{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_60773/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_60773","id":"gutenberg_60773","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/60773","summary":null,"tags":["Category: Health & Medicine","Category: Philosophy & Ethics","Category: Science - Biology","Hygiene","Physiology"],"text":"TRANSCRIBER'S NOTE: Italic text is denoted by _underscores_ and bold\ntext by =equal signs=.\n\n\n\n\n  THE\n\n  PHILOSOPHY OF HEALTH;\n\n  OR,\n\n  AN EXPOSITION\n\n  OF THE\n\n  PHYSICAL AND MENTAL CONSTITUTION\n  OF MAN,\n\n  WITH A VIEW TO THE PROMOTION OF\n\n  HUMAN LONGEVITY AND HAPPINESS.\n\n  BY\n\n  SOUTHWOOD SMITH, M.D.,\n\n  _Physician to the London Fever Hospital, to the Eastern Dispensary,\n  and to the Jews' Hospital._\n\n  IN TWO VOLUMES. VOL. I.\n\n  _THIRD EDITION._\n\n  LONDON:\n  C. COX, 12, KING WILLIAM STREET, STRAND.\n\n  1847.\n\n\n\n\nLondon: Printed by W. CLOWES and SONS, Stamford Street.\n\n\n\n\nCONTENTS OF VOL. I.\n\n\n    INTRODUCTION                                                Page 1\n\n\n    CHAPTER I.\n\n    Characters by which living beings are distinguished\n    from inorganic bodies\u2014Characters by which\n    animals are distinguished from plants\u2014Actions\n    common to plants and animals\u2014Actions peculiar\n    to animals\u2014Actions included in the ORGANIC\n    circle\u2014Actions included in the ANIMAL\n    circle\u2014Organs and functions defined\u2014Action of\n    physical agents on organized structures\u2014Processes\n    of supply, and processes of waste\u2014Reasons why the\n    structure of the animal is more complex than that\n    of the plant                                                    13\n\n\n    CHAPTER II.\n\n    Two distinct lives combined in the\n    animal\u2014Characters of the apparatus of the organic\n    life\u2014Characters of the apparatus of the animal\n    life\u2014Characteristic differences in the action of\n    each\u2014Progress of life\u2014Progress of death                       51\n\n\n    CHAPTER III.\n\n    Ultimate object of organization and life\u2014Sources\n    of pleasure\u2014Special provision by which the\n    organic organs influence consciousness and afford\n    pleasure\u2014Point at which the organic organs cease\n    to affect consciousness and why\u2014The animal\n    appetites: the senses: the intellectual faculties:\n    the selfish and sympathetic affections: the moral\n    faculty\u2014Pleasure the direct, the ordinary,\n    and the gratuitous result of the action of the\n    organs\u2014Pleasure conducive to the development\n    of the organs, and to the continuance of their\n    action\u2014Progress of human knowledge\u2014Progress of\n    human happiness                                                 73\n\n\n    CHAPTER IV.\n\n    Relation between the physical condition\n    and happiness, and between happiness and\n    longevity\u2014Longevity a good, and why\u2014Epochs of\n    life\u2014The age of maturity the only one that admits\n    of extension\u2014Proof of this from physiology\u2014Proof\n    from statistics\u2014Explanation of terms\u2014Life a\n    fluctuating quantity\u2014Amount of it possessed in\n    ancient Rome: in modern Europe: at present in\n    England among the mass of the people and among the\n    higher classes                                                 106\n\n\n    CHAPTER V.\n\n    Ultimate elements of which the body is composed\u2014\n    Proximate principles\u2014Fluids and solids\u2014Primary tissues\u2014\n    Combinations\u2014Results\u2014Organs, systems, apparatus\u2014\n    Form of the body\u2014Division into head, trunk, and\n    extremities\u2014Structure and function of each\u2014Regions\u2014\n    Seats of the more important internal organs                   148\n\n\n    CHAPTER VI.\n\n    Of the blood\u2014Physical characters of the blood:\n    colour, fluidity, specific gravity, temperature;\n    quantity\u2014Process of coagulation\u2014Constituents of\n    the blood; proportions \u2014Constituents of the body\n    contained in the blood\u2014Vital properties of the\n    blood\u2014Practical applications                                  334\n\n\n    CHAPTER VII.\n\n    Of the circulation\u2014Vessels connected with the\n    heart; chambers of the heart\u2014Position of the\n    heart\u2014Pulmonic circle; systemic circle\u2014Structure\n    of the heart, artery, and vein\u2014Consequences\n    of the discovery of the circulation to the\n    discoverer\u2014Action of the heart; sounds occasioned\n    by its different movements\u2014Contraction;\n    dilatation\u2014Disposition and action of the\n    valves\u2014Powers that move the blood\u2014Force of\n    the heart\u2014Action of the arterial tubes; the\n    pulse; action of the capillaries; action of the\n    veins\u2014Self-moving power of the blood\u2014Vital\n    endowment of the capillaries; functions\u2014Practical\n    applications                                                   357\n\n\n    FOOTNOTES.                                                     408\n\n\n\n\nINTRODUCTION.\n\n\nThe object of the present work is to give a brief and plain account\nof the structure and functions of the body, chiefly with reference\nto health and disease. This is intended to be introductory to an\naccount of the constitution of the mind, chiefly with reference to\nthe development and direction of its powers. There is a natural\nconnexion between these subjects, and an advantage in studying them\nin their natural order. Structure must be known before function can\nbe understood: hence the science of physiology is based on that of\nanatomy. The mind is dependent on the body: hence an acquaintance with\nthe physiology of the body should precede the study of the physiology\nof the mind. The constitution of the mind must be understood before its\npowers and affections can be properly developed and directed: hence a\nknowledge of the physiology of the mind is essential to a sound view of\neducation and morals.\n\nIn the execution of the first part of this work, that which relates\nto the organization of the body, a formidable difficulty presents\nitself at the outset. The explanation of structure is easy when the\npart described can be seen. The teacher of anatomy finds no difficulty\nin communicating to the student a clear and exact knowledge of the\nstructure of an organ; because, by the aid of dissection, he resolves\nthe various complex substances, of which it is built up, into their\nconstituent parts, and demonstrates the relation of these elementary\nparts to each other. But the case is different with him who attempts\nto convey a knowledge of the structure of an organ merely by the\ndescription of it. The best conceived and executed drawing is a\nmost inadequate substitute for the object itself. It is impossible\nwholly to remove this difficulty: what can be done, by the aid of\nplates, to lessen it, is here attempted. A time may come when the\nobjects themselves will be more generally accessible: meanwhile, the\ndescription now given of the chief organs of the body may facilitate\nthe study of their structure to those who have an opportunity of\nexamining the organs themselves, and will, it is hoped, enable every\nreader at once to understand much of their action.\n\nPhysical science has become the subject of popular attention, and\nmen of the highest endowments, who have devoted their lives to the\ncultivation of this department of knowledge, conceive that they can\nmake no better use of the treasures they have accumulated, than that of\ndiffusing them. Of this part of the great field of knowledge, to make\n\"the rough places plain, and the crooked places straight,\" is deemed a\nlabour second in importance only to that of extending the boundaries of\nthe field itself. But no attempt has hitherto been made to exhibit a\nclear and comprehensive view of the phenomena of life; the organization\nupon which those phenomena depend; the physical agents essential\nto their production, and the laws, as far as they have yet been\ndiscovered, according to which those agents act. The consequence is,\nthat people in general, not excepting the educated class, are wholly\nignorant of the structure and action of the organs of their own bodies,\nthe circumstances which are conducive to their own health, the agents\nwhich ordinarily produce disease, and the means by which the operation\nof such agents may be avoided or counteracted; and they can hardly be\nsaid to possess more information relative to the connexion between the\norganization of the body and the qualities of the mind, the physical\ncondition and the mental state; the laws which regulate the production,\ncombination, and succession of the trains of pleasurable and painful\nthought, and the rules deducible from those laws, having for their\nobject such a determination of voluntary human conduct, as may secure\nthe pleasurable and avoid the painful.\n\nYet nothing would seem a fitter study for man than the nature of man in\nthis sense of the term. A knowledge of the structure and functions of\nthe body is admitted to be indispensable to whoever undertakes, as the\nbusiness of his profession, to protect those organs from injury, and to\nrestore their action to a sound state when it has become disordered;\nbut surely some knowledge of this kind may be useful to those who\nhave no intention to practise physic, or to perform operations in\nsurgery; may be useful to every human being, to enable him to take a\nrational care of his health, to make him observant of his own altered\nsensations, as indications of approaching sickness; to give him the\npower of communicating intelligibly with his medical adviser respecting\nthe seat and the succession of those signs of disordered function, and\nto dispose and qualify him to co-operate with his physician in the use\nof the means employed to avert impending danger, or to remove actual\ndisease.\n\nBut if to every human being occasions must continually occur, when\nknowledge of this kind would be useful, the possession of it seems\npeculiarly necessary to those who have the exclusive care of infancy,\nalmost the entire care of childhood, a great part of the care of\nthe sick, and whose ignorance, not the less mischievous because its\nactivity is induced by affection, constantly endangers, and often\ndefeats, the best concerted measures of the physician.\n\nThe bodily organization and the mental powers of the child depend\nmainly on the management of the infant; and the intellectual and\nmoral aptitudes and qualities of the man have their origin in the\npredominant states of sensation, at a period far earlier in the history\nof the human being than is commonly imagined. The period of infancy is\ndivided by physiologists into two epochs; the first, commencing from\nbirth, extends to the seventh month: the second, commencing from the\nseventh month, extends to the end of the second year, at which time\nthe period of infancy ceases, and that of childhood begins. The first\nepoch of infancy is remarkable for the rapidity of the development\nof the organs of the body: the processes of growth are in extreme\nactivity; the formative predominates over the sentient life, the chief\nobject of the action of the former being to prepare the apparatus\nof the latter. The second epoch of infancy is remarkable for the\ndevelopment of the perceptive powers. The physical organization of\nthe brain, which still advances with rapidity, is now capable of a\ngreater energy, and a wider range of function. Sensation becomes more\nexact and varied; the intellectual faculties are in almost constant\noperation; speech commences, the sign, and, to a certain extent, the\ncause of the growing strength of the mental powers; the capacity of\nvoluntary locomotion is acquired, while passion, emotion, affection,\ncome into play with such constancy and energy, as to exert over the\nwhole economy of the now irritable and plastic creature a prodigious\ninfluence for good or evil. If it be, indeed, possible to make correct\nmoral perception, feeling, and conduct, a part of human nature, as much\na part of it as any sensation or propensity\u2014if this be possible for\nevery individual of the human race, without exception, to an extent\nwhich would render _all_ more eminently and consistently virtuous than\n_any_ are at present (and of the possibility of this, the conviction\nis the strongest in the acutest minds which have studied this subject\nthe most profoundly), preparation for the accomplishment of this object\nmust be commenced at this epoch. But if preparation for this object\nbe really commenced, it implies, on the part of those who engage in\nthe undertaking, some degree of knowledge; knowledge of the physical\nand mental constitution of the individual to be influenced; knowledge\nof the mode, in which circumstances must be so modified in adaptation\nto the nature of the individual being, as to produce upon it, with\nuniformity and certainty, a given result. The theory of human society,\naccording to its present institutions, supposes that this knowledge is\npossessed by the mother; and it supposes, further, that this adaptation\nwill actually take place in the domestic circle through her agency.\nHence the presumed advantage of having the eye of the mother always\nupon the child; hence the apprehension of evil so general, I had almost\nsaid instinctive, whenever it is proposed to take the infant, for the\npurpose of systematic physical and mental discipline, from beyond the\nsphere of maternal influence. But society, which thus presumes that\nthe mother will possess the power and the disposition to do this, what\nexpedients has it devised to endow her with the former, and to secure\nthe formation of the latter? I appeal to every woman whose eye may\nrest on these pages. I ask of you, what has ever been done for you to\nenable you to understand the physical and mental constitution of that\nhuman nature, the care of which is imposed upon you? In what part of\nthe course of your education was instruction of this kind introduced?\nOver how large a portion of your education did it extend? Who were\nyour teachers? What have you profited by their lessons? What progress\nhave you made in the acquisition of the requisite information? Were\nyou at this moment to undertake the guidance of a new-born infant to\nhealth, knowledge, goodness, and happiness, how would you set about\nthe task? How would you regulate the influence of external agents upon\nits delicate, tender, and highly-irritable organs, in such a manner\nas to obtain from them healthful stimulation, and avoid destructive\nexcitement? What natural and moral objects would you select as the best\nadapted to exercise and develope its opening faculties? What feelings\nwould you check, and what cherish? How would you excite aims; how would\nyou apply motives? How would you avail yourself of pleasure as a final\nend, or as the means to some further end? And how would you deal with\nthe no less formidable instrument of pain? What is your own physical,\nintellectual, and moral state, as specially fitting you for this\noffice? What is the measure of your own self-control, without a large\nportion of which no human being ever yet exerted over the infant mind\nany considerable influence for good? There is no philosopher, however\nprofound his knowledge, no instructor, however varied and extended his\nexperience, who would not enter upon this task with an apprehension\nproportioned to his knowledge and experience; but knowledge which men\nacquire only after years of study, habits which are generated in men\nonly as the result of long-continued discipline, are expected to come\nto you spontaneously, to be born with you, to require on your part no\nculture, and to need no sustaining influence.\n\nBut, indeed, it is a most inadequate expression of the fact, to say\nthat the communication of the knowledge, and the formation of the\nhabits which are necessary to the due performance of the duties of\nwomen, constitute no essential part of their education: the direct\ntendency of a great part of their education is to produce and foster\nopinions, feelings, and tastes, which positively disqualify them for\nthe performance of their duties. All would be well if the marriage\nceremony, which transforms the girl into the wife, conferred upon the\nwife the qualities which should be possessed by the mother. But it is\nrare to find a person capable of the least difficult part of education,\nnamely, that of communicating instruction, even after diligent study,\nwith a direct view to teaching; yet an ordinary girl, brought up in\nthe ordinary mode, in the ordinary domestic circle, is intrusted with\nthe direction and control of the first impressions that are made upon\nthe human being, and the momentous, physical, intellectual, and moral\nresults that arise out of those impressions!\n\nI am sensible of the total inadequacy of any remedy for this\nevil, short of a modification of our domestic institutions. Mere\ninformation, however complete the communication of it, can do little\nbeyond affording a clearer conception of the end in view, and of\nthe means fitted to secure it. Even this little, however, would be\nsomething gained; and the hope of contributing, in some degree, to\nthe furtherance of this object, has supplied one of the main motives\nfor undertaking the present work. Meantime, women are the earliest\nteachers; they must be nurses; they can be neither, without the risk\nof doing incalculable mischief, unless they have some understanding\nof the subjects about to be treated of. On these grounds I rest their\n_obligation_ to study them; and I look upon that notion of delicacy,\nwhich would exclude them from knowledge calculated, in an extraordinary\ndegree, to open, exalt, and purify their minds, and to fit them for the\nperformance of their duties, as alike degrading to those to whom it\naffects to show respect, and debasing to the mind that entertains it.\n\nThough each part of this work will be made as complete in itself as\nthe author is capable of rendering it, and to that extent independent\nof any other part, yet there will be found to be a strict connexion\nbetween the several portions of the whole; and greatly as the topics\nincluded in the latter differ from those which form the earlier\nsubjects, the advantage of having studied the former before the latter\nare entered on, will be felt precisely as the word _study_ can be\njustly applied to the operation of the mind on such matters.\n\nIn the expository portion of the work I have not been anxious to\nabstain from the employment of technical terms, when a decidedly useful\npurpose was to be obtained by the introduction of them; but I have been\nvery careful to use no such term without assigning the exact meaning\nof it. A technical term unexplained is a dark spot on the field of\nknowledge; explained, it is a clear and steady light.\n\nIn order really to understand the states of health and disease,\nan acquaintance with the nature of organization, and of the vital\nprocesses of which it is the seat and the instrument, is indispensable:\nit is for this reason that the exposition of structure and function,\nattempted in this first part of the work, is somewhat full; but there\ncannot be a question that, if it accomplish its object, it will not\nonly enable the account of health and disease in the subsequent part of\nit to be much more brief, but that it will, at the same time, render\nthat account more intelligible, exact, and practical.\n\n  S. S.\n\n\n\n\nTHE\n\nPHILOSOPHY OF HEALTH.\n\n\n\n\nCHAPTER I.\n\n  Characters by which living beings are distinguished\n  from inorganic bodies\u2014Characters by which animals are\n  distinguished from plants\u2014Actions common to plants and\n  animals\u2014Actions peculiar to animals\u2014Actions included in the\n  organic circle\u2014Actions included in the animal circle\u2014Organs\n  and functions defined\u2014Action of physical agents on\n  organized structures\u2014Processes of supply, and processes\n  of waste\u2014Reasons why the structure of the animal is more\n  complex than that of the plant.\n\n\nThe distinction between a living being and an inorganic body,\nbetween a plant and a stone, is, that the plant carries on a number\nof processes which are not performed by the stone. The plant absorbs\nfood, converts its food into its own proper substance, arranges this\nsubstance into bark, wood, vessels, leaves, and other organized\nstructures; grows, arrives at maturity, and decays; generates and\nmaintains a certain degree of heat; derives from a parent the primary\nstructure and the first impulse upon which these varied actions depend;\ngives origin to a new being similar to itself, and, after a certain\ntime, terminates its existence in death.\n\nNo such phenomena are exhibited by the stone; it neither absorbs\nfood, nor arranges the matter of which it is composed into organized\nstructure; nor grows, nor decays, nor generates heat, nor derives its\nexistence from a parent, nor gives origin to a new being, nor dies.\nNothing analogous to the processes by which these results are produced,\nis observable in any body that is destitute of life; all of them are\ncarried on by every living creature. These processes are, therefore,\ndenominated vital, and, being peculiar to the state of life, they\nafford characters by which the living being is distinguished from the\ninorganic body.\n\nIn like manner the distinction between an animal and a plant is, that\nthe animal possesses properties of which the plant is destitute. It is\nendowed with two new and superior powers, to which there is nothing\nanalogous in the plant; namely, the power of sensation, and the power\nof voluntary motion; the capacity of feeling, and the capacity of\nmoving from place to place as its feeling prompts. The animal, like\nthe plant, receives food, transforms its food into its own proper\nsubstance, builds this substance up into structure, generates, and\nmaintains a certain temperature, derives its existence from a parent,\nproduces an offspring like itself, and terminates its existence in\ndeath. Up to this point the vital phenomena exhibited by both orders of\nliving creatures are alike: but at this point the vital processes of\nthe plant terminate, while those of the animal are extended and exalted\nby the exercise of the distinct and superior endowments of sensation\nand voluntary motion. To feel, and to move spontaneously, in accordance\nwith that feeling, are properties possessed by the animal, but not by\nthe plant; and therefore these properties afford characters by which\nthe animal is distinguished from the plant.\n\nThe two great classes of living beings perform, then, two distinct\nsets of actions: the first set is common to all living creatures; the\nsecond is peculiar to one class: the first set is indispensable to\nlife; the second is necessary only to one kind of life, namely, the\nanimal. The actions included in the first set, being common to all\nliving or organized creatures, are called ORGANIC; the actions included\nin the second class, belonging only to one part of living or organized\ncreatures, namely, animals, are called ANIMAL. The ORGANIC actions\nconsist of the processes by which the existence of the living being is\nmaintained, and the perpetuation of its species secured: the ANIMAL\nactions consist of the processes by which the living being is rendered\npercipient, and capable of spontaneous motion. The ORGANIC processes\ncomprehend those of nutrition, respiration, circulation, secretion,\nexcretion, and reproduction; the first five relate to the maintenance\nof the life of the individual being; the last to the perpetuation of\nits species. The ANIMAL processes comprehend those of sensation and\nof voluntary motion, often denominated processes of relation, because\nthey put the individual being in communication with the external\nworld. There is no vital action performed by any living creature\nwhich may not be included in one or other of these processes, or in\nsome modification of some one of them. There is no action performed\nby any inorganic body which possesses even a remote analogy to either\nof these vital processes. The line of demarcation between the organic\nand the inorganic world is, therefore, clear and broad; and the line\nof demarcation between the two great divisions of the organic world,\nbetween the inanimate and the animate, that is, between plants and\nanimals, is no less decided: for, of the two sets of actions which have\nbeen enumerated, the one, as has just been stated, is common to the\nwhole class of living beings, while the second set is peculiar to one\ndivision of that class. The plant performs only the organic actions:\nall the vital phenomena it exhibits are included in this single circle;\nit is, therefore, said to possess only organic life: but the animal\nperforms both organic and animal actions, and is therefore said to\npossess both organic and animal life.\n\nBoth the organic and the animal actions are accomplished by means\nof certain instruments, that is, organized bodies which possess a\ndefinite structure, and which are moulded into a peculiar form. Such\nan instrument is called an organ, and the action of an organ is called\nits function. The leaf of the plant is an organ, and the conversion\nof sap by the leaf into the proper juice of the plant, by the process\ncalled respiration, is the function of this organ. The liver of the\nanimal is an organ; and the conversion of the blood that circulates\nthrough it into bile, by the process of secretion, is its function. The\nbrain is an organ; the sentient nerve in communication with it is also\nan organ. The extremity of the sentient nerve receives an impression\nfrom an external object, and conveys it to the brain, where it becomes\na sensation. The transmission of the impression is the function of\nthe nerve; the conversion of the impression into a sensation is the\nfunction of the brain.