u201d He adds, \u201cMon\nopinion n\u2019est pas que les b\u00eates voient comme nous lorsque nous sentons\nque nous voyons.\u201d--_\u0152uvres_, IV. p. 339. This example is cited by him\nin proof of human automatism: \u201cQue ce n\u2019est point par l\u2019entremise de\nnotre \u00e2me que les yeux se ferment, puisque c\u2019est contre notre volont\u00e9,\nlaquelle est sa seule ou du moins sa principale action; mais c\u2019est\n\u00e0 cause que la machine de notre corps est tellement compos\u00e9e que le\nmouvement de cette main vers nos yeux excite un autre mouvement en\nnotre cerveau qui conduit les esprits animaux dans les muscles qui font\nabaisser les paupi\u00e8res.\u201d All indeed that we assign to Sensibility, he\nassigns to these hypothetical animal spirits, and thence he concludes,\n\u201cQu\u2019il ne reste rien en nous que nous devions attribuer \u00e0 notre \u00e2me\nsinon nos pens\u00e9es.\u201d--_Les Passions de l\u2019\u00c2me_, art. 13 and 17. Comp.\n_Discours de la M\u00e9thode_, partie iv.\n\n[221] DESCARTES compares the animal mechanism to that of the grottos\nand fountains at Versailles, the nerves to the water-tubes:--\u201cLes\nobjets ext\u00e9rieurs qui par leur seul pr\u00e9sence, agissent contre les\norganes des sens, et qui par ce moyen, la d\u00e9terminent \u00e0 se mouvoir\nen plusieurs diverses fa\u00e7ons, selon comme les parties du cerveau\nsont dispos\u00e9es, sont comme les \u00e9trangers, qui entrant dans quelques\nunes des grottes de ces fontaines causent euxm\u00eames sans y penser les\nmouvements qui s\u2019y font en leur pr\u00e9sence: car ils n\u2019y peuvent entrer\nqu\u2019en marchant sur certains carreaux tellement dispos\u00e9s, que s\u2019ils\napprochent d\u2019une Diane qui se baigne, ils la font cacher dans les\nroseaux; et s\u2019ils passent outre pour la poursuivre, ils feront venir\nvers eux un Neptune qui les menacera de son trident; ou s\u2019ils vont de\nquelque autre cost\u00e9, ils en feront sortir un monstre marin qui leur\nvomira de l\u2019eau contre la face.\u201d--_Trait\u00e9 de l\u2019Homme_, 1664, p. 12.\nIngenious as the comparison is, it only illustrates how machines may\nbe constructed to imitate animal actions. Diana always hides herself\nwhen a certain spot is trodden upon; and Neptune always appears when\nanother spot is trodden upon. There is no fluctuation, no sensibility\ndiscerning differences and determining variations. Compare the\nfollowing experiment: A monkey was placed on the table and a shrill\nwhistle made close to its ear: \u201cImmediately the ear was pricked and\nthe animal turned with an air of intense surprise, with eyes widely\nopened and pupils dilated, to the direction whence the sound proceeded.\nOn repetition of the experiment several times, though the pricking\nof the ear and the turning of the head and eyes constantly occurred,\nthe look of surprise and dilatation of the pupils ceased to be\nmanifested.\u201d--FERRIER, _The Functions of the Brain_, 1876, p. 171. A\nmechanical monkey would always have reacted in precisely the same way\non each stimulus.\n\n[222] Printed in the _Fortnightly Review_, November, 1874, from which\nall my citations are made.\n\n[223] SCHIFF, _Lehrbuch der Physiol._, 1858, p. 212. HERMANN,\n_Physiology_, translated by GAMGEE, 1875, p. 511.\n\n[224] Meanwhile the reader is referred to SCHR\u00d6DER VAN DER KOLK,\n_Pathologie der Geisteskrankheiten_, 1863, p. 51; or JESSEN,\n_Physiologie des menschlichen Denkens_, 1872, p. 66.