\n\nThe living body consists of a congeries of these instruments or\norgans: the constituent matter of these organs is always partly in a\nfluid and partly in a solid state. Of the fluids and solids which thus\ninvariably enter in combination into the composition of the organs, the\nfluids may be regarded as the primary and essential elements, for they\nare the source and the support of the solids. There is no solid which\nis not formed out of a fluid; no solid which does not always contain,\nas a constituent part of it, some fluid, and none which is capable of\nmaintaining its integrity without a continual supply of fluids.\n\nWhatever be the intimate composition of the fluids out of which the\nsolids are formed, the investigation of which is more difficult than\nthat of the solids and the nature of which is therefore less clearly\nascertained, it is certain that all the matter which enters into\nthe composition of the solid is disposed in a definite order. It is\nthis disposition of the constituent matter of the living solid in a\ndefinite order that constitutes the arrangement so characteristic of\nall living substance. Definite arrangements are combined in definite\nmodes, and the result is what is termed organization. From varied\narrangements result different kinds of organized substances, each\nendowed with different properties, and exhibiting peculiar characters.\nBy the recombination of these several kinds of organized substances,\nin different proportions and different modes, are formed the special\ninstruments, or organs, of which we have just spoken; while it is the\ncombining, or the building up of these different organized substances\ninto organs, that constitutes structure.\n\nIn the living body, not only is each distinct organ alive, but, with\nexceptions so slight that they need not be noticed here, every solid\nwhich enters into the composition of the organ is endowed with vital\nproperties. This is probably the case with the primary substances or\ntissues which compose the several organs of the plant; but that the\nanimal solids are alive is indubitable; nay, the evidence is complete,\nthat many even of the animal fluids possess vitality. The blood in the\nanimal is as truly alive as the brain, and the bone as the flesh. The\norganized body, considered as a whole, is the seat of life; but life\nalso resides in almost every component part of it.\n\nYet the matter out of which these living substances is formed is not\nalive. By processes of which we know nothing, or, at least, of which\nwe see only the first steps,\u2014matter, wholly destitute of life, is\nconverted into living substance. The inorganic matter, which is the\nsubject of this wonderful transformation, is resolvable into a very\nfew elementary substances. In the plant, these substances consist of\nthree only, namely, oxygen, hydrogen, and carbon. The first two are\na\u00ebriform or gaseous bodies; the last is a solid substance, and it is of\nthis that the plant is chiefly composed: hence the basis of the plant\nis a solid. The elementary bodies, into which all animal substance is\nresolvable, are four, namely, azote, oxygen, hydrogen, and carbon.\nInto every animal fluid and solid this new substance azote enters so\nlargely, that it may be considered as the fundamental and distinctive\nelement of the animal organization: hence the basis of the animal is\nan a\u00ebriform or gaseous fluid. The animal is composed of air, the plant\nof solid matter; and this difference in their elementary nature gives\norigin to several distinctive characters between the plant and the\nanimal, in addition to those which have been already stated.\n\nThus the characters of the plant are solidity, hardness, fixedness, and\ndurability; while the animal is comparatively fluid, soft, volatile,\nand perishable; and the reason is now manifest. The basis of the animal\nbeing an a\u00ebriform fluid, its consistence is softer than that of the\nplant, the basis of which is a firm solid; and, at the same time, the\ncomponent elements of the animal being more numerous than those of the\nplant, and the fluidity of these elements, and of the compounds they\nform, greatly favouring their action and reaction on each other and on\nexternal agents, the animal body is more volatile and perishable during\nlife, and more readily decomposed after death.\n\nIt has been stated, that the object of every structure or organ\nof the living body, is the performance of some special action or\nfunction,\u2014the ultimate object of the fluids being the production of\nthe solids; the ultimate object of the solids being the formation of\norgans; the ultimate object of organs being the performance of actions\nor functions; while it is in the performance of actions or functions\nthat life consists. Functions carried on by organs; organs in action;\nspecial organs performing definite actions, this it is that constitutes\nthe state of life. Every particle of matter which enters into the\ncomposition of the living body has thus its own place, forming, or\ndestined to form, a constituent part of some organ; every organ has\nits own action; all the organs of the body form the body; and all\nthe actions of all the organs constitute the aggregate of the vital\nphenomena.\n\nEvery organ is excited to action, or its function is called into\noperation by means of some external body. The external bodies capable\nof exciting and maintaining the functions of living organs, consist\nof a definite class. Because these bodies belong to that department\nof science which is called physical, they are termed physical agents.\nThey are air, water, heat, cold, electricity, and light. Without the\nliving organ, the physical agent can excite no vital action: without\nthe physical agent, the living organ can carry on no vital process.\nThe plant cannot perform the vital process of respiration without the\nleaf, nor, with the leaf, without air. The physical agent acts upon the\nliving organ; the living organ reacts upon the physical agent, and the\naction between both is definite. In the lung of the animal a certain\nprinciple of the air unites, in definite proportions, with a certain\nprinciple of the blood; the oxygen of the air combines with the carbon\nof the blood; the air is changed by the abstraction of its oxygen;\nthe blood is changed by the abstraction of its carbon. Atmospheric\nair goes to the lung, but atmospheric air does not return from the\nlung; it is converted into a new substance by the action of the organ:\nit is changed into carbonic acid by the union of a given quantity of\noxygen, which it transmits to the organ, with a given quantity of\ncarbon which the organ conveys to it. Venous blood goes to the lung,\nbut venous blood does not return from the lung; it is converted, by\nthe instrumentality of the organ, into a new substance, into arterial\nblood, by giving to the air carbon, and by receiving from the air\noxygen. In this manner the change in the physical agent is definite and\nuniform; and the change in the living substance is equally definite and\nuniform.\n\nIt is this determinate interchange of action between the living organ\nand the physical agent that constitutes what is termed a vital process.\nAll vital processes are carried on by living organs; the materials\nemployed in all vital processes are physical agents; the processes\nthemselves are vital functions. All the changes produced by all the\norgans of the plant upon physical agents, and all the changes produced\nby all physical agents upon the organs of the plant, constitute all\nthe vital processes of the plant\u2014comprehend the whole sum of its\nvital phenomena. The root, the trunk, the woody substance, the bark,\nthe ascending vessels bearing sap, the descending vessels bearing\nsecreted fluids, the leaves, the flowers, these are the living organs\nof the plant. Air, water, heat, cold, electricity, light, these are the\nphysical agents which produce in these organs definite changes, and\nwhich are themselves changed by them in definite modes; and the whole\nof these changes, taken together, comprehend the circle of actions, or\nthe range of functions performed by this living being.\n\nIn the state of life, during the interchange of action which thus\nincessantly goes on between physical agents and vital organs, the\nlaws to which inorganic matter is subject are resisted, controlled,\nand modified. Physical and chemical attractions are brought under the\ninfluence of a new and superior agency, with the laws of which we are\nimperfectly acquainted, but the operation of which we see, and which we\ncall the agency of life. Air, water, heat, electricity, are physical\nagents, which subvert the most intimate combinations of inorganic\nbodies, resolving them into their simple elements, and recombining\nthese elements in various modes, and thus forming new bodies, endowed\nwith totally different properties; but the physical and chemical\nagencies by which these changes are wrought in the inorganic, are\nresisted, controlled, and modified by the living body: resisted, for\nthese physical agents do not decompose the living body; controlled\nand modified, for the living body converts these very agents into the\nmaterial for sustaining its own existence Of all the phenomena included\nin that circle of actions which we designate by the general term life,\nthis power of resisting the effects universally produced by physical\nagents on inorganic matter, and of bringing these very agents under\nsubjection to a new order of laws, is one of the most essential and\ndistinctive.\n\nAll vital processes are processes of supply, or processes of waste. By\nevery vital action performed by the organized body, some portion of its\nconstituent matter is expended. Numerous vital actions are constantly\ncarried on for the sole purpose of compensating this expenditure. Every\nmoment old particles are carried out of the system; every moment new\nparticles are introduced into it. The matter of which the organized,\nand more especially the animal, body is composed, is thus in a state\nof perpetual flux; and in a certain space of time it is completely\nchanged, so that of all the matter that constitutes the animal body at\na given point of time, not a single particle remains at another point\nof time at a given distance.\n\nAll the wants of the economy of the plant are satisfied by a due\nsupply of air, water, heat, cold, electricity, and light. Some of\nthese physical agents constitute the crude aliment of the plant;\nothers produce in this aliment a series of changes, by which it is\nconverted from crude aliment into proper nutriment, while others act\nas stimulants, by which movements are excited, the ultimate object of\nwhich is the distribution of the nutriment to the various parts of the\neconomy of the plant.\n\nThe same physical agents are indispensable to the support of the animal\nbody; but the animal cannot be sustained by these physical agents\nalone; for the maintenance of animal life, in some shape or other,\nvegetable or animal matter, or both in a certain state of combination,\nmust be superadded: hence another distinction between the plant and the\nanimal,\u2014the necessity, on the part of the animal, of an elaborated\naliment to maintain its existence. By the vital processes of its\neconomy, the plant converts inorganic into organic matter; by the vital\nprocesses of its economy, the animal converts matter, already rendered\norganic, into its own proper substance. The plant is thus purveyor to\nthe animal: but it is more than purveyor to it; for while it provides,\nit also prepares its food; it saves the animal one process, that of\nthe transmutation of inorganic into organic matter. The ultimate end,\nor the final cause of the vital processes performed by the first class\nof living beings, is thus the elaboration of aliment for the second:\nthe inferior life is spent in ministering, and the great object of its\nbeing is to minister to the existence of the superior.\n\nAt the point at which organization commences structure is so simple\nthat there is no manifest distinction of organs. Several functions are\nperformed apparently by one single organized substance. The lowest\nplants and the lowest animals are equally without any separate organs,\nas far as it is in our power to distinguish them, for carrying on the\nvital actions they perform. An organized tissue, apparently of an\nhomogeneous nature, containing fluid matter, is all that can be made\nout by which the most simply-constructed plant carries on its single\nset, and by which the most simply-constructed animal carries on its\ndouble set, of actions. But this simplicity of structure exists only\nat the very commencement of the organized world. Every advancement in\nthe scale of organization is indicated by the construction of organs\nmanifestly separate for the performance of individual functions;\nand, invariably, the higher the being, the more complete is this\nseparation of function from function, and, consequently, the greater\nthe multiplication of organs, and the more elaborate and complex the\nstructure;\u2014and hence another distinction between the plant and the\nanimal. The simplicity of the structure of the plant is in striking\ncontrast to the complexity of the structure of the animal; and this\ndifference is not arbitrary; it is a matter of absolute necessity, and\nthe reason of this necessity it will be instructive to contemplate.\n\nThe plant, as has been shown, performs only one set of functions, the\norganic; while the animal performs two sets of functions, the organic\nand the animal. The animal, then, performs more functions than the\nplant, and functions of a higher order; it carries on its functions\nwith a greater degree of energy; its functions have a more extended\nrange, and all its functions bear a certain relation to each other,\nmaintaining an harmonious action. The number, the superiority, the\nrelation, the range, and the energy of the functions performed by\nthe animal are, then, so many conditions, which render it absolutely\nindispensable that it should possess a greater complexity of structure\nthan the plant.\n\n1. To build up structure is to create, to arrange, and to connect\norgans. Organs are the instruments by which functions are performed,\nand without the instrument there can be no action. With as many\nmore organs than the plant possesses the animal must, therefore, be\nprovided, as are necessary to carry on the additional functions it\nperforms. Organs, for its organic functions, it must have as well as\nthe plant; but to these must be superadded organs of another class, for\nwhich the plant has no need, namely, organs for its animal functions.\nTwo sets of organs must, therefore, be provided for the animal, while\nthe plant requires but one.\n\n2. Some functions performed by the animal are of a higher order than\nany performed by the plant, and the superior function requires a higher\norganization. The construction of an organ is complex as its action is\nelevated; the instrument is elaborately prepared in proportion to the\nnobleness of its office.\n\n[Illustration: Fig. I.]\n\n[Illustration: Fig. II.]\n\n[Illustration: Fig. III.]\n\n[Illustration: Fig. IV.]\n\n3. But this is not all; for the addition of a superior function\nrequires not only the addition of an organ having a corresponding\nsuperiority of structure, but it requires, further, that a certain\nelevation of structure should be communicated to all the organs of\nall the inferior functions, on account of the relation which it is\nnecessary to establish between function and function. Unless the organ\nof an inferior function be constructed with a perfection corresponding\nto that of the organ of a superior function, the inferior will be\nincapable of working in harmony with the superior. Take, for example,\nthe inferior function of nutrition: nutrition is an organic function\nequally necessary to the plant and to the animal, and requiring in\nboth organs for performing it; but this function cannot be performed\nin the animal by organs as simple as suffice for the plant. Nutrition,\nin the plant, is carried on in the following mode:\u2014The root of the\nplant is divided, like the trunk, into numerous branches (fig. I. 1).\nThese branches divide and subdivide into smaller and smaller branches,\nuntil at last they reach an extreme degree of minuteness (fig. I. 2 2).\nThe smallest of these divisions, called, from their hair-like tenuity,\n_capillary_ (fig. I. 2 2), are provided with a peculiar structure,\nwhich is endowed with a specific function. In most plants this peculiar\nstructure is found at the terminal point of the rootlet (fig. I. 2 2);\nbut in some plants the capillary branches of the rootlets are provided\nwith distinct bodies (fig. II. 1 2), scarcely to be discerned when\nthe root has been removed some time from the soil, and has become dry\n(fig. II. 2 2); but which, in a few minutes after the root has been\nplunged in water, provided the plant be still alive, become turgid with\nfluid, and, consequently, distinctly visible (fig. II. 1 1 1). These\nbodies, when they exist, or the terminal point of the rootlet when\nthese bodies are absent, are termed _spongeol\u00e6_, or spongeoles; and the\nstructure and function of the organ, in both cases, are conceived to\nbe precisely the same. In both the organ consists of a minute cellular\nstructure. Fig. III. 1, shows this structure as it appears when the\nobject is magnified. The office of this organ is to absorb the aliment\nof the plant from the soil; and so great is its absorbing power, that,\nas is proved by direct experiment, it absorbs the colouring molecules\nof liquids, though these molecules will not enter the ordinary pores,\nwhich are of much greater magnitude. With the spongeoles are connected\nvessels which pass through the substance of the stem or trunk to the\nleaf. Fig. III. 2, shows these tubes springing from the cellular\nstructure of the spongeole, and passing up to the stem or trunk. Fig.\nIV. 2, exhibits a magnified view of the appearance of the mouths of\nthese tubes on making an horizontal section of the spongeole. Fig. V.\n1 1 1, exhibits a view of these tubes passing to the leaf. Figs. VI.\nand VII. 1 1 1 1, show these vessels spread out upon, and ramifying\nthrough, the leaf. The crude aliment, borne by these tubes to the leaf,\nis there converted into proper nutriment; and from the leaf, when\nduly elaborated, this proper nutriment is carried out by ducts to the\nvarious organs of the plant, in order to supply them with the aliment\nthey need.\n\n[Illustration: Fig. V.]\n\nNow, for carrying on the process of nutrition in this mode, there\nmust be organs to absorb the crude aliment, organs to convey the crude\naliment to the laboratory, the leaf, in which it is converted into\nproper nutriment; and, finally, organs for carrying out this proper\nnutriment to the system. Complication of structure, to this extent, is\nindispensable; and, accordingly, with spongeol\u00e6, with sap-vessels, with\nleaves, with distributive ducts, the plant is provided. Without all the\nparts of this apparatus it could not carry on its function: any further\ncomplication would be useless.\n\n[Illustration: Fig. VI.]\n\nBut, suppose a new and superior function to be added to the plant;\nsuppose it to be endowed with the power of locomotion, what would be\nthe consequence of communicating to it this higher power? That its\nformer state of simplicity would no longer suffice for the inferior\nfunction. Why? because the exercise of the superior would interrupt\nthe action of the inferior function. Nutrition by imbibition, and\nthe exercise of locomotion, cannot go on simultaneously in the same\nbeing. The plant is fixed in the soil by its roots; and from this, its\nstate of immobility, results this most important consequence, that its\nspongeol\u00e6 are always in contact with its food.\n\n[Illustration: Fig. VII.]\n\n[Illustration: Fig. VIII.]\n\nBut we may imagine a plant not fixed to the soil; a plant so\nconstituted as to be capable of moving from place to place; such a\nplant would not be always in contact with its food, and therefore, as\nit exercised its faculty of locomotion, it could not but interrupt\nor suspend its function of nutrition. In a being capable of carrying\non these two functions simultaneously, the entire apparatus of the\nfunction of nutrition must then be modified. Instead of having\nspongeol\u00e6 fixed immovably in the earth, and spread out in a soil\nadapted to transmit to these organs nutrient matter in a state fitted\nfor absorption, it must be provided with a reservoir for containing\nits food, in order that it may carry its aliment about with it in\nall its changes of place. And such is the modification uniformly\nfound in all animals: an internal reservoir for containing its food\nis provided, perhaps, for every animal without exception. Even the\nsimplest and minutest creatures with which the microscope has made\nus acquainted, the lowest tribes of the Infusoria (fig. VIII.), the\nsentient, self-moving cellules, placed at the very bottom of the\nanimal scale, possess this modification of structure. For a long\ntime it was conceived that these minute and simple creatures were\nwithout distinction of parts, that they had no separate organs for the\nreception and digestion of their food; that they absorbed their aliment\nthrough the porous tissue of which their body is composed; that thus,\ninstead of having a separate stomach, their entire body is a stomach,\nand instead of having even as much as a separate organ for absorption,\nlike the more perfect plant, the whole body might be considered as a\nsingle spongeole.\n\nBut, by a simple and beautiful experiment, a German physiologist\nhas shown the incorrectness of this opinion, and has established the\nfact, that the distinction between the plant and the animal, here\ncontended for, is found even at the very lowest point of the animal\nscale. Like other physiologists, conceiving that the difficulty of\ndiscovering the structure of the lower tribes of the animalculi\nmight be owing to the transparency or the tissues of which they are\ncomposed, it struck Ehrenberg, that if he could feed them with coloured\nsubstances, he might obtain some insight into their organization.\nIn his first endeavours to accomplish this object he failed, for he\nemployed the pigments in ordinary use; but either the animals would not\ntouch aliment thus adulterated, or those that did so were instantly\nkilled. It then occurred to him, that these colours are adulterated\nwith lead and other substances, in all probability noxious to the\nlittle subjects of his experiment. \"What I require,\" said he, \"is some\nvegetable or animal colouring matter perfectly pure.\" He then tried\nperfectly pure indigo and perfectly pure carmine. His success was\nnow complete: in a minute or two, after mixing with their food pure\nvegetable colouring matter, he observed in the interior of the body of\nthese creatures minute spots of a definite figure, and of the colour\nof the pigment employed (fig. VIII. 1 1 1 1). The form and magnitude\nof these spots were different in different tribes, but the same in the\nsame individual, and even in the same species (fig. IX. 1 1, fig. X.\n1 1). No other parts of the body were tinged with the colour, though\nthe animals remained in the coloured fluid for days together. This was\ndecisive. This physiologist had now obtained an instrument capable of\nrevealing to him the interior organization of a class of beings, the\nstructure of which had heretofore been wholly unknown. On applying\nit to the MONAS TERMO (fig. VIII.), the animated point, or cellule,\nwhich stands at the bottom of the animal scale, he discovered, in the\nposterior portion of its body, several coloured spots which constitute\nits stomachs (fig. VIII. 1 1 1 1). The different situations and\ndifferent forms of the stomach in different tribes of these creatures,\nare represented by the coloured portions (fig. VIII. 1, fig. IX. 1,\nfig. X. 1), in which the currents of fluid flowing to their mouths\nare seen (fig. IX. 2, fig. X. 2). These experiments go far towards\nestablishing the fact, that every animal, even the very lowest, has an\nexternal mouth and an internal stomach, and that it takes its food by\nan act of volition.\n\n[Illustration: Fig. IX.]\n\n[Illustration: Fig. X.]\n\nBut if the proof of this must be admitted to be still imperfect\nwith regard to the lowest tribes of animals, it is certain that, as\nwe ascend in the scale of organization, the nutritive apparatus is\nuniformly arranged in this mode. Every animal of every class large\nenough to be distinctly visible, and the structure of which is not\nrendered inappreciable by the transparency of its solids and fluids, is\nmanifestly provided with a distinct internal reservoir for containing\nits food. On the internal surface of this reservoir open the mouths of\nvessels, minute in size but countless in number, which absorb the food\nfrom the stomach.\n\nFig. XI. shows these vessels opening on the inner surface of the\nstomach, the white points representing their mouths, turgid with the\nfood they have absorbed. Fig. XII. exhibits magnified views of the same\nvessels, the points representing their open mouths, and the lines the\nvessels themselves in continuation with their mouths. Fig. XIII. shows\nthe appearance of the inner surface of the intestine soon after the\nanimal has taken food; the smaller white lines (1 1 1 1) representing\nthe absorbent vessels full of digested food, and the larger lines (2 2\n2 2) the trunks of the absorbent vessels formed by the union of many of\nthe smaller.\n\n[Illustration: Fig. XI.]\n\n[Illustration: Fig. XII.]\n\nFrom this account, it is clear that the absorbing vessels of the\nstomach perform an office precisely analogous to that of the spongeoles\nof the root. What the soil is to the plant, the stomach is to the\nanimal. The absorbing vessels diffused through the stomach, as long\nas the stomach contains food, are in exactly the same condition as\nthe spongeoles of the root spread out in the soil; and the absorbing\nvessels of the stomach are as much and as constantly in contact with\nthe aliment, which it is their office to take into the system, as the\nspongeoles of the root. Such, then, is the expedient adopted to render\nthe function of nutrition compatible with the function of locomotion.\nA reservoir of food is placed in the interior of the animal, provided\nwith absorbent vessels which are always in contact with the aliment. In\nthis mode, contact with aliment is not disturbed by continual change of\nplace; the organic process is not interrupted by the exercise of the\nanimal function.\n\n[Illustration: Fig. XIII.]\n\nBut the more elaborate organization which it is necessary to impart\nto the apparatus of the inferior function, in consequence of the\ncommunication of a superior faculty, is not completed simply by the\naddition of this new organ, the stomach. Other complications are\nindispensable; for if food be contained in an isolated organ, placed in\nthe interior of the body, means must be provided for conveying the food\ninto this organ; hence the necessity of an apparatus for deglutition.\nMoreover, the food having been conveyed to the stomach, and having\nundergone there the requisite changes, means must next be provided for\nconveying it from the stomach to the other parts of the body; hence\nthe necessity of an apparatus for the circulation. But food, however\nelaborately prepared by the stomach, is incapable of nourishing the\nbody, until it has been submitted to the action of atmospheric air;\nhence the necessity of an additional apparatus, either for conveying\nfood to the air, or for transmitting air to the food, or for bringing\nboth the food and the air into contact in the same organ. And, when\nstructure after structure has been built up, in order to carry on this\nextended series of processes, the number of provisions required is\nnot even yet complete; for of the most nutritious fond the whole mass\nis not nutritive; and even the whole of that portion of it which is\nactually applied to the purpose of nutrition, becomes, after a time,\nworn out, and must be removed from the system; hence the necessity of a\nfurther apparatus for excretion.\n\nThat nutrition and locomotion may go on together, it is clear, then,\nthat there must be provided a distinct apparatus for containing\nfood, a distinct apparatus for deglutition, a distinct apparatus for\ncirculation, a distinct apparatus for respiration, a distinct apparatus\nfor excretion, and so on; and that, in this manner, the communication\nof a single function of a superior order renders a modification not\nmerely of one but of many inferior functions absolutely indispensable,\nin order to adjust the one to the other, and to enable them to act in\nharmony.\n\nBut the necessary complication of structure does not stop even here;\nfor the communication of one function of a superior order imposes\nthe necessity of communicating still another. Locomotion cannot be\nexercised without perception; sensation is indispensable to volition,\nand volition, of course, to voluntary motion. A being endowed with\nthe power of moving from place to place, without possessing the power\nof perceiving external objects, must be speedily destroyed. The\ncommunication of sensation to a creature fixed immovably to a single\nspot, conscious of the approach of bodies, but incapable of avoiding\ntheir contact, would be not only useless but pernicious, since it\nwould be to make a costly provision for the production of pain, and\nnothing else; but the communication of locomotion without sensation\nwould be as unwisely defective, as the former would be perniciously\nexpensive; since it would be to endow a being with a faculty, the\nexercise of which would be fatal to it for the want of a second faculty\nto guide the first. Nor could the possession of locomotion, without the\nfurther possession of sensation, be otherwise than fatal, for another\nreason. Consciousness is not necessary to nutrition as performed by\nthe plant, but it is indispensable to nutrition as performed by the\nanimal: for if the food of the animal be not always on the same spot\nwith itself; if it be under the necessity of searching for it, and of\nconveying it, when found, into the interior of its body, it must, of\ncourse, possess the power of perceiving it when within its reach, and\nof apprehending and appropriating it by an act of volition, of none of\nwhich actions is it capable without the possession of sensation. Again,\nthen, we see that, in order to secure harmonious action, function must\nbe put in relation with function. In order to prevent jarring and\nmutually-destructive action, function must be superadded to function,\nand throughout the animal creation the complication of structure, which\nis necessary for the accomplishment of these ends, is given without\nparsimony, but without profusion: nothing is given which is not needed,\nnothing is withheld which is required.\n\n4. As we ascend in the scale of organization, numerous functions being\ncarried on, and numerous organs constructed for performing them, it\nis obvious that the range of each function must be proportionally\nextended; the range necessarily increasing with the multiplication\nof organ and function: and this is another cause of the unavoidable\ncomplication of structure. Slight consideration will suffice to show\nthe necessary connexion between an extended range of action and\ncomplication of structure. Take, as an example, the organic function\nof respiration: respiration is the function by which air is brought\ninto contact with food; it is the completion of digestion. The sole\nend of all the apparatus that belongs to this function is to bring the\nair and the food into a certain degree of proximity. Now, when all the\nsubstances that enter into the composition of the body of an animal are\nslight, delicate, and permeable to air (as in fig. XIV.), and when the\nbody is always surrounded by air, air must at all times be in contact\nwith the particular organ that contains the food, no less than with\nthe general system to which the food is distributed. In this case, to\nconstruct a separate apparatus for containing air would be useless,\nbecause wherever food is, there air must be, since it constantly\npermeates every part of the body.\n\n[Illustration: Fig. XIV.]\n\nWhen, on the other hand, the tissues are so firm and dense as to be\nimpermeable; when they are folded into bulky and complex organs, and\nwhen these organs are placed in situations to which the external air\ncannot reach, the construction of a separate apparatus for respiration\nis indispensable. The respiratory apparatus consists either of organs\nfor carrying air to the food, or of organs for carrying food to the\nair. The one or the other is adopted, according to the nature of the\nbody. If the size of the animal be small; if the tissues which form\nthe solid portion of its body be delicate in texture; if, at the same\ntime, the wants of its economy require that its food should be highly\na\u00ebrated (for there is the closest connexion between energy of function\nand perfect a\u00ebration of the food), an apparatus of sufficient magnitude\nto a\u00ebrate the food in a high degree would occupy the entire bulk of the\nbody. In such a case, it is easier to carry air to the food than food\nto the air; it is better to make the entire body a respiratory organ,\nthan to construct a respiratory organ disproportioned to the magnitude\nof the body. Air-tubes diffused through every part of the body, and\nopening on its external surface, would obviously afford to every point\nof the system an easy access of air. By an expedient of this kind the\nsystem might be highly a\u00ebrated, while the respiratory apparatus would\noccupy but a comparatively small space; the function might be performed\non an extended scale, while there would be no necessity for encumbering\na minute body with a bulky organ. And this is the mode in which\nrespiration is carried on in large tribes of creatures, whose body\nis small in size and delicate in texture, and the functions of whose\neconomy are performed with energy (fig. XV.).\n\n[Illustration: Fig. XV.\n\n  The Achilles Butterfly of South America (_Papilio Achilles_),\n  showing the trache\u00e6 on the upper and under side of the wings.]\n\nBut this contrivance will not do when the animal is of large\nmagnitude; when its body is divided into numerous compartments; when\nthese compartments extend far beneath the external surface; when\nimportant organs are placed in deeply-seated cavities; and when\nthe substances that compose the organs are dense, hard, thick, and\nconvoluted. To construct air-tubes of the requisite diameter and\nlength, always open, always in a condition to permit the ingress and\negress of an adequate current of air to and from the remotest nook and\ncorner of a body such as this, would be difficult, if not impossible.\nAt all events, it is easier, in such a case, to carry the food to the\nair, than the air to the food. But, for the accomplishment of this\npurpose, what is necessary? An organ for containing food; an organ\nfor containing air; vessels to carry food to and from the receptacle\nof the aliment; vessels to carry air to and from the receptacle of\nthe air; expedients to expose a stream of food to a current of air;\nand, finally, tubes to carry out to the system the product of this\ncomplicated operation. Accordingly, a reservoir of food and a reservoir\nof air; an apparatus by which both are conveyed to their respective\nreceptacles; and an apparatus by which both are brought into contact\nsufficiently close to admit of their mutual action, are all combined\nin the lung of the animal, and in the mechanism by which its movements\nare effected. The object is accomplished, but the apparatus by which it\nis effected is as complex in structure as it is efficient in action;\nthe result simple; the means by which the result is secured, highly\ncomplicated.\n\nAnd if this be true of an inferior or organic function, it is still\nmore strikingly true of a superior or animal function. The relation is\nstill stricter between the complexity of the apparatus of sensation and\nthe range of feeling, than between the complexity of the apparatus of\nrespiration and the range of the respiratory process. The greater the\nnumber of the senses, the greater the number of the organs of sense;\nthe more accurate and varied the impressions conveyed by each, the more\ncomplex the structure of the instrument by which they are communicated;\nthe more extended the range of the intellectual operations, the larger\nthe bulk of the brain, the greater the number of its distinct parts,\nand the more exquisite their organization. From the point of the animal\nscale, at which the brain first becomes distinctly visible, up to man,\nthe basis of the organ is the same; but, as the range of its function\nextends, part after part is superadded, and the structure of each part\nbecomes progressively more and more complex. The evidence of this,\nafforded by comparative anatomy, is irresistible, and the interest\nconnected with the study of it can scarcely be exceeded.\n\n5. In the last place, structure is complex in proportion to the\nenergy of function. The greater the power with which voluntary motion\nis capable of being exerted, the higher the organization of the\napparatus by which it is performed; the more compact and dense the\nshell, the cartilage, the bone, the firmer the fibre of the muscle,\nand, in general, the greater its comparative bulk. The wing of the\neagle is as much more developed than the wing of the wren, as its\nflight is higher, and its speed swifter. The muscles which give to the\ntiger the rapidity and strength of its spring possess a more intense\norganization than those which slowly move on the tardigrade sloth. The\nstructure of the brain of man is more exquisite than that of the fish,\nas his perceptions are more acute, and capable of greater combination,\ncomprehension, and continuity.\n\nThus we see that the organization of the animal is more complex than\nthat of the plant, not from an arbitrary disposition, but from absolute\nnecessity. The few and simple functions performed by the plant require\nonly the few and simple organs with which it is provided: the numerous\nand complicated functions performed by the animal require its numerous\nand complicated organs: the plant, simple as it is in structure, is\ndestitute of no organ required by the nature of its economy; the\nanimal, complex as it is in structure, is in possession of no organ\nwhich it could dispense with: from the one, nothing is withheld which\nis needed; to the other, nothing is given which is superfluous: in the\none, there is economy without niggardliness; in the other, munificence\nwithout waste.\n\n\n\n\nCHAPTER II.\n\n  Two distinct lives combined in the animal\u2014Characters of the\n  apparatus of the organic life\u2014Characters of the apparatus of\n  the animal life\u2014Characteristic differences in the action of\n  each\u2014Progress of life\u2014Progress of death.\n\n\nOf the two sets of functions carried on by living beings, it has been\nshown, that the plant performs only one, while the animal exercises\nboth. The two lives thus in continual play in the animal differ from\neach other as much as the process of vegetation differs from that of\nthought, yet they are united so closely, and act so harmoniously,\nthat their existence as distinct states is not only not apparent to\nordinary observation, but the very discovery of the fact is of recent\ndate, and forms one among the splendid triumphs of modern physiology.\nTheir action is perfect, yet their separate identity is so distinctly\npreserved, that each has its own apparatus and its own action, which\nare not only not the same, but, in many interesting circumstances, are\nin striking contrast to each other.\n\n1. In general the organs that belong to the apparatus of the organic\nlife are single, and not symmetrical; the organs that belong to the\napparatus of the animal life are either double, or symmetrical, or\nboth. As will be shown hereafter, the heart, the lungs, the stomach,\nthe intestines, the liver, the pancreas, the spleen, the instruments\nby which the most important functions of the organic life are carried\non, are single organs. (Chap. 5.) The figure of each is more or less\nirregular, so that if a line were carried through their centre, it\nwould not divide them into two equal and precisely corresponding\nportions. On the contrary, the organs of the animal life are\nsymmetrical. The brain and the spinal cord are divisible into two\nperfectly equal parts. (Chap. 5.) The nerves which go off from these\norgans for the most part go off in pairs equal in size and similar\nin distribution. (Ibid.) The trunk, so important an instrument of\nvoluntary motion, when well formed, is divisible into two perfectly\ncorresponding portions. (Ibid.) The muscular apparatus of one half\nof the body is the exact counterpart of that of the other; while the\narms, the hands, and the lower extremities are not only double, but the\norganization of the one is precisely similar to that of its fellow.\n\n2. In general, the apparatus of the organic life is placed in the\ninterior of the body, while that of the animal life is placed on the\nexternal surface. The organic organs are the instruments by which\nlife is maintained. There is no action of any one of them that can\nbe suspended even for a short space of time without the inevitable\nextinction of life. But the animal organs are not so much instruments\nof life as means by which a certain relation is established between the\nliving being and external objects. And this difference in their office\nis the reason of the difference in their position. Existence depending\non the action of the organic organs, they are placed in the interior of\nthe body; they are fixed firmly in their situation in order that they\nmay not be disturbed by the movements of locomotion; they are enveloped\nin membranes, covered by muscles, placed under the shelter of bones,\nand every possible care is taken to secure them from accident and to\nshield them from violence. Existence not being immediately dependent\non the action of the organs of the animal life, they do not need to\nbe protected from the contact of external objects with extraordinary\ncare, but it is necessary to the performance of their functions that\nthey should be placed at the exterior of the body. And there they are\nplaced, and so placed as to afford an effectual defence to the organic\norgans. Thus the groundwork of the animal is made the bulwark of the\norganic life. The muscles, the immediate agents by which voluntary\nmotion is effected, and the bones, the fixed points and the levers by\nwhich that motion acquires the nicest precision and the most prodigious\nrapidity and power, are so disposed that, while the latter accomplish,\nin the most perfect manner, their primary and essential office in\nrelation to the muscles, they serve a secondary but scarcely less\nimportant office in relation to the internal viscera. As we advance\nin our subject, we shall see that a beautiful illustration of this is\nafforded in the structure and action of the trunk; that the trunk is\nmoveable; that it is composed of powerful muscles, and of firm and\ncompact bones; and that while its movements are effected by the action\nof the muscles which are attached to the bones, these bones enclose\na cavity, in which are placed the lungs, the heart, the great trunks\nof the venous system, the great trunks of the arterial system, and\nthe main trunk of the thoracic duct, the vessel by which the digested\naliment is carried into the blood. (Chap. 5.) Thus, by these strong and\nfirm bones, together with the thick and powerful muscles that rest upon\nthem, is formed a secure shelter for a main portion of the apparatus\nof the organic functions of respiration, circulation, and digestion.\nThe bones and muscles of the thorax, themselves performing an important\npart in the function of respiration, afford to the lungs the chief\norgan of this function, composed of tender and delicate tissues, easily\ninjured, and the slightest injury perilling life, a free and secure\nplace to act in. The fragile part of the apparatus is defended by the\nosseous portion of it, the play of the latter being equally essential\nto the function as that of the former. In like manner the tender and\ndelicate substance of the brain and spinal cord, the central seat of\nthe animal life, with which all the senses are in intimate communion,\nis protected by bones and muscles which perform important voluntary\nmovements while the organs of sense which put us in connexion with the\nexternal world, which render us susceptible of pleasure, and which\ngive us notice of the approach of objects capable of exciting pain,\nare placed where external bodies may be brought most conveniently\nand completely into contact with them; and where alone they can be\nefficient as the sentinels of the system. For this reason, with the\nexception of the sense of touch, which, though placed especially at the\nextremities of the fingers, is also diffused over the whole external\nsurface of the frame, all the senses have their several seats in the\nhead, the most elevated part of the body, of an ovoid figure, capable\nof moving independently of the rest of the fabric, and which, being\nsupported on a pivot, is enabled to describe at least two-thirds of a\ncircle.\n\nSuch is the difference in the structure and position of the apparatus\nof the two lives, but the difference in their action is still more\nstriking.\n\n1. The action of the apparatus of the organic life when sound is\nwithout consciousness; the object of the action of the apparatus of\nthe animal life is the production of consciousness. The final cause\nof the action of the apparatus of the organic life is the maintenance\nof existence; the final cause of the action of the apparatus of the\nanimal life is the production of conscious existence. What purpose\nwould be answered by connecting consciousness with the action of\nthe organic organs? Were we sensible of the organic processes; did\nwe know when the heart beats, and the lung plays, and the stomach\ndigests, and the excretory organ excretes, the consciousness could\nnot promote, but might disturb the due and orderly course of these\nprocesses. Moreover they would so occupy and engross our minds that\nwe should have little inclination or time to attend to other objects.\nBeneficently therefore are they placed equally beyond our observation\nand control. Nevertheless, when our consciousness of these processes\nmay be of service; when they are going wrong; when their too feeble or\ntoo intense action is in danger of destroying existence, the animal\nlife is made sensible of what is passing in the organic, in order that\nthe former may take beneficial cognizance of the latter, may do what\nexperience may have taught to be conducive to the restoration of the\ndiseased organ to a sound state, or avoid doing what may conduce to the\nincrease or maintenance of its morbid condition.\n\nBut while the action of the organic organs is thus kept alike from our\nview and feeling, the sole object of the action of the animal organs is\nto produce and maintain a state of varied and extended consciousness.\nWe do not know when the heart dilates to receive the vital current,\nnor when it contracts to propel it with renewed impetus through the\nsystem; nor when the blood rushes to the lung to give out its useless\nand noxious particles; nor when the air rushes to the blood to take\nup those particles, to replace them by others, and thus to purify and\nrenovate the vital fluid. Many processes of this kind are continually\ngoing on within us during every moment of our existence, but we are\nno more conscious of them than we are of the motion of the fluids in\nthe blade of grass on which we tread. On the contrary when an external\nobject produces, in a sentient nerve, that change of state which we\ndenote by the words \"an impression;\" when the sentient nerve transmits\nthis impression to the brain; when the brain is thereby brought into\nthe state of perception, the animal life is in active operation, and\npercipient or conscious existence takes place. Consciousness does not\nbelong to the organic, it _is_ the animal life.\n\n2. The functions of the organic life are performed with uninterrupted\ncontinuity; to those of the animal life rest is indispensable. The\naction of the heart is unceasing; it takes not and needs not rest.\nOn it goes, for the space of eighty or ninety years, at the rate of\na hundred thousand strokes every twenty-four hours, having at every\nstroke a great resistance to overcome, yet it continues this action for\nthis length of time without intermission. Alike incessant is the action\nof the lung, which is always receiving and always emitting air; and the\naction of the skin, which is always transpiring and always absorbing;\nand the action of the alimentary canal, which is always compensating\nthe loss which the system is always sustaining.\n\nBut of this continuity of action the organs and functions of the\nanimal life are incapable. No voluntary muscle can maintain its action\nbeyond a given time; no effort of the will can keep it in a state of\nuninterrupted contraction; relaxation must alternate with contraction;\nand even this alternate action cannot go on long without rest. No organ\nof sense can continue to receive impression after impression without\nfatigue. By protracted exertion the ear loses its sensibility to sound,\nthe eye to light, the tongue to savour, and the touch to the qualities\nof bodies about which it is conversant. The brain cannot carry on\nits intellectual operations with vigour beyond a certain period; the\ntrains of ideas with which it works become, after a time, indistinct\nand confused; nor is it capable of reacting with energy until it\nhas remained in a state of rest proportioned to the duration of its\npreceding activity.\n\nAnd this rest is sleep. Sleep is the repose of the senses, the rest of\nthe muscles, their support and sustenance. What food is to the organic,\nsleep is to the animal life. Nutrition can no more go on without\naliment, than sensation, thought, and motion without sleep.\n\nBut it is the animal life only that sleeps: death would be the\nconsequence of the momentary slumber of the organic. If, when the brain\nbetook itself to repose, the engine that moves the blood ceased to\nsupply it with its vital fluid, never again would it awake. The animal\nlife is active only during a portion of its existence; the activity of\nthe organic life is never for a moment suspended; and in order to endow\nits organs with the power of continuing this uninterrupted action,\nthey are rendered incapable of fatigue: fatigue, on the contrary, is\ninseparable from the action of the organs of the animal life; fatigue\nimposes the necessity of rest, rest is sleep, and sleep is renovation.