\n\n[225] GRIESINGER, _Les Maladies Mentales_, p. 96.\n\n[226] M. LUYS cites the case of a patient who conversed quite\nrationally with a visitor \u201csans en avoir conscience, et ne se\nsouvenait de rien\u201d; and he draws the extraordinary conclusion that\nthe conversation \u201cs\u2019op\u00e9rait en vertu des forces r\u00e9flexes.\u201d--_\u00c9tudes\nde Physiologie et de Pathologie C\u00e9r\u00e9brales_, 1874, p. 117. Is it\nnot obvious that the patient must have been conscious at the time,\nthough the consciousness vanished like that in a dream? The persistent\nconsciousness is the continuous linking on of one state with previous\nstates--the apperception of the past.\n\n[227] ABERCROMBIE, _Inquiries concerning the Intellectual Powers_,\n1840, p. 151. WIGAN, _The Duality of the Mind_, 1844, p. 270. DESPINE,\n_La Psychologie Naturelle_, 1868, I. 54.\n\n[228] Dr. HUGHLINGS JACKSON has quite recently cited some curious\nexamples in his own practice. See _West Riding Lunatic Asylum Reports\nfor 1875_.\n\n[229] PROBLEMS, Vol. II. p. 478, _sq._\n\n[230] \u201cLe sentiment fait na\u00eetre le mouvement, et le mouvement donne\nnaissance au sentiment.\u201d--VAN DEEN, _Trait\u00e9s et D\u00e9couvertes sur la\nMo\u00eblle \u00c9pini\u00e8re_, 1841, p. 102.\n\n[231] Dr. CARPENTER tells a similar story of Admiral CODRINGTON, who,\nwhen a midshipman, could always be awakened from the profoundest\nslumber if the word \u201csignal\u201d were uttered; whereas no other word\ndisturbed him.\n\n[232] Compare an interesting personal example given by JOUFFROY, quoted\nin Sir W. HAMILTON\u2019S _Lectures_, I. 331.\n\n[233] _Lancet_, 10th July, 1858.\n\n[234] MARSHALL HALL in _Philos. Trans._, 1833. _Lectures on the Nervous\nSystem and its Diseases_, 1836. _New Memoir on the Nervous System_,\n1843.\n\n[235] M\u00dcLLER, _Physiology_, I. 721.\n\n[236] It is better simply to remove the brain, than to remove the whole\nhead, which causes a serious loss of blood. An etherized animal may be\noperated on with ease and accuracy. For many experiments, mere division\nof the spinal cord is better than decapitation. Great variations in the\nresults must be expected, because the condition of the animal, its age\nand sex--whether fasting or digesting--whether the season be spring or\nsummer--and a hundred other causes, complicate the experiment.\n\n[237] VOLKMANN, quoted by PFL\u00dcGER.\n\n[238] UNZER, _The Principles of Physiology_ (translated for the\nSydenham Society), p. 235.\n\n[239] Even so eminent an investigator as GOLTZ has fallen into this\nconfusion. He introduces an experiment to prove that the brainless\nfrog is insensible to pain by the words \u201cwhen an animal, placed under\ncircumstances which would be very painful, makes no movement, although\nquite capable of moving, the least we can say is that it is improbable\nthat the animal has sensation\u201d (_Nervencentren des Frosches_, p.\n127). I need not discuss the proof itself, having already done so in\n_Nature_, Vol. IX. p. 84. The point to which I wish to call attention\nis the confusion of insensibility in general with insensibility to pain.\n\n[240] See DUCHENNE, _De \u00c9lectrisation localis\u00e9e_, p. 398. GRIESINGER\ncites various examples of insane patients who have burned the flesh off\ntheir bones while manifesting a total indifference to these injuries.