\n\n3. Between all the functions of the organic life there is a close\nrelation and dependence. Without the circulation there can be no\nsecretion; without secretion, no digestion; without digestion, no\nnutrition; without nutrition, no new supply of circulating matter,\nand so through the entire circle. But the functions of the animal\nlife are not thus dependent on each other. One of the circle may be\ndisordered without much disturbance of the rest; and one may cease\naltogether, while another continues in vigorous action. Sensation may\nbe lost, while motion continues; and the muscle may contract though it\ncannot feel. One organ of sense may sleep while the rest are awake.\nOne intellectual faculty may be in operation while others slumber. The\nmuscle of volition may act, while there is no consciousness of will.\nEven the organs of the voice and of progression may perform their\noffice while the sensorium is deeply locked in sleep.\n\n4. The two lives are born at different periods, and the one is in\nactive operation before the other is even in existence. The first\naction observable in the embryo is a minute pulsating point. It is the\nyoung heart propelling its infant stream. Before brain, or nerve, or\nmuscle can be distinguished, the heart is in existence and in action;\nthat is, the apparatus of the organic function of the circulation is\nbuilt up and is in operation before there is any trace of an animal\norgan. Arteries and veins circulate blood, capillary vessels receive\nthe vital fluid, and out of it form brain and muscle, the organs of the\nanimal, no less than the various substances that compose the organs of\nthe organic life. The organic is not only anterior to the animal life,\nbut it is by the action of the organic that existence is given to the\nanimal life. The organic life is born at the first moment of existence;\nthe animal life not until a period comparatively distant; the epoch\nemphatically called the period of birth, namely, the period when\nthe new being is detached from its mother; when it first comes into\ncontact with external objects; when it carries on all the functions\nof its economy by its own organs, and consequently enjoys independent\nexistence.\n\n5. The functions of the organic life are perfect at once. The heart\ncontracts as well, the arteries secrete as well, the respiratory\norgans work as well the first moment they begin to act as at any\nsubsequent period. They require no teaching from experience, and they\nprofit nothing from its lessons. On the contrary, the operations\nof the brain, and the actions of the voluntary muscles, feeble and\nuncertain at first, acquire strength by slow degrees, and attain\ntheir ultimate perfection only at the adult age. How indistinct\nand confused the first sensations of the infant! Before it acquire\naccuracy, precision, and truth, how immense the labour spent upon\nperception! Sensations are succeeded by ideas; sensations and ideas\ncoalesce with sensations and ideas; combinations thus formed suggest\nother combinations previously formed, and these a third, and the third\na fourth, and so is constituted a continuous train of thought. But\nthe infantile associations between sensation and sensation, between\nidea and idea, and between sensations and ideas, are, to a certain\nextent, incorrect, and to a still greater extent inadequate; and the\nmisconception necessarily resulting from this early imperfection in the\nintellectual operations is capable of correction only by subsequent and\nmore extended impressions. During its making hours, a large portion of\nthe time of the infant is spent in receiving impressions which come\nto it every instant from all directions, and which it stores up in\nits little treasury; but a large portion is also consumed in the far\nmore serious and difficult business of discrimination and correction.\nCould any man, after having attained the age of manhood, reverse the\norder of the course through which he has passed; could he, with the\npower of observation, together with the experience that belong to\nmanhood, retrace with perfect exactness every step of his sentient\nexistence, from the age of forty to the moment that the air first came\ninto contact with his body at the moment of his leaving his maternal\ndwelling, among the truths he would learn, the most interesting, if\nnot the most surprising, would be those which relate to the manner in\nwhich he dealt with his earliest impressions; with the mode in which\nhe combined them, recalled them, laid them by for future use; made his\nfirst general deduction; observed what subsequent experience taught to\nbe conformable, and what not conformable, to this general inference;\nhis emotions on detecting his first errors, and his contrasted feelings\non discovering those comprehensive truths, the certainty of which\nbecame confirmed by every subsequent impression. Thus to live backwards\nwould be, in fact, to go through the analysis of the intellectual\ncombinations, and, consequently, to obtain a perfect insight into the\nconstitution of the mind; and among the curious results which would\nthen become manifest, perhaps few would appear more surprising than the\ntrue action of the senses. The eye, when first impressed by light, does\nnot perceive the objects that reflect it; the ear, when first impressed\nby sound, does not distinguish the sonorous body. When the operation\nfor cataract has been successfully performed in a person born blind,\nthe eye immediately becomes sensible to light, but the impression of\nlight does not immediately give information relative to the properties\nof bodies. It is gradually, not instantaneously; it is even by slow\ndegrees that luminous objects are discerned with distinctness and\naccuracy. To see, to hear, to smell, to taste, to touch, are processes\nwhich appear to be performed instantaneously, and which actually are\nperformed with astonishing rapidity in a person who observes them\nin himself; but they were not always performed thus rapidly: they\nare processes acquired, businesses learnt; processes and businesses\nacquired and learnt, not without the cost of many efforts and much\nlabour. But the senses afford merely the materials for the intellectual\noperations of memory, combination, comparison, discrimination,\ninduction, operations the progress of which is so slow, that they\nacquire precision, energy, and comprehensiveness only after the culture\nof years.\n\nAnd the same is true of the muscles of volition. How many efforts are\nmade before the power of distinct articulation is acquired! how many\nbefore the infant can stand! how many before the child can walk! The\norganic life is born perfect; the animal life becomes perfect only by\nservitude, and the aptitude which service gives.\n\n6. The organic life may exist after the animal life has perished. The\nanimal life is extinguished when sensation is abolished, and voluntary\nmotion can be performed no more. But disease may abolish sensation and\ndestroy the power of voluntary motion, while circulation, respiration,\nsecretion, excretion, in a word, the entire circle of the organic\nfunctions continues to be performed. In a single instant apoplexy may\nreduce to drivelling fatuity the most exalted intellect, and render\npowerless and motionless muscles of gigantic strength; while the action\nof the heart and the involuntary contractions of the muscles may not\nonly not be weakened, but may act with preternatural energy. In a\nsingle instant, apoplexy may even completely extinguish the animal\nlife, and yet the organic may go on for hours, days, and even weeks;\nwhile catalepsy, perhaps the most singular disease to which the human\nframe is subject, may wholly abolish sensation and volition, while\nit may impart to the voluntary muscles the power of contracting with\nsuch unnatural energy and continuity, that the head, the trunk, the\nlimbs may become immoveably fixed in whatever attitude they happen\nto be at the moment the paroxysm comes on. In this extraordinary\ncondition of the nervous system, however long the paroxysm last, and\nhowever complete the abolition of consciousness, the heart continues\nto beat, and the pulse to throb, and the lungs to respire, and all the\norganic organs to perform their ordinary functions. Dr. Jebb gives the\nfollowing description of the condition of a young lady who was the\nsubject of this curious malady.\n\n\"My patient was seized with an attack just as I was announced. At that\nmoment she was employed in netting; she was in the act of passing\nthe needle through the mesh; in that position she became immoveably\nrigid, exhibiting, in a pleasing form, a figure of death-like sleep,\nbeyond the power of art to imitate, or the imagination to conceive.\nHer forehead was serene, her features perfectly composed. The paleness\nof her colour, and her breathing, which at a distance was scarcely\nperceptible, operated in rendering the similitude to marble more exact\nand striking. The position of her fingers, hands, and arms was altered\nwith difficulty, but preserved every form of flexure they acquired:\nnor were the muscles of the neck exempted from this law, her head\nmaintaining every situation in which the hand could place it, as firmly\nas her limbs.\"\n\nIn this condition of the system the senses were in a state of profound\nsleep; the voluntary muscles, on the contrary, were in a state of\nviolent action; but this action not being excited by volition, nor\nunder its control, the patient remained as motionless as she was\ninsensible. The brain was in a state of temporary death; the muscle\nin a state of intense life. And the converse may happen: the muscle\nmay die, while the brain lives; contractility may be destroyed, while\nsensibility is perfect; the power of motion may be lost, while that of\nsensation may remain unaffected. A case is on record, which affords\nan illustration of this condition of the system. A woman had been for\nsome time confined to her bed, labouring under severe indisposition.\nOn a sudden she was deprived of the power of moving a single muscle of\nthe body; she attempted to speak, but she had no power to articulate;\nshe endeavoured to stretch out her hand, but her muscles refused to\nobey the commands of her will, yet her consciousness was perfect, and\nshe retained the complete possession of her intellectual faculties.\nShe perceived that her attendants thought her dead, and was conscious\nof the performance upon her own person of the services usually paid to\nthe dead; she was laid out, her toes were bound together, her chin was\ntied up; she heard the arrangements for her funeral discussed, and yet\nshe was unable to make the slightest sign that she was still in the\npossession of sense, feeling, and life.\n\nIn one form of disease, then, the animal life, both the sensitive and\nthe motive portions of it, may perish; and in another form of disease,\neither the one or the other part of it may be suspended, while the\norganic life continues in full operation: it follows that the two\nlives, blended as they are, are distinct, since the one is capable of\nperishing without immediately and inevitably involving the destruction\nof the other.\n\n7. And, finally, as the organic life is the first born, so it is the\nlast to die; while the animal life, as it is the latest born, and\nthe last to attain its full development, so it is the earliest to\ndecline and the first to perish. In the process of natural death, the\nextinction of the animal is always anterior to that of the organic\nlife. Real death is a later, and sometimes a much later event than\napparent death. An animal appears to be dead when, together with the\nabolition of sensation and the loss of voluntary motion, respiration,\ncirculation, and the rest of the organic functions can no longer be\ndistinguished; but these functions go on some time after they have\nceased to afford external indications of their action. In man, and the\nwarmblooded animals in general, suspension or submersion extinguishes\nthe animal life, at the latest, within the space of four minutes from\nthe time that the atmospheric air is completely excluded from the\nlung; but did the organic functions also cease at the same period, it\nwould be impossible to restore an animal to life after apparent death\nfrom drowning and the like. But however complete and protracted the\nabolition of the animal functions, re-animation is always possible as\nlong as the organic organs are capable of being restored to their usual\nvigour. The cessation of the animal life is but the first stage of\ndeath, from which recovery is possible; death is complete only when the\norganic together with the animal functions have wholly ceased, and are\nincapable of being re-established.\n\nIn man, the process of death is seldom altogether natural. It is\ngenerally rendered premature by the operation of circumstances which\ndestroy life otherwise than by that progressive and slow decay which is\nthe inevitable result of the action of organized structure. Death, when\nnatural, is the last event of an extended series, of which the first\nthat is appreciable is a change in the animal life and in the noblest\nportion of that life. The higher faculties fail in the reverse order of\ntheir development; the retrogression is the inverse of the progression,\nand the noblest creature, in returning to the state of non-existence,\nretraces step by step each successive stage by which it reached the\nsummit of life.\n\nIn the advancing series, the animal is superadded to the organic\nlife; sensation, the lowest faculty of the animal life, precedes\nratiocination, the highest. The senses called into play at the moment\nof birth soon acquire the utmost perfection of which they are capable;\nbut the intellectual faculties, later developed, are still later\nperfected, and the highest the latest.\n\nIn the descending series, the animal life fails before the organic, and\nits nobler powers decay sooner and more rapidly than the subordinate.\nFirst of all, the impressions which the organs of sense convey to\nthe brain become less numerous and distinct, and consequently the\nmaterial on which the mind operates is less abundant and perfect; but\nat the same time, the power of working vigorously with the material it\npossesses more than proportionally diminishes. Memory fails; analogous\nphenomena are less readily and less completely recalled by the presence\nof those which should suggest the entire train; the connecting links\nare dimly seen or wholly lost; the train itself is less vivid and less\ncoherent; train succeeds train with preternatural slowness, and the\nconsequence of these growing imperfections is that, at last, induction\nbecomes unsound just as it was in early youth; and for the same\nreason, namely, because there is not in the mental view an adequate\nrange of individual phenomena; the only difference being that the\nrange comprehended in the view of the old man is too narrow, because\nthat which he had learnt he has forgotten; while in the youth it is\ntoo narrow, because that which it is necessary to learn has not been\nacquired.\n\nAnd with the diminution of intellectual power the senses continue\nprogressively to fail: the eye grows more dim, the ear more dull, the\nsense of smell less delicate, the sense of touch less acute, while\nthe sense of taste immediately subservient to the organic function of\nnutrition is the last to diminish in intensity and correctness, and\nwholly fails but with the extinction of the life it serves.\n\nBut the senses are not the only servants of the brain; the voluntary\nmuscles are so equally; but these ministers to the master-power, no\nlonger kept in active service, the former no longer employed to convey\nnew, varied, and vivid impressions, the latter no longer employed\nto execute the commands of new, varied, and intense desires, become\nsuccessively feebler, slower, and more uncertain in their action.\nThe hand trembles, the step totters, and every movement is tardy and\nunsteady. And thus, by the loss of one intellectual faculty after\nanother, by the obliteration of sense after sense, by the progressive\nfailure of the power of voluntary motion; in a word, by the declining\nenergy and the ultimate extinction of the animal life, man, from the\nstate of maturity, passes a second time through the stage of childhood\nback to that of infancy; lapses even into the condition of the embryo:\nwhat the f\u0153tus was, the man of extreme old age is: when he began to\nexist, he possessed only organic life; and before he is ripe for the\ntomb, he returns to the condition of the plant.\n\nAnd even this merely organic existence cannot be long maintained. Slow\nmay be the waste of the organic organs; but they do waste, and that\nwaste is not repaired, and consequently their functions languish, and\nno amount of stimulus is capable of invigorating their failing action.\nThe arteries are rigid and cannot nourish; the veins are relaxed and\ncannot carry on the mass of blood that oppresses them; the lungs,\npartly choked up by the deposition of adventitious matter, and partly\nincapable of expanding and collapsing by reason of the feeble action\nof the respiratory apparatus, imperfectly a\u00ebrate the small quantity\nof blood that flows through them; the heart, deprived of its wonted\nnutriment and stimulus, is unable to contract with the energy requisite\nto propel the vital current; the various organs, no longer supplied\nwith the quantity and quality of material necessary for carrying on\ntheir respective processes, cease to act; the machinery stops, and this\nis death.\n\nAnd now the processes of life at an end, the body falls within the\ndominion of the powers which preside universally over matter; the tie\nthat linked all its parts together, holding them in union and keeping\nthem in action, in direct opposition to those powers dissolved, it\nfeels and obeys the new attractions to which it has become subject;\nparticle after particle that stood in beautiful order fall from their\nplace; the wonderful structures they composed melt away; the very\nsubstances of which those structures were built up are resolved into\ntheir primitive elements; these elements, set at liberty, enter into\nnew combinations, and become constituent parts of new beings; those new\nbeings in their turn perish; from their death springs life, and so the\nchanges go on in an everlasting circle.\n\nAs far as relates to the organized structures in which life has its\nseat, and to the operations of life dependent on those structures,\nsuch is its history; a history not merely curious, but abounding with\npractical suggestions of the last importance. The usefulness of a\nfamiliar acquaintance with the phenomena which have now been elucidated\nwill be apparent at every step as we proceed.\n\n\n\n\nCHAPTER III.\n\n  Ultimate object of organization and life\u2014Sources of\n  pleasure\u2014Special provision by which the organic organs\n  influence consciousness and afford pleasure\u2014Point at which\n  the organic organs cease to affect consciousness, and\n  why\u2014The animal appetites: the senses: the intellectual\n  faculties: the selfish and sympathetic affections: the\n  moral faculty\u2014Pleasure the direct, the ordinary, and the\n  gratuitous result of the action of the organs\u2014Pleasure\n  conducive to the development of the organs, and to\n  the continuance of their action\u2014Progress of human\n  knowledge\u2014Progress of human happiness.\n\n\nThe object of structure is the production of function. Of the two\nfunctions combined in the living animal, one is wholly subservient\nto the other. To build up the apparatus of the animal life, and to\nmaintain it in a condition fit for performing its functions, is the\nsole object of the existence of the organic life. What then is the\nobject of the animal life? That object, whatever it be, must be the\nultimate end of organization, and of all the actions of which it is the\nseat and the instrument.\n\nTwo functions, sensation and voluntary motion, are combined in the\nanimal life. Of these two functions, the latter is subservient to the\nformer: voluntary motion is the servant of sensation, and exists only\nto obey its commands.\n\nIs sensation, then, the ultimate object of organization? Simple\nsensation cannot be an ultimate object, because it is invariably\nattended with an ultimate result; for sensation is either pleasurable\nor painful. Every sensation terminates in a pleasure or a pain.\nPleasure or pain, the last event in the series, must then be the final\nend.\n\nIs the production of pain the ultimate object of organization? That\ncannot be, for the production of pain is the indirect, not the\ndirect,\u2014the extraordinary, not the ordinary, result of the actions\nof life. It follows that pleasure must be the ultimate object, for\nthere is no other of which it is possible to conceive. The end of\norganic existence is animal existence; the end of animal existence\nis sentient existence; the end of sentient existence is pleasurable\nexistence; the end of life therefore is enjoyment. Life commences with\nthe organic processes; to the organic are superadded the animal; the\nanimal processes terminate in sensation; sensation ends in enjoyment;\nit follows, that enjoyment is the final end. For this every organ is\nconstructed; to this every action of every organ is subservient; in\nthis every action ultimately terminates.\n\nAnd without a single exception in the entire range of the sentient\ncreation, the higher the organized structure the greater the enjoyment,\nmediately or immediately, to which it is subservient. From its most\nsimple to its most complex state, every successive addition to\nstructure, by which function is rendered more elevated and perfect,\nproportionally increases the exquisiteness of the pleasure to which the\nfunction ministers, and in which it terminates.\n\nPleasure is the result of the action of living organs, whether\norganic or animal; pleasure is the direct, the ordinary, and the\ngratuitous result of the action of both sets of organs; the pleasure\nresulting from the action of the organs is conducive to their complete\ndevelopment, and thereby to the increase of their capacity for\naffording enjoyment; the pleasure resulting from the action of the\norgans, and conducive to their development, is equally conducive to the\nperpetuation of their action, and consequently to the maintenance of\nlife; it follows not only that enjoyment is the end of life, but that\nit is the means by which life is prolonged. Of the truth of each of\nthese propositions, it will be interesting to contemplate the plenitude\nof the proof.\n\n1. In the first place, pleasure is the result of the action of the\norganic organs. It has indeed been shown that the very character by\nwhich the action of these organs is distinguished is that they are\nunattended with consciousness. Nevertheless, by a special provision,\nconsciousness is indirectly connected with the processes of this\nclass, limited in extent indeed, and uniformly terminating at a\ncertain point; but the extent and the limitation alike conducing to\nthe pleasurableness of its nature. And this is an adjustment in the\nconstitution of our frame which is well deserving of attention.\n\nOrganic processes are dependent on a peculiar influence derived from\nthat portion of the nervous system distinguished by the term organic.\nThe organic nerves, distributed to the organic organs, take their\norigin and have their chief seat in the cavities that contain the main\ninstruments of the organic life, namely, the chest and abdomen (see\nchap. v.). As will be fully shown hereafter, these nerves encompass\nthe great trunks of the blood-vessels that convey arterial blood\nto the organic organs. In all its ramifications through an organic\norgan, an arterial vessel is accompanied by its organic nerve; so that\nwherever the capillary arterial branch goes, secreting or nourishing,\nthere goes, inseparably united with it, an organic nerve, exciting and\ngoverning.\n\nAmong the peculiarities of this portion of the nervous system, one\nof the most remarkable is, that it is wholly destitute of feeling.\nSensibility is inseparably associated with the idea commonly formed of\na nerve. But the nervous system consists of two portions, one presiding\nover sensation and voluntary motion, hence called the sentient and\nthe motive portions; the other destitute of sensation, but presiding\nover the organic processes, hence called the organic portion. If the\ncommunication between the organic organ and the organic nerve be\ninterrupted, the function of the organ, whatever it be, is arrested.\nWithout its organic nerves, the stomach cannot secrete gastric juice;\nthe consequence is, that the aliment is undigested. Without its organic\nnerves, the liver cannot secrete bile, the consequence is, that the\nnutritive part of the aliment is incapable of being separated from its\nexcrementitious portion. The organic organ receives from its organic\nnerve an influence, without which it cannot perform its function;\nbut the nerve belonging to this class neither feels nor communicates\nfeeling, and hence it imparts no consciousness of the operation of any\nprocess dependent upon it. Yet there is not one of these processes that\ndoes not exert a most important influence over consciousness. How? By a\nspecial provision, as curious in its nature as it is important in its\nresult.\n\nBranches of sentient nerves are transmitted from the animal to the\norganic system, and from the organic to the animal; and an intimate\ncommunication is established between the two classes. The inspection\nof fig. XVI. will illustrate the mode in which this communication is\neffected. A B represents a portion of the spinal cord (one of the\ncentral masses of the sentient system), covered with its membranes. The\npart here represented is a front view of that portion of the spinal\ncord which belongs to the back, and which is technically called the\ndorsal portion.\n\n[Illustration: Fig. XVI.]\n\n1, 2, 3, 4, 5, 6, 7, 8, 9, the second, &c. ribs with the corresponding\ndorsal (sentient) nerves, _a_, _b_, _c_, _d_, _e_, _f_, _g_, _h_, going\nout to supply their respective organs with sensation.\n\nC D E, a portion of the main trunk of the organic (non-sentient) nerve,\ncommonly called the Great Sympathetic.\n\nF G H, the membrane of the spinal cord cut open and exposing I K, the\nspinal cord itself, L, the anterior branch of one of the dorsal nerves,\narising from the anterior surface of the spinal cord by several bundles\nof fibres.\n\nM, the posterior branch of the same nerve, arising in like manner from\nthe posterior surface of the spinal cord by several branches of fibres.\n\nThe anterior and posterior branches uniting to form one trunk N.\n\nTwo branches, P Q, sent off from the spinal (sentient) trunk to unite\nwith the organic (non-sentient) trunk.\n\nR S T U V W, other branches of the sentient, connected with the\nbranches of the non-sentient nervous trunks in the same mode.\n\nX Y, the main trunk of the sympathetic (non-sentient) nerve cut across\nand turned aside, in order that the parts beneath it (P N) may be more\ndistinctly seen.\n\nFrom this description, it is apparent that each sentient nerve,\nbefore it goes out to the animal organs, to which it is destined to\ncommunicate sensation, sends off two branches to the organic or the\nnon-sentient. These sentient nerves mix and mingle with the insensible\nnerves; accompany them in their course to the organic organs, and\nramify with them throughout their substance. It is manifest, then,\nthat sentient nerves, that nerves not necessary to the organic\nprocesses, having, as far as is known, nothing whatever to do with\nthose processes, enter as constituent parts into the composition of the\norganic organs. What is the result? That organic organs are rendered\nsentient; that organic processes, in their own nature insensible,\nbecome capable of affecting consciousness. What follows? What is the\nconsciousness excited? Not a consciousness of the organic process.\nOf that we still remain wholly insensible. Not simple sensation. The\nresult uniformly produced, as long as the state of the system is that\nof health, is pleasurable consciousness. The heart sends out to the\norgans its vital current. Each organ, abstracting from the stream the\nparticles it needs, converts them into the peculiar fluid or solid\nit is its office to form. The stomach, from the arterial streamlets\ncirculating through it, secretes gastric juice; the liver, from the\nvenous streamlets circulating through it, secretes bile. When these\ndigestive organs have duly prepared their respective fluids, they\nemploy them in the elaboration of the aliment. We are not conscious\nof this elaboration, though it go on within us every moment; but is\nconsciousness not affected by the process? Most materially. Why?\nBecause sentient mingle with organic nerves; because the sentient\nnerves are impressed by the actions of the organic organs. And how\nimpressed? As long as the actions of the organic organs are sound,\nthat is, as long as their processes are duly performed, the impression\ncommunicated to the sentient nerves is in its nature agreeable; is,\nin fact, THE PLEASURABLE CONSCIOUSNESS WHICH CONSTITUTES THE FEELING\nOF HEALTH. The state of health is nothing but the result of the\ndue performance of the organic organs: it follows that the feeling\nof health, the feeling which is ranked by every one among the most\npleasurable of existence, is the result of the action of organs of\nwhose direct operations we are unconscious. But the pleasurable\nconsciousness thus indirectly excited is really the consequence of a\nspecial provision, established for the express purpose of producing\npleasure. Processes, in their own nature insensible, are rendered\nsentient expressly for this purpose, that, over and above the special\nobject they serve, they may afford enjoyment. In this case, the\nproduction of pleasure is not only altogether gratuitous, not only\ncommunicated for its own sake, not only rested in as an ultimate\nobject, but it is made to commence at the very confines of life; it is\ninterwoven with the thread of existence: it is secured in and by the\nactions that build up and that support the very framework, the material\ninstrument of our being.\n\nBut if the communication of sensibility to processes in their own\nnature incapable of exciting feeling, for the purpose of converting\nthem into sources of pleasurable consciousness, indicate an express\nprovision for the production of enjoyment, that provision is no less\nexemplified in the point at which this superadded sensibility is made\nto cease.\n\nSome of the consequences of a direct communication of consciousness\nto an organic process have been already adverted to. Had the eye,\nbesides transmitting rays of light to the optic nerve, been rendered\nsensible of the successive passage of each ray through its substance,\nthe impression excited by luminous bodies, which is indispensable to\nvision, the ultimate object of the instrument, if not wholly lost,\nmust necessarily have become obscure, in direct proportion to the\nacuteness of this sensibility. The hand of the musician could scarcely\nhave executed its varied and rapid movements upon his instrument, had\nhis mind been occupied at one and the same instant with the process\nof muscular contraction in the finger, and the idea of music in the\nbrain. Had the communication of such a twofold consciousness been\npossible, in no respect would it have been beneficial, in many it would\nhave been highly pernicious; and the least of the evils resulting\nfrom it would have been, that the inferior would have interrupted the\nsuperior faculty, and the means deteriorated the end. But in some\ncases the evil would have been of a much more serious nature. Had we\nbeen rendered sensible of the flow of the vital current through the\nengine that propels it; were the distension of the delicate valves that\ndirect the current ever present to our view; by some inward feeling\nwere we reminded, minute by minute, of the progress of the aliment\nthrough the digestive apparatus, and were the mysterious operations\nof the organic nerves palpable to sight, the terror of the maniac,\nwho conceived that his body was composed of unannealed glass, would\nbe the ordinary feeling of life. Every movement would be a matter of\nanxious deliberation; and the approach of every body to our own would\nfill us with dismay. But adjusted as our consciousness actually is,\ninvariably the point at which the organic process begins is that at\nwhich sensation ends. Had sensation been extended beyond this point, it\nwould have been productive of pain: at this point it uniformly stops.\nNevertheless, by the indirect connexion of sensation with the organic\nprocesses, a vast amount of pleasure might be created: a special\napparatus is constructed for the express purpose of establishing the\ncommunication. There is thus the twofold proof, the positive and the\nnegative, the evidence arising as well from what they do, as from\nwhat they abstain from doing, that the organic processes are, and are\nintended to be, sources of enjoyment.\n\nBut the production of pleasure, commencing at this the lowest point\nof conscious existence, increases with the progressive advancement of\norganization and function.\n\nThe appetite for food, and the voluntary actions dependent upon it,\nmay be considered as the first advancement beyond a process purely\norganic. The function by which new matter is introduced into the\nsystem and converted into nutriment, is partly an animal and partly an\norganic operation. The animal part of it consists of the sensations of\nhunger and thirst, by which we are taught when the wants of the system\nrequire a fresh supply of aliment, together with the voluntary actions\nby which the aliment is introduced into the system. The organic part\nof the function consists of the changes which the aliment undergoes\nafter its introduction into the system, by which it is converted into\nnutriment. Sensations always of a pleasurable nature arise indirectly\nin the manner already explained, from the due performance of the\norganic part of the function; but pleasure is also directly produced by\nthe performance of the animal part of it. Wholesome food is grateful;\nthe satisfaction of the appetite for food is pleasurable. Food is\nnecessary to the support of life; but it is not indispensable to the\nmaintenance of life that food should be agreeable. Appetite there\nmust be, that food may be eaten; but the act of eating might have\nbeen secured without connecting it with pleasure. Pleasure, however,\nis connected with it, first directly, by the gratefulness of food,\nand secondly indirectly, by the due digestion of the food. And the\nannexation of pleasure in this twofold mode to the performance of the\nfunction of nutrition is another case of the gratuitous bestowment of\npleasure; another instance in which pleasure is communicated for its\nown sake, and rested in as an ultimate object. Pleasures of this class\nare sometimes called low; they are comparatively low; but they are not\nthe less pleasures, because they are exceeded in value by pleasures of\na nobler nature. Man may regard them with comparative indifference,\nbecause he is endowed with faculties which afford him gratifications\nsuperior in kind and larger in amount; but it is no mark of wisdom to\ndespise and neglect even these: for they are annexed to the exercise\nof a function which is the first to exalt us above a merely organic\nexistence; they are the first pleasures of which, considered merely as\nsentient creatures, we are susceptible; they amount in the aggregate to\nan immense sum; and they mark the depth in our nature in which are laid\nthe fountains of enjoyment.\n\nOrgans of sense, intellectual faculties, social affections, moral\npowers, are superadded endowments of a successively higher order:\nat the same time, they are the instruments of enjoyment of a nature\nprogressively more and more exquisite.\n\nAn organ of sense is an instrument composed of a peculiar arrangement\nof organized matter, by which it is adapted to receive from specific\nagents definite impressions. Between the agent that produces and the\norgan that receives the impression, the adaptation is such, that the\nresult of their mutual action is, in the first place, the production of\nsensation, and, in the second place, the production of pleasure. The\npleasure is as much the result as the sensation. This is true of the\neye in seeing, the ear in hearing, the hand in touching, the organ of\nsmell in smelling, and the tongue in tasting. Pleasure is linked with\nthe sense; but there might have been the sense without the pleasure.\nA slight difference in the construction of the organ, or in the\nintensity of the agent, would not merely have changed, it would even\nhave reversed the result; would have rendered the habitual condition of\nthe eye, the ear, the skin, not such as it now is in health, but such\nas it is in the state of inflammation. But the adjustment is such as\nhabitually to secure that condition of the system in which every action\nthat excites sensation produces pleasure as its ordinary concomitant;\nand the amount of enjoyment which is thus secured to every man, and\nwhich every man without exception actually experiences in the ordinary\ncourse of an ordinary life, it would be beyond his power to estimate\nwere he always sensible of the boon; but the calculation is altogether\nimpossible, when, as is generally the case, he merely enjoys without\never thinking of the provisions which enable him to do so.\n\nBut if the pleasures that arise from the ordinary operations of sense\nform, in the aggregate, an incalculable sum, how great is the accession\nbrought to this stock by the endowments next in order in the ascending\nscale, namely, the intellectual faculties!\n\nThere is one effect resulting from the operation of the intellectual\nfaculties on the senses that deserves particular attention. The higher\nfaculties elevate the subordinate in such a manner as to make them\naltogether new endowments. In illustration of this, it will suffice\nto notice the change wrought, as if in the very nature of sensation,\nthe moment it becomes combined with an intellectual operation, as\nexemplified in the difference between the intellectual conception of\nbeauty, and the mere perception of sense. The grouping of the hills\nthat bound that magnificent valley which I behold at this moment spread\nout before my view; the shadow of the trees at the base of some of\nthem, stretching its deep and varied outline up the sides of others;\nthe glancing light now brightening a hundred different hues of green\non the broad meadows, and now dancing on the upland fallows; the\never-moving, ever-changing clouds; the scented air; the song of birds;\nthe still more touching music which the breeze awakens in the scarcely\ntrembling branches of those pine trees,\u2014the elements of which this\nscene is composed, the mere objects of sense, the sun, the sky, the\nair, the hills, the woods, and the sounds poured out from them, impress\nthe senses of the animals that graze in the midst of them; but on their\nsenses they fall dull and without effect, exciting no perception of\ntheir loveliness, and giving no taste of the pleasures they are capable\nof affording. Nor even in the human being, whose intellectual faculties\nhave been uncultivated, do they awaken either emotions or ideas; the\nclown sees them, hears them, feels them no more than the herds he\ntends: yet in him whose mind has been cultivated and unfolded, how\nnumerous and varied the impressions, how manifold the combinations, how\nexquisite the pleasures produced by objects such as these!\n\nAnd from the more purely intellectual operations, from memory,\ncomparison, analysis, combination, classification, induction, how\nstill nobler the pleasure! Not to speak of the happiness of him who,\nby his study of natural phenomena, at length arrived at the stupendous\ndiscovery that the earth and all the stars of the firmament move, and\nthat the feather falls to the ground, by the operation of one and the\nsame physical law; nor of the happiness of him who sent his kite into\nthe cloud, and brought down from its quiet bed the lightning which\nhe suspected was slumbering there; nor of the happiness of him who\nconcentrated, directed, and controlled that mighty power which has\nenabled the feeble hand of man to accomplish works greater than have\nbeen feigned of fabled giant; which has annihilated distance; created,\nby economizing time; changed in the short space in which it has been in\noperation the surface of the habitable globe; and is destined to work\nupon it more and greater changes than have been effected by all other\ncauses combined; nor of the happiness of him who devoted a longer life\nwith equal success to a nobler labour, that of REARING THE FABRIC OF\nFELICITY BY THE HAND OF REASON AND OF LAW. The intellectual pleasures\nof such men as Newton, Franklin, Watt, and Bentham, can be _equalled_\nonly by those who possess equal intellectual power, and who put forth\nequal intellectual energy: to be greatly happy as they were, it were\nnecessary to be as highly endowed; but to be happy, it is not necessary\nto be so endowed. In the ordinary intellectual operations of ordinary\nmen, in their ordinary occupations, there is happiness. Every human\nbeing whose moments have passed with winged speed, whose day has been\nshort, whose year is gone almost as soon as it seemed commenced, has\nderived from the exercise of his intellectual faculties pleasures\ncountless in number and inestimable in value.\n\nBut the sympathetic pleasures, out of which grow the social, are of\na still higher order even than the intellectual. The pleasures that\nresult from the action of the organic organs, from the exercise of the\nseveral senses, and from the operation of the intellectual faculties,\nlike the sensations in which they arise, belong exclusively to the\nindividual being that experiences them, and cannot be communicated\nto another. Similar sensations and pleasures may be felt by beings\nsimilarly constituted; but the actual sensations and pleasures afforded\nby the exercise of a person's own organs and faculties are no more\ncapable of becoming another's than his existence. These, then, are\nstrictly the selfish pleasures; and the provision that has been made\nfor securing them has been shown.\n\nBut there are pleasures of another class, pleasures having no relation\nwhatever to a person's own sensation or happiness; pleasures springing\nfrom the perception of the enjoyment of others. The sight of pleasure\nnot its own affects the human heart, provided its state of feeling be\nnatural and sound, just as it would be affected were it its own. Not\nmore real is the pleasure arising from the gratification of appetite,\nthe exercise of sense, and the operation of intellect, than that\narising from the consciousness that another sentient being is happy.\nPleasures of this class are called sympathetic, in contradistinction to\nthose of the former class, which are termed selfish.\n\nThere are then two principles in continual operation in the human\nbeing, the selfish and the sympathetic. The selfish is productive of\npleasure of a certain kind; the sympathetic is productive of pleasure\nof another kind. The selfish is primary and essential; the sympathetic,\narising out of the selfish, is superadded to it. And so precisely\nwhat the animal life is to the organic, the sympathetic principle is\nto the selfish; and just what the organic life gains by its union\nwith the animal, the mental constitution gains by the addition of\nthe sympathetic to the selfish affection. The analogy between the\ncombination in both cases is in every respect complete. As the organic\nlife produces and sustains the animal, so the sympathetic principle\nis produced and sustained by the selfish. As the organic life is\nconservative of the entire organization of the body, so the selfish\nprinciple is conservative of the entire being. As the animal life is\nsuperadded to the organic, extending, exalting, and perfecting it,\nso the sympathetic principle is superadded to the selfish, equally\nextending, exalting, and perfecting it. The animal life is nobler than\nthe organic, whence the organic is subservient to the animal; but there\nis not only no opposition, hostility, or antagonism between them, but\nthe strictest possible connexion, dependence, and subservience. The\nsympathetic principle is nobler than the selfish, whence the selfish is\nsubservient to the sympathetic; but there is not only no opposition,\nhostility, or antagonism between them, but the strictest possible\nconnexion, dependence, and subservience. Whatever is conducive to the\nperfection of the organic, is equally conducive to the perfection of\nthe animal life; and whatever is conducive to the attainment of the\ntrue end of the selfish is equally conducive to the attainment of the\ntrue end of the sympathetic principle. The perfection of the animal\nlife cannot be promoted at the expense of the organic, nor that of the\norganic at the expense of the animal; neither can the ultimate end of\nthe selfish principle be secured by the sacrifice of the sympathetic,\nnor that of the sympathetic by the sacrifice of the selfish. Any\nattempt to exalt the animal life beyond what is compatible with the\nhealthy state of the organic, instead of accomplishing that end, only\nproduces bodily disease. Any attempt to extend the selfish principle\nbeyond what is compatible with the perfection of the sympathetic,\nor the sympathetic beyond what is compatible with the perfection of\nthe selfish, instead of accomplishing the end in view, only produces\nmental disease. Opposing and jarring actions, antagonizing and mutually\ndestructive powers, are combined in no other work of nature; and it\nwould be wonderful indeed were the only instance of it found in man,\nthe noblest of her works, and in the mind of man, the noblest part of\nher noblest work.\n\nNo one supposes that there is any such inharmonious combination in\nthe organization of his physical frame, and the notion that it exists\nin his mental constitution, as it is founded in the grossest ignorance,\nso it is productive of incalculable mischief. In both, indeed, are\nmanifest two great powers, each distinct; each having its own peculiar\noperation; and the one being subservient to the other, but both\nconducing alike to one common end. By the addition of the apparatus of\nthe animal to that of the organic life, a nobler structure is built\nup than could have been framed by the organic alone: by the addition\nof the sympathetic to the selfish part of the mental constitution, a\nhappier being is formed than could have been produced by the selfish\nalone. And as the organic might have existed without the animal life,\nbut by the addition of the animal a new and superior being is formed,\nso might the selfish part of the mental constitution, and the pleasures\nthat flow from it, have existed alone; but by the addition of the\nsympathetic, a sum is added to enjoyment, of the amount of which some\nconception may be formed by considering what human life would be, with\nevery selfish appetite and faculty gratified in the fullest conceivable\ndegree, but without any admixture whatever of sympathetic or social\npleasure. Selfish enjoyment is not common. If any one set himself to\nexamine what at first view might seem a purely selfish pleasure, he\nwill soon be sensible that, of the elements composing any given state\nof mind to which he would be willing to affix the term pleasurable,\na vast preponderance consists of sympathetic associations. The more\naccurately he examine, and the farther he carry his analysis, the\nstronger will become his conviction, that a purely selfish enjoyment,\nthat is, a truly pleasurable state of mind, in no degree, mediately or\nimmediately, connected with the pleasurable state of another mind, is\nexceedingly rare.\n\nBut if the constitution of human nature and the structure of human\nsociety alike render it difficult for the human heart to be affected\nwith a pleasure in no degree derived from\u2014absolutely and totally\nunconnected with sympathetic association, of that complex pleasure\nwhich arises out of social intercourse, partly selfish and partly\nsympathetic, how far sweeter the sympathetic than the selfish\npart; and as the sympathetic preponderates over the selfish, how\nvast the increase of the pleasure! And when matured, exalted into\naffection\u2014affection, that holy emotion which exerts a transforming\ninfluence over the selfish part of human nature, turning it into the\nsympathetic; affection, which renders the happiness of the beloved\nobject inexpressibly dearer to the heart than its own; affection,\namong the benignant feelings of which as there is none sweeter so\nthere is none stronger than that of self-devotion, nay, sometimes even\nof self-sacrifice; affection, which is sympathy pure, concentrated,\nintense\u2014Oh how beautiful is the constitution of this part of our\nnature, by which the most transporting pleasures the heart receives are\nthe direct reflection of those it gives!\n\nNor ought it to be overlooked, that, while nearly all the selfish,\nlike all the sensual pleasures, cannot be increased beyond a fixed\nlimit, cannot be protracted beyond a given time, are short-lived in\nproportion as they are intense, and satiate the appetite they gratify,\nthe sympathetic pleasures are capable of indefinite augmentation; are\nabsolutely inexhaustible; no limit can be set to their number, and no\nbound to their growth; they excite the appetite they gratify; they\nmultiply with and by participation, and the more is taken from the\nfountain from which they flow, the deeper, the broader, and the fuller\nthe fountain itself becomes.\n\nBut not only is the mental state of affection in all its forms and\ndegrees highly pleasurable, but the very consciousness of being the\nobject of affection is another pleasure perfectly distinct from that\narising immediately from the affection itself. It has been said of\ncharity, that it is twice blessed, that it blesses alike him that\ngives and him that receives; but love has in it a threefold blessing:\nfirst, in the mental state itself; secondly, in the like mental state\nwhich the manifestation of it produces in another; and thirdly, in the\nmental state inseparable from the consciousness of being the object of\naffection. And this reflex happiness, this happiness arising from the\nconsciousness of being the object, is even sweeter than any connected\nwith being the subject of affection.\n\nIn like manner there is pleasure in the performance of beneficent\nactions; in energetic, constant, and therefore ultimately successful\nexertions to advance the great interests of human kind, in art, in\nscience, in philosophy, in education, in morals, in legislation,\nin government; whether those exertions are put forth in the study,\nthe school, the senate, or any less observed though perhaps not\nless arduous nor less important field of labour. Exertions of this\nkind beget in those for whom, towards those by whom, they are made,\nbenignant feelings\u2014respect, veneration, gratitude, love. With\nsuch feelings the philosopher, the instructor, the legislator, the\nstatesman, the philanthropist, knows that he is, or that, sooner or\nlater, he will be regarded by his fellow men; and in this consciousness\nthere is happiness: but this is another source of happiness perfectly\ndistinct from that arising from the performance of beneficent actions;\nit is a new happiness superadded to the former, and, if possible,\nstill more exquisite. Thus manifold is the beneficent operation of the\nsympathetic affection: thus admirable is the provision made in the\nconstitution of our nature for the excitement and extension of this\naffection, and, through its instrumentality, for the multiplication and\nexaltation of enjoyment!