\n_Maladies Mentales_, p. 94. FALRET says, \u201cNous avons vu plusieurs\nfois des ali\u00e9n\u00e9s s\u2019inciser, s\u2019amputer eux-m\u00eames diverses parties du\ncorps sans para\u00eetre ressentir aucune souffrance.\u201d _Le\u00e7ons cliniques\nde M\u00e9dicine Mentale_, 1854, I. 189. Patients incapable of feeling the\ncontact of a hot iron with their skin have felt subjective burnings in\nthe skin thus objectively insensible.\n\n[241] CROS, _Les Fonctions sup\u00e9rieures du Syst. nerveux_, 1875, p. 27.\n\n[242] _Virchow\u2019s Archiv_, Bd. XXVIII. p. 30.\n\n[243] The idea of a _fixed anatomical mechanism_ for reflexion, such\nas that of an excito-motory system, is completely refuted by the fact\nthat the gray substance may anywhere be cut sway, and yet so long\nas a small bridge of gray substance remains the stimulation will be\npropagated through it. The idea of a _fixed pathway_ is also refuted by\nthe fact of the variations in the reflex responses, and the necessary\nirradiation even for very simple reflexes. Take, for example, that of\nbreathing. An irritation of the bronchial filaments is transmitted by\nthe pneumogastric to its centre in the medulla oblongata; from this,\nhowever, it is immediately irradiated _downwards_ to the cervical and\ndorsal regions, which innervate the muscles of chest and diaphragm, and\n_upwards_ to the brain, whether the stimulation awaken consciousness or\nnot. One may say, indeed, that inasmuch as under normal conditions the\nbronchial irritation always causes a movement of a particular group of\nmuscles, there is to this extent a fixed pathway of discharge; but, as\nI have formerly explained, this is only an expression of the particular\ntension of particular centres, and is variable with that tension; the\nother centres are also affected, even when they are not excited to\ndischarge.\n\n[244] LALLEMAND, _Recherches sur L\u2019Enc\u00e9phale_, III. 310.\n\n[245] _West Riding Lunatic Asylum Reports_, 1875, Vol. V. pp. 252, _sq._\n\n[246] GALL _et_ SPURZHEIM, _Anat. et Physiol. du Syst\u00e8me Nerveux_, I.\n83.\n\n[247] Printed in the _British and Foreign Medical Review_, Jan. 1845.\n\n[248] GRIESINGER, _Abhandlungen_, 1872. The first volume contains a\nreprint of this memoir.\n\n[249] LANDRY, _Trait\u00e9 des Paralysies_, I. 55. Conf. ZIEMSSEN, _Chorea_\nin the _Handbuch der speciellen Pathologie_, Bd. XII. 2, p. 408. And\nLUYS, _\u00c9tudes de physiol. et pathol. c\u00e9r\u00e9brales_, 1874, pp. 89\u201394.\n\n[250] SUE, _Recherches Philosophiques sur la Vitalit\u00e9 et le\nGalvanisme_, p. 9. He was not consistent, however, but adopted Bichat\u2019s\nopinion respecting the sensibility of the viscera, p. 68.\n\n[251] LEGALLOIS, _Exp\u00e9riences sur le principe de la vie_. Published,\nI conclude, in 1811; the edition I use is the one printed in the\n_Encyclop\u00e9die des Sciences Medicales_, IV.\n\n[252] WILSON PHILIP, _Experimental Inquiry into the Laws of the Vital\nFunctions_, pp. 209, 210.\n\n[253] LONGET, _Trait\u00e9 de Physiologie_, II. 105.\n\n[254] He cites Cuvier, Majendie, Deamoulins, and Mayo as maintaining\nthis error.\n\n[255] GRAINGER, _Structure and Functions of the Spinal Cord_, p. 66.\n\n[256] NASSE, _Unters. zur Physiologie und Pathologie_, Vol. II. Part 2.\n\n[257] CARUS, _System der Physiologie_, III. 101.\n\n[258] J. W. ARNOLD, _Die Lehre von der Reflex-Function_, 86.