\n\nIn affections and actions of the class just referred to, and in the\npleasures that result from them, there is much of the nature which is\ncommonly termed moral. And the power to which the moral affections and\nactions are referred is usually and justly considered as the supreme\nfaculty of the mind; for it is the regulator and guide of all the\nothers; it is that by which they attain their proper and ultimate\nobject. Of whatever pleasure human nature is capable in sensation, in\nidea, in appetite, in passion, in emotion, in affection, in action;\nwhatever is productive of real pleasure, in contradistinction to what\nonly cheats with the false hope of pleasure; whatever is productive\nof pure pleasure, in contradistinction to what is productive partly\nof pleasure and partly of pain, and consequently productive not of\npure, but of mixed pleasure; whatever is productive of a great degree\nof pleasure in contradistinction to what is productive of a small\ndegree of pleasure; whatever is productive of lasting pleasure, in\ncontradistinction to what is productive of temporary pleasure; whatever\nis productive of ultimate pleasure, in contradistinction to what is\nproductive of immediate pleasure, but ultimate pain; this greatest and\nmost perfect pleasure it is the part of the moral faculty to discover.\nIn the degree in which the operation of this faculty is correct and\ncomplete, it enables the human being to derive from every faculty of\nhis nature the greatest, the purest, the most enduring pleasure; that\nis, the maximum of felicity. This is the proper scope and aim of the\nmoral faculty; to this its right exercise is uniformly conducive; and\nthis, as it is better cultivated and directed, it will accomplish in\na higher degree, in a continual progression, to which no limit can\nbe assigned. But if the operation of this faculty be to render every\nother in the highest degree conducive to happiness, conformity to\nthe course of conduct required by it, must of course be that highest\nhappiness. Conformity to the course of conduct pointed out by the\nmoral faculty as conducive in the highest degree to happiness is moral\nexcellence, or, in the definite and exact sense of the word, virtue.\nAnd in this sense it is that virtue is happiness. It is because it\ndiscriminates the true sources of happiness, that is, directs every\nother faculty into its proper course, and guides it in that course to\nthe attainment of its ultimate object, that the moral faculty is ranked\nas the highest faculty of the mind. Supposing the operation of this\nfaculty to be perfect, it is but an identical expression to say, that\nto follow its guidance implicitly is to follow the road that leads to\nthe most perfect happiness. But, over and above the happiness thus\ndirectly and necessarily resulting from yielding uniform and implicit\nobedience to the moral faculty, there is, in the very consciousness of\nsuch conformity, a new happiness, as pure as it is exalted. Thus, in\na twofold manner, is the moral the highest faculty of the mind, the\nsource of its highest happiness; and thus manifest it is, from every\nview that can be taken of the constitution of human nature, that every\nfaculty with which it is endowed, from the highest to the lowest, not\nonly affords its own proper and peculiar pleasure, but that each, as\nit successively rises in the scale, is proportionately the source of a\nnobler kind, and a larger amount of enjoyment.\n\nAnd the pleasure afforded by the various faculties with which the human\nbeing is endowed is the immediate and direct result of their exercise.\nWith the exception of the organic organs, and the reason for the\nexception in regard to them has been assigned, the action of the organs\nis directly pleasurable. From the exercise of the organs of sense, from\nthe operation of the intellectual faculties, from appetite, passion,\nand affection, pleasure flows as directly as the object for which the\ninstrument is expressly framed.\n\nAnd pleasure is the ordinary result of the action of the organs; pain\nis sometimes the result, but it is the extraordinary not the ordinary\nresult. Whatever may be the degree of pain occasionally produced, or\nhowever protracted its duration, yet it is never the natural, that\nis, the usual or permanent state, either of a single organ, or of an\napparatus, or of the system. The usual, the permanent, the natural\ncondition of each organ, and of the entire system, is pleasurable.\nAbstracting, therefore, from the aggregate amount of pleasure, the\naggregate amount of pain, the balance in favour of pleasure is immense.\nThis is true of the ordinary experience of ordinary men, even taking\ntheir physical and mental states such as they are at present; but the\nordinary physical and mental states, considered as sources of pleasure\nof every human being, might be prodigiously improved; and some attempt\nwill be made, in a subsequent part of this work, to show in what manner\nand to what extent.\n\nIt has been already stated that there are cases in which pleasure is\nmanifestly given for its own sake; in which it is rested in as an\nultimate object: but the converse is never found: in no case is the\nexcitement of pain gratuitous. Among all the examples of secretion,\nthere is no instance of a fluid, the object of which is to irritate\nand inflame: among all the actions of the economy, there is none, the\nobject of which is the production of pain.\n\nMoreover, all such action of the organs, as is productive of pleasure,\nis conducive to their complete development, and consequently to the\nincrease of their capacity for producing pleasure; while all such\naction of the organs as is productive of pain is preventive of their\ncomplete development, and consequently diminishes their capacity\nfor producing pain. The natural tendency of pleasure is to its own\naugmentation and perpetuity. Pain, on the contrary, is self-destructive.\n\nSpecial provision is made in the economy, for preventing pain\nfrom passing beyond a certain limit, and from enduring beyond a\ncertain time. Pain, when it reaches a certain intensity, deadens the\nsensibility of the sentient nerve; and when it lasts beyond a certain\ntime, it excites new actions in the organ affected, by which the organ\nis either restored to a sound state, or so changed in structure that\nits function is wholly abolished. But change of structure and abolition\nof function, if extensive and permanent, are incompatible with the\ncontinuance of life. If, then, the actions of the economy, excited by\npain, fail to put an end to suffering by restoring the diseased organ\nto a healthy state, they succeed in putting an end to it by terminating\nlife. Pain, therefore, cannot be so severe and lasting as materially to\npreponderate over pleasure, without soon proving destructive to life.\n\nBut the very reverse is the case with pleasure. All such action of the\norgans as is productive of pleasure is conducive to the perpetuation\nof life. There is a close connexion between happiness and longevity.\nEnjoyment is not only the end of life, but it is the only condition\nof life which is compatible with a protracted term of existence. The\nhappier a human being is, the longer he lives; the more he suffers,\nthe sooner he dies; to add to enjoyment, is to lengthen life; to\ninflict pain, is to shorten the duration of existence. As there is a\npoint of wretchedness beyond which life is not desirable, so there is\na point beyond which it is not maintainable. The man who has reached\nan advanced age cannot have been, upon the whole, an unhappy being;\nfor the infirmity and suffering which embitter life cut it short.\nEvery document by which the rate of mortality among large numbers of\nhuman beings can be correctly ascertained contains in it irresistible\nevidence of this truth. In every country, the average duration of life,\nwhether for the whole people or for particular classes, is invariably\nin the direct ratio of their means of felicity; while, on the other\nhand, the number of years which large portions of the population\nsurvive beyond the adult age may be taken as a certain test of the\nhappiness of the community. How clear must have been the perception of\nthis in the mind of the Jewish legislator when he made the promise,\nTHAT THY DAYS MAY BE LONG IN THE LAND WHICH THE LORD THY GOD HATH GIVEN\nTHEE\u2014the sanction of every religious observance, and the motive to\nevery moral duty!\n\nDeeply then are laid the fountains of happiness in the constitution\nof human nature. They spring from the depths of man's physical\norganization; and from the wider range of his mental constitution\nthey flow in streams magnificent and glorious. It is conceivable that\nfrom the first to the last moment of his existence, every human being\nmight drink of them to the full extent of his capacity. Why does he\nnot? The answer will be found in that to the following question. What\nmust happen before this be possible? The attainment of clear and just\nconceptions on subjects, in relation to which the knowledge hitherto\nacquired by the most enlightened men is imperfect. Physical nature,\nevery department of it, at least, which is capable of influencing\nhuman existence and human sensation; human nature, both the physical\nand the mental part of it; institutions so adapted to that nature\nas to be capable of securing to every individual, and to the whole\ncommunity, the maximum of happiness with the minimum of suffering\u2014this\nmust be known. But knowledge of this kind is of slow growth. To\nexpect the possession of it on the part of any man in such a stage of\ncivilization as the present, is to suppose a phenomenon to which there\nis nothing analogous in the history of the human mind. The human mind\nis equally incapable of making a violent discovery in any department of\nknowledge, and of taking a violent bound in any path of improvement.\nWhat we call discoveries and improvements are clear, decided, but\nfor the most part gentle, steps in advancement of the actual and\nimmediately-preceding state of knowledge. The human mind unravels the\ngreat chain of knowledge, link by link; when it is no longer able to\ntrace the connecting link, it is at a stand; the discoverer, in common\nwith his contemporaries, seeing the last ascertained link, and from\nthat led on by analogies which are not perceived by, or which do not\nimpress, others, at length descries the next in succession; this brings\ninto view new analogies, and so prepares the way for the discernment\nof another link; this again elicits other analogies which lead to the\ndetection of other links, and so the chain is lengthened. And no link,\nonce made out, is lost.\n\nChemists tell us that the adjustment of the component elements of\nwater is such, that although they readily admit of separation and are\nsubservient to their most important uses in the economy of nature\nby this very facility of decomposition, yet that their tendency to\nrecombination is equal, so that the quantity of water actually existing\nat this present moment in the globe is just the same as on the first\nday of the creation, neither the operations of nature, nor the purposes\nto which it has been applied by man, having used up, in the sense of\ndestroying, a single particle of it. Alike indestructible are the\nseparate truths that make up the great mass of human knowledge. In\ntheir ready divisibility and their manifold applications, some of\nthem may sometimes seem to be lost; but if they disappear, it is only\nto enter into new combinations, many of which themselves become new\ntruths, and so ultimately extend the boundaries of knowledge. Whatever\nmay have been the case in time past, when the loss of an important\ntruth, satisfactorily and practically established, may be supposed\npossible, such an event is inconceivable now when the art of printing\nat once multiplies a thousand records of it, and, with astonishing\nrapidity, makes it part and parcel of hundreds of thousands of minds.\nA thought more full of encouragement to those who labour for the\nimprovement of their fellow beings there cannot be. No onward step is\nlost; no onward step is final; every such step facilitates and secures\nanother. The savage state, that state in which gross selfishness seeks\nits object simply and directly by violence, is past. The semi-savage or\nbarbarous state, in which the grossness of the selfishness is somewhat\nabated, and the violence by which it seeks its object in some degree\nmitigated, by the higher faculties and the gentler affections of our\nnature, but in which war still predominates, is also past. To this has\nsucceeded the state in which we are at present, the so-called civilized\nstate\u2014a state in which the selfish principle still predominates, in\nwhich the justifiableness of seeking the accomplishment of selfish\npurposes by means of violence, that of war among the rest, is still\nrecognized, but in which violence is not the ordinary instrument\nemployed by selfishness, its ends being commonly accomplished by the\nmore silent, steady, and permanent operation of institutions. This\nstate, like the preceding, will pass away. How soon, in what precise\nmode, by what immediate agency, none can tell. But we are already\nin possession of the principle which will destroy the present and\nintroduce a better social condition, namely, the principle at the basis\nof the social union, THE MAXIMUM OF THE AGGREGATE OF HAPPINESS; THE\nMAXIMUM OF THE AGGREGATE OF HAPPINESS SOUGHT BY THE PROMOTION OF THE\nMAXIMUM OF INDIVIDUAL HAPPINESS!\n\n\n\n\nCHAPTER IV.\n\n  Relation between the physical condition and happiness, and\n  between happiness and longevity\u2014Longevity a good, and\n  why\u2014Epochs of life\u2014The age of maturity the only one that\n  admits of extension\u2014Proof of this from physiology\u2014Proof\n  from statistics\u2014Explanation of terms\u2014Life a fluctuating\n  quantity\u2014Amount of it possessed in ancient Rome: in modern\n  Europe: at present in England among the mass of the people\n  and among the higher classes.\n\n\nLife depends on the action of the organic organs. The action of the\norganic organs depends on certain physical agents. As each organic\norgan is duly supplied with the physical agent by which it carries on\nits respective process, and as it duly appropriates what it receives,\nthe perfection of the physical condition is attained; and, according to\nthe perfection or imperfection of the physical condition, supposing no\naccident interrupt its regular course, is the length or the brevity of\nlife.\n\nIt is conceivable that the physical condition might be brought to a\nhigh degree of perfection, the mind remaining in a state but little\nfitted for enjoyment; because it is necessary to enjoyment that there\nbe a certain development, occupation, and direction of the mental\npowers and affections: and the mental state may be neglected, while\nattention is paid to the physical processes. But the converse is not\npossible. The mental energies cannot be fully called forth while the\nphysical condition is neglected. Happiness presupposes a certain degree\nof excellence in the physical condition; and unless the physical\ncondition be brought to a high degree of excellence, there can be no\nsuch development, occupation, and direction of the mental powers and\naffections as is requisite to a high degree of enjoyment.\n\nThat state of the system in which the physical condition is sound is\nin itself conducive to enjoyment; while a permanent state of enjoyment\nis in its turn conducive to the soundness of the physical condition.\nIt is impossible to maintain the physical processes in a natural and\nvigorous condition if the mind be in a state of suffering. The bills\nof mortality contain no column exhibiting the number of persons who\nperish annually from bodily disease, produced by mental suffering;\nbut every one must occasionally have seen appalling examples of the\nfact. Every one must have observed the altered appearance of persons\nwho have sustained calamity. A misfortune, that struck to the heart,\nhappened to a person a year ago; observe him some time afterwards; he\nis wasted, worn, the miserable shadow of himself; inquire about him at\nthe distance of a few months, he is no more.\n\nIt is stated by M. Villerm\u00e9, that the ordinary rate of mortality in\nthe prisons of France, taking all together, is one in twenty-three\u2014a\nrate which corresponds to the age of sixty-five in the common course\nof life. But in the vast majority of cases the unfortunate victims\nof the law are no older than from twenty-five to forty-five years of\nage. Taking them at the mean age of thirty-five, it follows that the\nsuffering from imprisonment, and from the causes that lead to it, is\nequivalent to thirty years wear and tear of life. But this is not all;\nfor it is found that, during imprisonment, the ordinary chances of\ndeath are exactly quadrupled.\n\nIn regard to the whole population of a country, indigence may be\nassumed to be a fair measure of unhappiness, and wealth of happiness.\nIf the rate of mortality in the indigent class be compared with that\nof the wealthy, according to M. Villerm\u00e9, it will be found in some\ncases to be just double. Thus it is affirmed that, in some cases in\nFrance, taking equal numbers, where there are one hundred deaths in a\npoor arrondissement, there are only fifty in a rich; and that taking\ntogether the whole of the French population, human life is protracted\ntwelve years and a half among the wealthy beyond its duration among\nthe poor: consequently, in the one class, a child, newly born, has a\nprobability of living forty-two and a half years; in the other only\nthirty years.\n\nIn the great life-insurance establishments in England, a vast\nproportion of the persons who insure their lives are persons compelled\nto do so by their creditors; while three-fourths of those who\nvoluntarily insure their lives are professional men, living in great\ntowns, and experiencing the anxieties and fatigues, the hopes and\ndisappointments of professional life. In one of these establishments in\nLondon, out of 330 deaths that happened in twenty-six years preceding\nthe year 1831, it was found that eleven died by suicide, being one\nin thirty, implying the existence of an appalling amount of mental\nsuffering. The number of persons belonging to an insurance office who\nperish by suicide is sure to be accurately known, death by suicide\nrendering the policy void. It would be most erroneous to suppose that\nthese persons put an end to their existence under the mere influence of\nthe mental states of disappointment and despondency. The mind reacted\nupon the body: produced physical disease, probably inflammation of the\nbrain, and under the excitement of this physical disease, the acts of\nsuicide were committed. More than one case has come to my knowledge\nin which inflammation of the brain having been excited by mental\nsuffering, suicide was committed by cutting the throat. During the flow\nof blood, which was gradual, the brain was relieved; the mind became\nperfectly rational; and the patient might have been saved had a surgeon\nbeen upon the spot, or had the persons about the patient known where\nand how to apply the pressure of the finger to staunch the flow of\nblood, until surgical aid could be procured.\n\nBy a certain amount and intensity of misery life may be suddenly\ndestroyed; by a smaller amount and intensity, it may be slowly worn out\nand exhausted. The state of the mind affects the physical condition;\nbut the continuance of life is wholly dependent on the physical\ncondition: it follows that in the degree in which the state of the\nmind is capable of affecting the physical condition, it is capable of\ninfluencing the duration of life.\n\nWere the physical condition always perfect, and the mental state always\nthat of enjoyment, the duration of life would always be extended to\nthe utmost limit compatible with that of the organization of the\nbody. But as this fortunate concurrence seldom or never happens,\nhuman life seldom or never numbers the full measure of its days.\nUniform experience shows, however, that, provided no accident occur to\ninterrupt the usual course, in proportion as body and mind approximate\nto this state, life is long; and as they recede from it, it is short.\nImprovement of the physical condition affords a foundation for the\nimprovement of the mental state; improvement of the mental state\nimproves up to a certain point the physical condition; and in the ratio\nin which this twofold improvement is effected, the duration of life\nincreases.\n\nLongevity then is a good, in the first place, because it is a sign\nand a consequence of the possession of a certain amount of enjoyment;\nand in the second place, because this being the case, of course in\nproportion as the term of life is extended, the sum of enjoyment must\nbe augmented. And this view of longevity assigns the cause, and shows\nthe reasonableness of that desire for long life which is so universal\nand constant as to be commonly considered instinctive. Longevity and\nhappiness, if not invariably, are generally, co-incident.\n\nIf there may be happiness without longevity, the converse is not\npossible: there cannot be longevity without happiness. Unless the state\nof the body be that of tolerable health, and the state of the mind\nthat of tolerable enjoyment, long life is unattainable: these physical\nand mental conditions no longer existing, nor capable of existing, the\ndesire of life and the power of retaining it cease together.\n\nAn advanced term of life and decrepitude are commonly conceived to\nbe synonymous: the extension of life is vulgarly supposed to be the\nprotraction of the period of infirmity and suffering, that period which\nis characterized by a progressive diminution of the power of sensation,\nand a consequent and proportionate loss of the power of enjoyment, the\n\"sans teeth, sans eyes, sans taste, sans every thing.\" But this is so\nfar from being true, that it is not within the compass of human power\nto protract in any sensible degree the period of old age properly so\ncalled, that is, the stage of decrepitude. In this stage of existence,\nthe physical changes that successively take place clog, day by day, the\nvital machinery, until it can no longer play. In a space of time, fixed\nwithin narrow limits, the flame of life must then inevitably expire,\nfor the processes that feed it fail. But though, when fully come, the\nterm of old age cannot be extended, the coming of the term may be\npostponed. To the preceding stage, an indefinite number of years may be\nadded. And this is a fact of the deepest interest to human nature.\n\nThe division of human life into periods or epochs is not an arbitrary\ndistinction, but is founded on constitutional differences in the\nsystem, dependent on different physiological conditions. The periods\nof infancy, childhood, boyhood, adolescence, manhood, and old age, are\ndistinguished from each other by external characters, which are but\nthe outward signs of internal states. In physiological condition, the\ninfant differs from the child, the child from the boy, the boy from the\nman, and the adult from the old man, as much in physical strength as in\nmental power. There is an appointed order in which these several states\nsucceed each other; there is a fixed time at which one passes into\nanother. That order cannot be inverted: no considerable anticipation\nor postponement of that fixed time can be effected. In all places and\nunder all circumstances, at a given time, though not precisely at the\nsame time in all climates and under all modes of life, infancy passes\ninto childhood, childhood into boyhood, boyhood into adolescence, and\nadolescence into manhood. In the space of two years from its birth,\nevery infant has ceased to be an infant, and has become a child; in the\nspace of six years from this period, every male child will have become\na boy; add eight years to this time, and every boy will have become a\nyoung man; in eight years more, every young man will have become an\nadult man; and in the subsequent ten years, every adult man will have\nacquired his highest state of physical perfection. But at what period\nwill this state of physical perfection decline? What is the maximum\ntime during which it can retain its full vigour? Is that maximum fixed?\nIs there a certain number of years in which, by an inevitable law,\nevery adult man necessarily becomes an old man? Is precisely the same\nnumber of years appointed for this transition to every human being?\nCan no care add to that number? Can no imprudence take from it? Does\nthe physiological condition or the constitutional age of any two\nindividuals ever advance to precisely the same point in precisely the\nsame number of years? Physically and mentally, are not some persons\nolder at fifty than others are at seventy? And do not instances\noccasionally occur in which an old man, who reaches even his hundredth\nyear, retains as great a degree of juvenility as the majority of those\nwho attain to eighty?\n\nIf this be so, what follows? One of the most interesting consequences\nthat can be presented to the human mind. The duration of the periods of\ninfancy, childhood, boyhood, and adolescence, is fixed by a determinate\nnumber of years. Nothing can stay, nothing retard, the succession of\neach. Alike incapable of any material protraction is the period of old\nage. It follows that every year by which the term of human existence is\nextended is really added to the period of mature age; the period when\nthe organs of the body have attained their full growth and put forth\ntheir full strength; when the physical organization has acquired its\nutmost perfection; when the senses, the feelings, the emotions, the\npassions, the affections, are in the highest degree acute, intense,\nand varied; when the intellectual faculties, completely unfolded\nand developed, carry on their operations with the greatest vigour,\nsoundness, and continuity; in a word, when the individual is capable of\nreceiving and of communicating the largest amount of the highest kind\nof enjoyment.\n\nA consideration more full of encouragement, more animating, there\ncannot be. The extension of human life, in whatever mode and degree it\nmay be possible to extend it, is the protraction of that portion of it,\nand only of that portion of it, in which the human being is capable of\nRECEIVING AND OF COMMUNICATING THE LARGEST MEASURE OF THE NOBLEST KIND\nOF ENJOYMENT.\n\nConsiderations, purely physiological, establish this indubitably; but\nit is curious that a class of facts, totally different from those of a\nphysiological nature, equally prove it; namely, the results obtained\nfrom the observation of the actual numbers that die at different ages,\nand the knowledge consequently acquired of the progressive decrement\nof life. Mortality is subject to a law, the operation of which is as\nregular as that of gravitation. The labours of my valued friend Mr.\nFinlaison, the actuary of the National Debt, have not only determined\nwhat that law is in relation to different nations at different periods\nof their history, but this celebrated calculator has also invented a\nstriking mode of expressing and representing the fact. He constructed\na chart on which 100 perpendicular lines, answering to the respective\nages of human life, are laid down and numbered in succession. These\nare crossed at right angles by 500 horizontal lines; so that, in the\nmanner of musical notation, a point may be laid down either on the\nhorizontal line, or on the space between any two of them: and thus,\n1000 points may be laid down on each of the perpendicular lines. The\nhorizontal lines are in like manner numbered from 1 to 1000, ascending\nfrom the base. Taking any observation which shows the number of living\npersons that commence, and in like manner the number that die in each\nparticular year of human life, the calculator reduced by the rule of\nthree every such actual number of living persons for every separate\nyear to 10,000: he next showed the corresponding proportion of deaths\nout of such 10,000. These proportions he represented on the chart by\na point inserted on the horizontal line or space for the number of\ndeaths, and on the perpendicular line for the particular age. He then\nconnected all the points so laid down, and the result is a curve,\nrepresenting the track of death through an equal number of human beings\nexisting at each age of life. As the curve rises on the perpendicular\nline, at any given age, it indicates by so much an increase of the\nmortality at that age; and as the curve falls, the reverse is denoted.\n\nNow, it is a highly interesting fact, that the curves on this chart\ndrawn upon it before the physiological phenomena were known to the\noperator, placed there because such he found to be the actual path\nalong which death marshals his course, exactly correspond to the epochs\nwhich physiology teaches to be determinate stages of human existence.\nThe infant, the child, the boy, the adolescent, the man, the old man,\nare not exposed to the same danger. The liability of each to death\nis not merely different; it is widely different; the liability of\neach class is uniformly the same, the circumstances influencing life\nremaining the same; and under no known change of circumstances does\nthe relative liability of the class vary; under no change does the\nliability of the adolescent become that of the infant, or the liability\nof the adult that of the aged. Take from any statistical document any\nnumber of persons; observe out of this number the proportion that\ndies at the different stages just enumerated; and the period of human\nlife which admits of extension will be strikingly manifest. Take with\nthis view the Prussian statistical tables, the general correctness of\nwhich is admitted. From these tables it appears, and the correctness\nof the result is confirmed by a multitude of other tables, that out\nof a million living male births, there will die in the first year of\nlife 180,492 infants, and out of the like number of living female\nbirths, there will die 154,705 infants. Let us follow up the decrement\nof life through the different epochs of human existence, confining\nour observations to the male sex, in which the development is more\nemphatically marked.\n\nIn Mr. Finlaison's report, printed by the House of Commons on the 30th\nof March, 1829, there are six original observations on the mortality of\nas many separate sets of annuitants of the male sex.\n\nFrom an examination and comparison of these observations, it\nappears\u20141st. That the rate of mortality falls to a minimum at\nthe close of the period of childhood. 2d. That from this point\nthe mortality rises until the termination of adolescence or the\ncommencement of adult age. 3d. That from the commencement of adult age\nthe mortality again declines, and continues to decline to the period of\nperfect maturity. And 4th. That from the period of perfect maturity,\nthe mortality rises, and uniformly, without a single exception,\nreturns, at the age of forty-eight, to the point at which it stood at\nthe termination of adolescence. These results clearly indicate that\ncertain fixed periods are marked by nature as epochs of human life;\nand that at the date of the recorded facts which furnish the data\nfor these observations, and as far as regards the class of persons\nto which they relate, the age of forty-eight was the exact point at\nwhich the meridian of life was just passed, and a new epoch began. The\nfollowing table exhibits at one view the exact results of each of the\nobservations. For example,\n\n  According to The mortality   From whence  From this  And from this\n      the          is at a       it rises   point it    age it again\n  observation,  minimum at the   until      declines   rises, but is not\n      No.           age of     the age of    to the     equal to the\n                                             age of      mortality in\n                                                       the 2d column\n                                                       until the age of\n\n       15   \u2014     13      \u2014     23    \u2014     34   \u2014     48\n\n       16   \u2014     13      \u2014     23    \u2014     35   \u2014     48\n\n       17   \u2014     14      \u2014     22    \u2014     33   \u2014     48\n\n       18   \u2014     13      \u2014     23    \u2014     33   \u2014     48\n\n       19   \u2014     13      \u2014     24    \u2014     34   \u2014     48\n\n       20   \u2014     13      \u2014     24    \u2014     34   \u2014     48\n\nThe observation, No. 15, is founded on the large mass of 9,347 lives\nand 4,870 deaths. From this observation, it appears that, at the age of\nthirteen, the mortality out of a million is 5,742, being 174,750 less\nthan in the first year of infancy At the age of twenty-three, it is\n15,074, being 9,332 more than at the close of childhood. At the age of\nthirty-four, the period of complete manhood, it falls to 11,707, being\n3,367 less than at the close of adolescence. At the age of forty-eight,\nthe mortality returns to 14,870, all but identically the same as at\ntwenty-three, the adult age. From the age of forty-eight, when, as\nhas been stated, life just begins to decline from its meridian, the\nmortality advances slowly, but in a steady and regular progression.\nThus, at the age of fifty-eight it is 29,185, being 14,315 more than\nat the preceding decade, or almost exactly double. At the age of\nsixty-eight, it is 61,741, being 32,556 more than at the preceding\ndecade, or more than double. At the age of seventy-eight, it is\n114,255, being 52,514 more than at the preceding decade. At the age of\neighty-eight, it is 246,803, being 132,548 more than at the preceding\ndecade.\n\nDuring the first year of infancy, as has been shown, the mortality\nout of a million is 180,492. At the extreme age of eighty-four, it\nis 178,130, very nearly the same as in the first year of infancy.\nGreatly as the mortality of all the other epochs of life is affected\nby country, by station, by a multitude of influences arising out of\nthese and similar circumstances; yet the concurrent evidence of all\nobservation shows that at this and the like advanced ages the mean term\nof existence is nearly the same in all countries, at all periods, and\namong all classes of society. Thus, among the nobility and gentry of\nEngland, the expectation of life at eighty-four is four years; among\nthe poor fishermen of Ostend, it is precisely the same. M. De Parcieux,\nwho wrote just ninety years ago, establishes the expectation of life\nat that time in France, at the same age, to have been three and a half\nyears; and Halley, who wrote 120 years ago, and whose observations are\nderived from documents which go back to the end of the seventeenth\ncentury, states the expectation of life at eighty-four to be two years\nand nine months.\n\nFrom these statements, then, it is obvious, that from the termination\nof infancy at three years of age, a decade of years brings childhood to\na close, during which the mortality, steadily decreasing, comes to its\nminimum. Another decade terminates the period of adolescence, during\nwhich the mortality as steadily advances. A third decade changes the\nyoung adult into a perfect man, and during this period, the golden\ndecade of human life, the mortality again diminishes; while, during\nanother decade and a half, the mortality slowly rises, and returns\nat the close of the period to the precise point at which it stood at\nadult age. Thus the interval between the period of birth and that of\nadult age includes a term of twenty-three years. The interval between\nthe period of adult age and that when life just begins to decline from\nits meridian, includes a term of twenty-four years: consequently, a\nperiod more than equal to all the other epochs of life from birth\nto adult age is enjoyed, during which mortality makes no advance\nwhatever. Now the term of years included in the several epochs that\nintervene between birth and adult age is rigidly fixed. Thus the\nperiod of infancy includes precisely three years, that of childhood\nten years, and that of adolescence ten years. Within the space of time\ncomprehended in these intervals, physiological changes take place,\non which depend every thing that is peculiar to the epochs. These\nchanges cannot be anticipated, cannot be retarded, except in a very\nslight degree. In all countries, among all classes, they take place in\nthe same order and nearly in the same space of time. In like manner,\nin extreme old age, or the age of decrepitude, which may be safely\nassumed to commence at the period when the mortality equals that of the\nfirst year of infancy, namely, the age of eighty-four, physiological\nchanges take place, which, within a given space of time, inevitably\nbring life to a close. That space of time, in all countries, in all\nranks, in all ages, or rather as far back as any records enable us to\ntrace the facts, appears to be the same. As within a given time the\nboy must ripen into manhood, so within a given time the man of extreme\nold age must be the victim of death. Consequently, it is the interval\nbetween the adult age and the age of decrepitude, and only this, that\nis capable of extension. During the interval between adult age and the\nperfect meridian of life, comprehending at present, as we have seen,\na period of twenty-four years, the constitution remains stationary,\nmortality making no sensible inroad upon it. But there is no known\nreason why this stationary or mature period of life should, like\nthe determinate epochs, be limited to a fixed term of years. On the\ncontrary, we do in fact know that it is not fixed; for we know that the\nphysiological changes on which age depends are, in some cases, greatly\nanticipated, and in others, proportionately postponed; so that some\npersons are younger at sixty, and even at seventy, than others are at\nfifty; whereas, an analogous anticipation or postponement of the other\nepochs of life is never witnessed. So complete is the proof, that the\nextension of human life can consist in the protraction neither of the\nperiod of juvenility, nor in that of senility, but only in that of\nmaturity.\n\nWere it necessary to adduce further evidence of this most interesting\nfact, it would be found equally in the statistics of disease as\nin those of mortality. Indeed, the evidence derived from both\nthese sources must be analogous, because mortality is invariably\nproportionate to the causes of mortality, of which causes, sickness, in\nall its forms, may be taken as the general or collective expression.\n\nWe do not possess the same means of illustrating the prevalence\nof disease through all the epochs of life as we do of showing the\nintensity of mortality; yet the report of Mr. Finlaison, already\nreferred to, enables us to show its comparative prevalence at several\nof those stages. Thus, from this document, it appears, that among\nthe industrious poor of London, members of benefit societies, out\nof a million of males, the proportion constantly sick at the age of\ntwenty-three, is 19,410; at the age of twenty-eight, it is 19,670; at\nthe age of thirty-three, it is 19,400; at the age of thirty-eight,\nit is 23,870; at the age of forty-three, it is 26,260; at the age of\nforty-eight, it is 26,140; at the age of fifty-three, it is 27,060;\nat the age of fifty-eight, it is 36,980; at the age of sixty-three,\nit is 57,000; at the age of sixty-eight, it is 108,040; at the age of\nseventy-three and upwards, it is 317,230. The prevalence of sickness\nis not an exact and invariable measure of the intensity of mortality;\nbut there is a close connexion between them, as is manifest from\nthe progressively increasing amount of sickness, as age advances.\nThus, in the first ten years from the age of twenty-three to that of\nthirty-three, there is no increase of sickness, its prevalence is\nall but identically the same; in the next ten years from the age of\nthirty-three to that of forty-three, the increase of sickness, as\ncompared with that of the preceding decade, is 6,860; in the next ten\nyears from the age of forty-three to that of fifty-three, the increase\nis only 800; in the next ten years from the age of fifty-three to\nthat of sixty-three, the increase is 29,940, while from the age of\nsixty-three to seventy-three, it is 260,230.\n\nSuch are the results derived from the experience of disease considered\nin the aggregate, all its varied forms taken together. I am enabled\nfurther to present an exact and most instructive proof, that one\nparticular disease which, in this point of view, may be considered\nas more important than any other, because it is the grand agent of\ndeath, namely fever, carries on its ravages in a ratio which steadily\nand uniformly increases as the age of its victim advances. Having\nsubmitted the experience of the London Fever Hospital for the ten\nyears preceding January 1834, an observation including nearly 6,000\npatients affected with this malady, to Mr. Finlaison, it was subjected\nby him to calculation. Among other curious and instructive results to\nbe stated hereafter, it was found that the mortality of fever resolves\nitself into the following remarkable progression. Thus suppose 100,000\npatients to be attacked with this disease between the ages of 5 and\n16, of these there would die - 8,266 and of an equal number\n\n    between 15 and 26   there would die  11,494\n            25 and 36      \"    \"    \"   17,071\n            35 and 46      \"    \"    \"   21,960\n            45 and 56      \"    \"    \"   30,493\n            55 and 66      \"    \"    \"   40,708\n            65 and upwards \"    \"    \"   44,643\n\nThus the risk of life from this malady is twice as great at the age\nof thirty-one as it is at eleven. It is also nearly twice as great\nat forty-one as it is at twenty-one. It is five times as great at\nsixty-one as it is at eleven, and nearly four times as great above\nsixty-five as it is at twenty-one.\n\nFrom the whole of the foregoing statements, it is manifest that life is\na fluctuating quantity. In order to compare this fluctuating quantity\nunder different circumstances, writers on this branch of statistics use\nseveral terms, the exact meaning of which it is desirable to explain.\nIt is, for example, very important to have a clear understanding of\nwhat is meant by such expressions as the following: the expectation,\nthe probability, the value, the decrement of life, and the law of\nmortality.\n\n1. THE EXPECTATION OF LIFE. It is important to bear in mind that\nseveral expressions in common use have a signification perfectly\nsynonymous with this: namely, _share of existence_; _mean duration of\nlife_; _la vie moyenne_.\n\nBy these terms is expressed the total number of years, including also\nthe fractional parts of a year, ordinarily attained by human beings\nfrom and after any given age. Suppose, for example, that one thousand\npersons enter on the eighty-sixth year of their age: suppose the\nnumber of years and days which each one of them lives afterwards be\nobserved and recorded; suppose the number ultimately attained by each\nbe formed into a sum total; suppose this total be divided equally among\nthe thousand, the quotient of this division is said to be each one's\nshare of existence, or his mean duration of life, or his expectation\nof life. Thus, of the thousand persons in the present case supposed\nto commence the age of eighty-five, suppose the number of years they\ncollectively attain amount to 3,500 years: the one-thousandth part of\n3,500 is three and a half: three years and a half then is said to be\nthe expectation of life at the age of eighty-five, because, of all the\npersons originally starting, this is the equal share of existence that\nfalls to the lot of each.\n\n2. PROBABILITY OF LIFE; or _the probable duration of life_, _la vie\nprobable_. These are synonymous terms, in use chiefly among continental\nwriters as an expression of the comparative duration of life. The\ntabular methods of setting forth the duration of life consist, for the\nmost part, in assuming that 10,000 infants are born; and that at the\nage of one, two, three, and each successive year of life, there are\nso many still remaining in existence. Fix on any age; observe what\nnumber remain alive to commence that age; note at what age this number\ndecreases to one-half; the age at which they so come to one-half is\ncalled the probable term of life; because, say the continental writers,\nit is an equal wager whether a person shall or shall not be alive at\nthat period. Thus, suppose one thousand males commence together the age\nof eighty-four; suppose the table indicate that there will be alive\nat the age of eighty-five, 817; at the age of eighty-six, 648; at the\nage of eighty-seven, 493; at the age of eighty-eight, 357, and so on.\nIn the present case, the probable duration of life at eighty-four is\nsaid to be very nearly three years, because, at the age of eighty-seven\nthere are left alive 493, very nearly one-half of the thousand that\noriginally started together.\n\n3. VALUE OF LIFE. This term, when used accurately, expresses the\nduration of life as measured by one or other of the methods already\nexpounded. But it is sometimes popularly used in a loose and singularly\ninaccurate sense. Thus it is very commonly said\u2014\"Such a man's life\nis not worth ten years' purchase,\" which is the same thing as to say,\nthat an annuity, suppose a hundred pounds a year, payable during the\nlife of the person in question, is not worth ten times its magnitude,\nthat is one thousand pounds. If a thousand pounds be put into a bank\nat some rate of interest to be agreed upon, and if a hundred pounds be\ndrawn every year from the stock, the expression under consideration\naffirms that the person in question will be dead before the principal\nand interest are exhausted. For instance, at four per cent., the value\nof an annuity of one hundred pounds to a man of the age of twenty-five\nis 1694_l._, which is 16-9/10 years' purchase; whereas, his expectation\nof life at that age is 35-9/10 years.\n\n4. LAW OF MORTALITY. By this term is expressed the proportion out of\nany determinate number of human beings who enter on a given year of\nage, that will die in that year. Every observation on the duration of\nlife presents certain numbers, which, by recorded facts, are found to\npass through each year of age, and also shows how many have died or\nfailed to pass through every year of age. Those numbers, by the rule\nof three, are converted into the proportions who would die at each\nage out of one million of persons, if such a number had commenced it.\nSuppose, then, a million of persons to be in existence at the first\nyear of age; suppose a million to be in existence at the second year\nof age; suppose a million to be in existence at the third year of\nage; and in this manner suppose an equal number to be in existence at\nthe commencement of each and every year to the extreme term of human\nlife. Now, the proportions that by actual observation are found to\ndie at each and every year out of the million that were alive at the\ncommencement of it, form separately the law of mortality for each year,\nand collectively for the whole of life.\n\n5. DECREMENT OF LIFE. Assuming, as before, that a million of male\nchildren are born alive (for the still-born must be excluded from\nthe calculation) if it be found that 180,492 would die in the first\nyear, it follows that the difference, namely, 819,508, will enter upon\nthe age of one year. Suppose the law of mortality indicate that the\nproportion that will die, out of a million, between the age of one\nand two, is 30,000; it is plain that the number who would die out of\n819,508 will by the rule of three be 27,863, and consequently that the\nresidue, namely, 791,615, will remain alive, and so enter on the age\nof two years. This method being pursued through each and every age to\nthe extreme term of life, when none of the original million survive,\nthe result is a table of mortality in the form in which it is commonly\npresented in the works of writers on this branch of science. In the\ntable thus constructed there is a column containing the number of\nliving persons who, out of the original million, lived to enter upon\neach and every year. Of this rank of numbers the difference between\neach term and its next succeeding one, is the number who die in that\nparticular interval: that number is the measure of what is technically\ncalled the decrement of life for that particular year, and the whole\nof the decrements for each and every year taken collectively is termed\nthe decrement of life. The decrement of life, then, is not only not\nthe same as the law of mortality, but is carefully to be distinguished\nfrom it. The law of mortality is derived from observing the number\nwho die out of one and the same number which is always supposed to\nenter on each and every year. The decrement of life constitutes a\nrank of numbers arising out of the successive deaths; that is, out of\nthe original million in the first year; out of the survivors of that\nmillion in the second year; out of the survivors of those survivors in\nthe third year, and so on. In the first case the number of the living\nis always the same; the number that die is the variable quantity: in\nthe second case the number of the living is the variable quantity,\nwhile the number that die may remain pretty much the same for a\nsuccession of years; and on casting the eye on the tables constructed\nin the ordinary mode, it will be seen that the number often does remain\nthe same for a considerable series of years.\n\nWe have said that life is a fluctuating quantity. It fluctuates\nin different countries at the same period; in the same country at\ndifferent periods; in the same country, at the same period, in\ndifferent places; in the same country, at the same period, in the\nsame place, among different classes; in the same country, at the same\nperiod, in the same place, among the same class, at the different\ndeterminate stages of life. Some few of these fluctuations, and\nmore especially the last, depend on the primary constitution of the\norganization in which life itself has its seat, over which man has\nlittle or no control. The greater part of them depend on external\nand adventitious agencies over which man has complete control. Human\nignorance, apathy, and indolence, may render the duration of life, in\nregard to large classes and entire countries, short; human knowledge,\nenergy and perseverance, may extend the duration of life far beyond\nwhat is commonly imagined. It will be interesting and instructive to\nselect a few of the more striking examples of this from the records we\npossess, few and imperfect as they are, in relation to this subject.