\n\n[259] PFL\u00dcGER, _Die sensorischen Functionen des R\u00fcckenmarks der\nWirbelthiere_.\n\n[260] Except AUERBACH, who repeated and varied the experiments; and\nFUNKE, who partially adopted the conclusions in his systematic treatise\non Physiology.\n\n[261] SCHIFF, _Lehrbuch der Physiologie_, 208.\n\n[262] LANDRY, _Trait\u00e9 des Paralysies_, 1859, maintains that the cord is\na centre of sensation, and that there is in it a faculty _analogous_\nto the perception and judgment of the brain. Compare pp. 163 _et sq._\nand 305. He also cites an essay by Dr. PATON of Edinburgh (_Edinburgh\nMedical Journal_, 1846), in which the sensational and volitional claims\nof the spinal cord are advanced.\n\n[263] GOLTZ, _Beitr\u00e4ge zur Lehre von den Functionen der Nervencentren\ndes Froeches_, 1869.\n\n[264] _Pfl\u00fcger\u2019s Archiv_, Bd. XIV. p. 158.\n\n[265] See Prob. II. \u00a7 183.\n\n[266] \u201cIl y a donc une m\u00e9moire par le cerveau et une m\u00e9moire par\nl\u2019automate. Tous les organes ont une m\u00e9moire propre, c\u2019est \u00e0 dire _une\ntendance \u00e0_ reproduire les s\u00e9ries d\u2019actes qu\u2019ils ont plusieurs fois\nexecut\u00e9s.\u201d--GRATIOLET, _Anat. du Syst\u00e8me Nerveux_, 1857, p. 464.\n\n[267] To obviate misunderstanding let me say that, unless the contrary\nis specified, I use the term Brain throughout this argument as\nequivalent to the cerebral hemispheres, because it is in these that\nsensation, volition, and consciousness are localized by the generality\nof writers, many of whom, indeed, regard the cells of the gray matter\nof the convolutions as the exclusive seat of these phenomena, dividing\nthese cells into sensational, emotional, and intellectual. There\nare physiologists who extend sensation to the cerebral ganglia and\ngray masses of the medulla oblongata; but the medulla spinalis is so\nclearly continuous with the medulla oblongata that there is a glaring\ninconsistency in excluding sensation from the one if it is accorded to\nthe other; and the grounds on which sensitive phenomena are admitted in\nthe absence of the hemispheres, force us to admit analogous phenomena\nin the absence of the ganglia and medulla oblongata: in each case the\nphenomena are less complex and varied as the mechanisms become less\ncomplex.\n\n[268] Compare LUSSANA e LEMOIGNE, _Fisiologia dei centri encefalici_,\n1871, II. 239, 240, 330.\n\n[269] See a very interesting case of this special loss of memory\nin a priest who still occupied himself reading classic authors and\nperforming his official duties many months after an injury to the\nbrain. LUSSANA e LEMOIGNE, _Fisiologia dei centri encefalici_, I. 201.\n\n[270] BOUILLAUD, _Recherches Exp\u00e9rimentales sur les Fonctions du\nCerveau en g\u00e9n\u00e9ral_, 1830, p. 5, _sq._\n\n[271] LONGET, _Trait\u00e9 de Physiologie_, II. 240.\n\n[272] DALTON, _Human Physiology_, Philadelphia, 1859, p. 362.\n\n[273] DALTON, p. 362.\n\n[274] DALTON, p. 363.\n\n[275] FLOURENS, p. 89.\n\n[276] LEYDEN in the _Berliner klinische Wochenschrift_, 1867, No. 7.\nMEISSNER, _Jahresbericht \u00fcber Physiol._, 1867, p. 410.\n\n[277] VOIT in the _Sitzungsberichte der M\u00fcnchener Academie_, 1868, p.\n105. Comp. also GOLTZ in _Pfl\u00fcger\u2019s Archiv_, Bd. XIV. 435.\n\n[278] VULPIAN, _Syst\u00e8me Nerveux_, 542\u201348.\n\n[279] For other examples see GINTRAC, _Pathologie Interne_, 1868, VI.\n51\u201357.\n\n[280] If the water is perfectly still the fish sinks to the bottom and\nremains motionless until the water be stirred. Mere _contact_ does not\nsuffice; there must be intermittent pulses from the moving water.\n\n[281] LUSSANA e LEMOIGNE, _Op. cit._, I. 15.\n\n[282] _Archives de Physiologie_, 1869, p. 539.\n\n[283] BR\u00dcCKE, _Physiologie_, II. p. 53. While these sheets are passing\nthrough the press, GOLTZ has published his second series of experiments\non the brain. The following detail is a good illustration of what is\nsaid in the text: A dog deprived of a portion of both hemispheres\ndisplayed a marked imperfection in the execution of ordinary instincts.\nAlthough sight was impaired he could see, and recognize men and certain\nobjects: the sight of a whip made him cower, but the sight of meat\ndid not suffice to set the feeding mechanism in action. When meat\nwas suspended above his head, the scent caused him to sniff about in\nsearch, but he failed to find it, and even when he was so placed that\nhe could see the suspended meat, the _unusual_ impression failed to\nguide him. If the meat were held towards him, or placed before him in\na dish, he took it at once--this being the customary stimulation. So\nalso, if the hand were held up, in the usual way when dogs are made\nto leap for food, this dog sprang vigorously up and caught the food;\nbut he would spring up in the same way when the hand was held empty,\nand continue fruitlessly springing, whereas an uninjured dog ceases to\nspring when he sees the hand is empty.--_Pfl\u00fcger\u2019s Archiv_, Bd. XIV. p.\n419.\n\n[284] GRATIOLET, _Anat. Compar\u00e9e du Syst\u00e8me Nerveux_, 1857, p. 459.\n\n[285] LUSSANA e LEMOIGNE, _Op. cit._, I. 363.\n\n[286] _Virchow\u2019s Archiv_, Bd. LX. pp. 130\u201333. Yet there are many\nphysiologists who persist in placing the _motorium commune_ in the\n_corpora strata_! And they place the _sensorium commune_ in the optic\nthalami, although, not to mention the ambiguous evidence of Pathology,\nthe experiments of NOTHENGEL and VEYSSI\u00c8RE show that destruction of\nthe thalami does not destroy sensation. See VEYSSI\u00c8RE, _Recherches\nsur l\u2019h\u00e9mianesth\u00e9sie de cause c\u00e9r\u00e9brale_, 1874, pp. 83, 84. I may\nobserve, in passing, that the notion of the _corpora striata_ being\nthe necessary channel for volitional impulses, and the _optic thalami_\nfor reflex actions, is utterly disproved by the experimental evidence\nrecorded in the text, as well as in \u00a7 66.\n\n[287] _Pfl\u00fcger\u2019s Archiv_, Bde. VIII. and IX.\n\n\n\n\nTranscriber\u2019s Notes\n\n\nPunctuation, hyphenation, and spelling were made consistent when a\npredominant preference was found in the original book; otherwise they\nwere not changed.\n\nSimple typographical errors were corrected; unbalanced quotation\nmarks were remedied when the change was obvious, and otherwise left\nunbalanced.\n\nIllustrations in this eBook have been positioned between paragraphs and\nnearer to the text that references them.\n\nFootnotes in this eBook have been collected and moved to the end of the\nbook.\n\nThe Table of Contents entry for Problem II, Chapter II, referenced the\nwrong page; corrected here.","title":"The Physical Basis of Mind: Being the Second Series of Problems of Life and Mind.","tradition":"philosophy-ethics","translated_text":null,"word_count":169715}