\n\nOf the duration of life in the earlier periods of the history of the\nhuman race we know nothing with exactness, though there are incidental\nstatements which afford the means of deducing with some probability\nthe rate of mortality in particular situations. There has come down to\nus one document through Domitius Ulpianus, a judge, who flourished in\nthe reign of Alexander Severus, which enables us to form a probable\nconjecture at least of the opinion of the Roman people of the value\nof life among the citizens of Rome in that age. It happened at Rome\nas in other countries, that when an estate came into the possession\nof an individual it was burthened with a provision for another person\nduring the life of the latter, a younger brother, for example. This\nprovision was called by the Romans an aliment. No estate, burthened\nwith such a provision, could be sold by the heir in possession, unless\nthe purchaser retained in his hands so much of the price as was deemed\nadequate to secure the regular and continuous payment of the aliment.\nThis imposed upon the Romans the necessity of considering what the term\nof life would probably be from and after any given age. What they did\nconceive that term to be is stated in a document of Ulpianus, recorded\nby Justinian, and given in the note below.[1] This document imports\nthat from infancy up to the age of\n\n                      20       there should be allowed 30 years\n                 From 20 to 25   \"     \"     \"     \"   28   \"\n                      25 to 30   \"     \"     \"     \"   25   \"\n                      30 to 35   \"     \"     \"     \"   22   \"\n                      35 to 40   \"     \"     \"     \"   20   \"\n                        \u2014\u2014\u2014\u2014\n                From  50 to 55   \"     \"     \"     \"    9   \"\n                      55 to 60   \"     \"     \"     \"    7   \"\n      And at all ages above 60   \"     \"     \"     \"    5   \"\n\nBut between 40 and 50, as many years were to be allowed as the age of\nthe party fell short of 60, deducting one year.\n\nNo clue has hitherto been obtained to the discovery of the real\nmeaning of this document. It is, however, highly probable that the\nRomans had fallen on one of the two methods of measuring the value of\nlife already explained; namely, that termed the Probability of Life.\nOf the two modes of determining the value of life, the probability was\nmore likely to occur to a Roman judge than the expectation. He had\nno tables, no registers to guide him. What course, then, would he be\nlikely to take? Probably he would form a list of his own school-fellows\nand others within his own knowledge, of the age, say, of twenty. By\nprevailing on persons of his own age, on whose correctness he could\nrely, to draw out similar lists, he might accumulate some thousand\nnames. In this list it is probable that the male sex alone would be\nincluded, on account of the greater ease of ascertaining both their\nexact age and the exact date of their death. For the same reason,\nit is probable that the list would consist only of the nobility and\nthe inhabitants of towns. Having thus completed his list, the next\nstep would be to frame another list of all who died at the age of\ntwenty-one; and next, another list of all who died at the age of\ntwenty-two, and so on through each and every year of life. Now by\nsubtracting the number in the list, No. 1, that is, those who died\nbetween twenty and twenty-one, from the number who originally started\nat twenty, which, in other words, would be to find the decrement of\nlife, in the mode already explained, he would see how many lived to\ncommence the age of twenty-one, and so on, through each year of life.\nBut this would be to construct a table, showing the probable duration\nof life; that is, a table from which he could observe at what advanced\nage the number originally starting at twenty, and so on, came to\ndiminish to one-half, when it would naturally occur to him that it\nis an equal wager whether such younger life would or would not be in\nexistence at the advanced age so ascertained. If we suppose this to\nhave been the method actually adopted by the Roman judge, and apply\nit to the table of Ulpianus, the result obtained is consistent in an\nextraordinary degree, and is highly interesting.\n\nThere is reason to believe that the mortality at present throughout\nEurope, taking all countries together, including towns and villages,\nand combining all classes into one aggregate, is one in thirty-six.\nS\u00fcssmilch, a celebrated German writer, who flourished about the middle\nof the last century, estimated it at this average at that period. The\nresult of all Mr. Finlaison's investigations is a conviction that the\naverage for the whole of Europe does not materially differ at the\npresent time. He has ascertained by an actual observation, that in the\nyear 1832 it was precisely this in the town of Ostend. Taking this\ntown, then, as the subject of comparison, it is found that the probable\nduration of life among the male sex at Ostend exceeds the Roman\nallowance by the following number of years; namely,\n\n  At the age of 17, the excess in round\n                    numbers is    5 years.\n                22     \"     \"    5\n                27     \"     \"    5\n                32     \"     \"    5\n                37     \"     \"    3\n                42     \"     \"    3\n                47     \"     \"    5\n                52     \"     \"    5\n                57     \"     \"    4\n                62     \"     \"    4\n                67     \"     \"    2\n                72     \"     \"    1\n                77     \"     \"    0\n\nBut it is not improbable that the Romans made some deduction from\nwhat they knew to be the real value of life among the citizens of\nRome, on account of the use of the money appropriated to the aliment,\nwhich the purchaser of the estate retained in his own hands. It has\nbeen shown that the average mortality at present at Ostend is one\nin thirty-six; which is the same thing as to assert that a new-born\nchild at Ostend has an expectation of thirty-five and a half years\nof life. The Roman allowance from birth, _\u00e0 prim\u00e2 \u00e6tate_, was thirty\nyears. If we suppose the Romans deducted from the real value of life\nfive and a half years for the interest of money, it would bring the\nRoman allowance and the duration of life at Ostend to the same. The\nlike deduction at the age of seventeen would likewise bring the\nprobability of life in both cases to the same. It is not likely that\nthe Romans, without any record of the individual facts, and acting\nonly on a general principle of utility, the best they could find,\nwould make any variation for the intermediate years of childhood and\nyouth: consequently the presumption is, that the duration of life at\nRome, 1300 years ago, was very much the same as it is throughout Europe\nat the present day. This estimate, however, for the reasons already\nassigned, includes only the resident citizens of Rome, the male sex,\nand the higher classes. What the mortality was at Rome among the lower\nclass, including the slaves\u2014what it was in the Roman provinces, and in\nthe less civilized countries of that age\u2014we have no means of forming\neven a conjecture. What it was in Europe during the succeeding ages\nof barbarism we do not know. In civilized Rome, the value of life\nhad probably reached a very high point; in barbarian Europe we may\nbe sure it fell to an exceedingly low point. From that low point, in\ncivilized Europe, it has been slowly but gradually rising, until, in\nmodern times, the whole mass of the European population has, to say\nthe very least, reached the highest point attained by the select class\nin ancient Rome. But in some favoured spots in Europe, the whole mass\nhas advanced considerably beyond the select class in ancient Rome. In\nEngland, for example, the expectation of life, at the present day, for\nthe mass of the people, as compared with that of the mass at Ostend,\nwhich, as has been shown, is the same as that of the whole of Europe,\nis as follows:\u2014\n\n  At birth   41\u00bd years.\n  At 12      46\u00be\n     17      41\u00bd\n     22      38\u215c\n     27      35\u00bc\n     32      32\n     37      28\u00be\n     42      25\u00bd\n     47      22\u00bc\n     52      19\n     57      16\n     62      13\n     67      10\u00bd\n     72       8\n     77       6\n\nIt should be borne in mind that the females of the mass exceed in\nduration the lives of the males at every age by two or three years.\n\nThe earliest statistical document bearing on the rate of mortality, in\nany European nation, emerging from the state of barbarism, appears to\nbe a manuscript of the fourteenth century, relating to the mortality\nof Paris, from which M. Villerm\u00e9 has calculated that the mortality\nof Paris at that period was one in sixteen. How the individual facts\ncontained in this manuscript were collected, from which M. Villerm\u00e9's\ncalculation is made, does not appear; and it makes the mortality so\nexcessive as to be altogether incredible. Yet a statement scarcely\nless extraordinary is made with regard to Stockholm, in the middle of\nthe last century. From a table given by Dr. Price, vol. ii., p. 411,\nit appears that, for all Sweden, between the years 1756 and 1763, the\nexpectation of life\n\n  Of males at birth, was      Females,\n        33\u00bc years.           35\u00be years.\n\nwhile at the same time it was at Stockholm,\n\n  For males at birth,         Females,\n        14\u00bc years.            18 years.\n\nWhereas, for the twenty years preceding 1800, it was, for all Sweden,\nat birth,\n\n  Males,       Females,\n   34\u00be.          37\u00bd.\n\nHitherto, in all places which man has made his abode, noxious agents\nhave been present which act injuriously upon his body, tending to\ndisturb the actions of its economy, and ultimately to extinguish life.\nAll these noxious agents, of whatever name or quality, may be included\nunder the term Causes of Mortality. Inherent in the constitution of the\nbody are conservative powers, the tendency of which is to resist the\ninfluence of these causes of mortality. The actual mortality at all\ntimes will of course be according to the relative strength of these\ndestructive agents, and the relative weakness of these conservative\npowers. There are states of the system tending to enfeeble these\nconservative powers. Such states become tests, often exceedingly\ndelicate, of the presence and power of the destructive agents to which\nthe body is exposed; and such, more especially, are, the states of\nparturition, infancy, and sickness. During the prevalence of these\nstates, in which the conservative powers of the body are weak, life\nis destroyed by causes which do not prove mortal in other conditions\nof the system. Accordingly, in every age and country, the rate of\nmortality among its lying-in women, its infants and its sick, may\nbe taken as a measure of the degree in which the state of the whole\npopulation is favourable or unfavourable to life.\n\nThe change that has taken place in the condition of lying-in women\nduring the last century in all the nations of Europe cannot be\ncontemplated without astonishment. The mortality of lying-in women in\nFrance, at the H\u00f4tel Dieu of Paris, in 1780, is stated to have been\none in 15. In 1817, for the whole kingdom of Prussia, including all\nranks, it was one in 112. In England, in the year 1750, at the British\nLying-in Hospital of London, it was one in 42; in 1780, it diminished\nto one in 60; in the years between 1789 and 1798, it further decreased\nto one in 288; in 1822, at the Lying-in Hospital of Dublin, it was no\nmore than one in 223; while during the last fifteen years at Lewes, a\nhealthy provincial town, out of 2410 cases there have been only two\ndeaths, that is, one in 1205. There is no reason to suppose that the\nmortality in the state of parturition is less at Lewes than in any\nother equally healthy country-town in England.\n\nEqually striking is the proof of the diminished violence of the\nprevalent causes of disease and death derived from the diminished\nmortality of children, the vital power of resistance being always\ncomparatively weak in the human infant, and consequently, the agents\nthat prove destructive to life exerting their main force on the new\nborn, and on those of tender age. From mortuary tables, preserved with\nconsiderable accuracy at Geneva since the year 1566, it appears that at\nthe time of the Reformation one-half of the children born died within\nthe sixth year; in the seventeenth century, not till within the twelfth\nyear; in the eighteenth century, not until the twenty-seventh year;\nconsequently, in the space of about three centuries, the probability\nthat a child born in Geneva would arrive at maturity has increased\nfivefold. In the present day, at Ostend, only half of the new-born\nchildren attain the age of thirty; whereas, in England, they attain the\nage of forty-five.\n\nNo less remarkable is the progressive diminution of mortality among\nthe sick of all ages. Hippocrates has left a statement, which has come\ndown to our times, of the history and fate of forty-two cases of acute\ndisease. Out of this number, thirty-seven were cases of continued\nfever; of these thirty-seven febrile cases twenty-one died, above half\nof the whole. The remaining five were cases of local inflammation,\nand of these four were fatal; thus, of the whole number of the sick\n(forty-two), twenty-five were lost. Now, even in the Fever Hospital of\nLondon, to which, for the most part, only the worst cases that occur\nin the metropolis are sent, and even of these many not until so late\na period of the disease that all hope of recovery is extinct, the\nmortality ranges in different years from one in six to one in twelve;\nand for a period of ten consecutive years, it is no more than one in\nseven; while, in the Dublin Fever Hospital, where most of the cases are\nsent very early, the average mortality from 1804 to 1812 was one in\ntwelve. At the Imperial Hospital at Petersburg, the average mortality\nfor fourteen years, ending in 1817, was one in four and a half. In the\nCharit\u00e9 of Berlin, on an average of twenty years, from 1796 to 1817,\nit was one in six. At Dresden, it was one in seven; at Munich, it was\none in nine, the lowest of any hospital of equal size in Germany. In\nthe year 1685, the average mortality at St. Bartholomew's and St.\nThomas's Hospitals was from one in seven to one in ten. During the ten\nyears from 1773 to 1783, it decreased to one in fourteen. From 1803 to\n1813, it was one in sixteen. The average for fifty years from 1764 to\n1813, was one in fifteen. In the smaller towns, the mortality is still\nless. It is less in Edinburgh and Dublin than in London; while in the\nhospital at Bath during 1827, even among the physician's patients, the\nmortality was only one in twenty. In the German provincial towns, the\ndiminution is still more remarkable. In the hospital at Gottingen, for\nexample, it is only one in twenty-one.\n\nIf the accuracy of these statements could be relied on, they\nwould not only afford striking illustrations of the well-known fact\nthat extraordinary differences prevail in the rate of mortality\nin different places, at different periods, and under different\ncircumstances; but they would further prove that, during the last\ncentury, a steady and progressive diminution of mortality has taken\nplace in all the countries of Europe. But of the truth of this there\nis much more certain evidence than can be derived from calculations,\nthe trustworthiness of the data of which is not established, and\nthe correctness of the calculators not known. Both the fluctuations\nof mortality and the increase in the value of life in the different\ncountries of Europe, from the earliest period when statistical facts\nbegan to be collected and compared, are exhibited in a striking\npoint of view in the following table, drawn up by Mr. Finlaison. The\nfacts relating to selected lives and to the mass of the people are\ndistinguished from each other, in order that they may be contrasted.\nThe data are derived from the most authentic sources, and the\ncalculations are made by men of the highest authority.\n\n\nLet it be conceived, that at each   50  55  60  65  70  75  80  85\nof the following ages, viz.        Yrs.Yrs.Yrs.Yrs.Yrs.Yrs.Yrs.Yrs.\n\nThe average duration of Human\nLife of both sexes collectively\nmay thenceforward be assumed at\na maximum of[2]                     23  19  16  13  11   8   6   3\n\nBy how many weeks does the\naverage duration which results\nfrom the most authentic Tables\nat present known fall short of\nthe maximum Term thus assumed?\n\n Among the higher classes of people exclusively.\n\n     Answer.       Name of the\n                     Observer.   Wks. Wks. Wks. Wks. Wks. Wks. Wks. Wks.\nIn England\u2014\nAmong the Government\nAnnuitants, between\n1775 and 1822\n               John Finlaison.    35    1    7   10   47   11   14   53\n\nAmong the Lives assured\nat the Equitable Office,\nbetween 1760 and 1834\n                Arthur Morgan.   119   83   87   81   96   33   10   27\n\nAmong the Nominees of\nthe Tontine of 1693--\nbetween that year\nand 1775\n               John Finlaison.   269  195  170  141  157  110   90   89\n\nIn France--\nAmong the Nominees of\nthe Tontine of 1693--\nbetween that year and\n1745           M. de Parcieux.   133   88   87   86  118   70   55   65\n\nIn Holland--\nAmong the Public\nAnnuitants, between\n1615 and 1740\n                M. Kersseboom.   186  118  104   75   96   61   48   84\n\nIn regard to the mass of the people.\n\nIn Breslau in Silesia,\nbetween 1700 and 1725,\n                   Dr. Halley.   275  211  181  150  166  100   36  137\n\nIn Sweden,\nbetween 1775\nand 1795,         M. Nicander,\n                and Mr. Milne.   207  161  164  146  156   94   60   60\n\nIn Northampton,\nin England, between\n1735 and 1780,\n                    Dr. Price.   209  178  145  110  125   76   65   85\n\nIn Carlisle,\nin England, between\n1779 and 1787,  Dr. Heysham,\n                and Mr. Milne.    98   74   86   63   94   52   26   46\n\nIn all England and\nWales, between\n1811 and 1831,\n               John Finlaison.   100   59   65   58   87   48   37   49\n\nIn the town of Ostend,\nin Flanders, between\n1805 and 1832,\n               John Finlaison.   276  210  184  146  143   76   50   75\n\nIn all Belgium, between\n1725 and 1832,\n                  M. Quetelet.   183  133  133  117  112   84   50   61\n\n\nLet us trace from this table the differences that have taken place, in\ndifferent countries at different periods, in the duration of life at\na given age. Let us take the age given in the first column, namely,\nfifty. Assuming, then, the highest degree of longevity hitherto\nattained at the age of fifty to be twenty-three years, it appears that,\nbetween the years 1700 and 1725, the mass of the people in Breslau,\nin Silesia, fell short of reaching this period by 275 weeks; the\ninhabitants of the town of Ostend in Flanders, between 1805 and 1832,\nby 276 weeks; the nominees of the tontine of England, between the years\n1693 and 1775, by 269 weeks; the inhabitants of the town of Northampton\nin England, between 1735 and 1780, by 209 weeks; the mass of the people\nin Sweden, between 1775 and 1795, by 207 weeks; the public annuitants\nof Holland, between 1615 and 1740, by 186 weeks; the inhabitants of\nall Belgium, between 1725 and 1832, by 183 weeks; the persons assured\nat the Equitable Office, between 1760 and 1834, by 119 weeks; the\ninhabitants of all England and Wales, between 1811 and 1831, by 100\nweeks; the English government annuitants, between 1775 and 1832, only\nby 35 weeks.\n\nFrom these statements, it appears that, towards the close of the\nseventeenth century, the duration of life in England was considerably\nless than in France: less even than in Holland nearly a century\nearlier. Thus, the nominees of the tontine of France, between the years\n1693 and 1745, at the age of fifty, according to M. De Parcieux, fell\nshort of the maximum longevity by 133 weeks; the public annuitants of\nHolland, seventy-eight years before, namely, between the years 1615 and\n1740, according to M. Kersseboom, fell short of the maximum longevity\nby 186 weeks; whereas, the nominees of the tontine of England, between\nthe years 1693 and 1775, according to Mr. Finlaison, fell short of it\nby 269 weeks; a difference nearly double that of Holland, and quite\ndouble that of France in persons of the corresponding rank in society.\n\nSince that period, surprising changes have taken place in all the\nnations of Europe; but in none has the change been so great as in\nEngland. From that period, when its mortality exceeded that of any\ngreat and prosperous European country, its mortality has been steadily\ndiminishing, and at the present time the value of life is greater in\nEngland than in any other country in the world. Not only has the value\nof life been regularly increasing until it has advanced beyond that of\nany country of which there is any record; but the remarkable fact is\nestablished, that the whole mass of its people now live considerably\nlonger than its higher classes did in the seventeenth and eighteenth\ncenturies. Thus, by inspecting the preceding table, it will be seen\nthat between the years 1693 and 1715, the nominees of the tontine of\nEngland, at the age of fifty, fell short of the maximum longevity\nby 269 weeks; whereas, the mass of the people in all England and\nWales, between the years 1811 and 1831, fell short of it only by 100\nweeks; the entire mass having not only reached the select class, but\nabsolutely advanced beyond it by 169 weeks.\n\nThere cannot be a more interesting and instructive thing than to\nconnect these facts with their causes. This will be attempted in a\nsubsequent part of this work; but the reader will be incomparably\nbetter prepared for the investigation when the processes of life have\nbeen explained, and the influence of physical and moral agents upon\nthem traced. And with this exposition we now proceed.\n\n\n\n\nCHAPTER V.\n\n  Ultimate elements of which the body is composed\u2014Proximate\n  principles\u2014Fluids and solids\u2014Primary\n  tissues\u2014Combinations\u2014Results\u2014Organs, systems,\n  apparatus\u2014Form of the body\u2014Division into head, trunk, and\n  extremities\u2014Structure and function of each\u2014Regions\u2014Seats\n  of the more important internal organs.\n\n\n1. The ultimate elements of which the human body is composed are\nazote, oxygen, and hydrogen (gaseous fluids); and carbon, phosphorus,\ncalcium, sulphur, sodium, potassium, magnesium, and iron (solid\nsubstances). These bodies are called elementary and ultimate, because\nthey are capable of being resolved by no known process into more simple\nsubstances.\n\n2. These elementary bodies unite with each other in different\nproportions, and thus form compound substances. A certain proportion\nof azote uniting with a certain proportion of oxygen, hydrogen, and\ncarbon, forms a compound substance possessing certain properties.\nAnother proportion of azote uniting with a different proportion\nof oxygen, hydrogen, and carbon, forms another compound substance\npossessing properties different from the former. Oxygen, hydrogen, and\ncarbon, uniting in still different proportions without any admixture\nof azote, form a third compound possessing properties different from\neither of the preceding. The compounds thus formed by the primary\ncombinations of the elementary substances with each other are called\nPROXIMATE PRINCIPLES.\n\n3. Each proximate principle constitutes a distinct form of animal\nmatter, of which the most important are named gelatin, albumen, fibrin,\noily or fatty matter, mucus, urea, pichromel, osmazome, resin, and\nsugar.\n\n4. By chemical analysis it is ascertained that all the proximate\nprinciples of the body, however they may differ from each other in\nappearance and in properties, are composed of the same ultimate\nelements. Gelatin, for example, consists (in 100 parts) of azote\n16-988/1000, oxygen 27-207/1000, hydrogen 7-914/1000, carbon\n47-881/1000 parts. The elementary bodies uniting in the above\nproportions form an animal substance, soft, tremulous, solid, soluble\nin water, especially when heated, and on cooling, which may be\nconsidered as its distinctive property, separating from its solution in\nwater into the same solid substance, without undergoing any change in\nits chemical constitution.\n\n5. Again, albumen consists of azote 15-705/1000, oxygen 23-872/1000,\nhydrogen 7-540/1000, carbon 52-888/1000, parts. The elementary bodies\nuniting in these different proportions, there results a second\nproximate principle, an adhesive fluid, transparent, destitute of smell\nand taste, miscible in water, but when subjected to a temperature of\nabout 165\u00b0, converted into a solid substance no longer capable of being\ndissolved in water. This conversion of albumen from a fluid, which is\nits natural state, into a solid, by the application of heat, is called\ncoagulation. It is a process familiar to every one. The white of egg is\nnearly pure albumen, naturally a glary and adhesive fluid: by boiling,\nit is coagulated into a white and firm solid.\n\n6. In like manner, fibrin consists of azote 19-934/1000, oxygen\n19-685/1000, hydrogen 7-021/1000, carbon 53-360/1000 parts, forming\na solid substance of a pale whitish colour and firm consistence, the\npeculiar character of which is its disposition to arrange itself into\nminute threads or fibres.\n\n7. On the other hand, fat or oil, which is a fluid substance of a\nwhitish yellow colour, inodorous, nearly insipid, unctuous, insoluble\nin water and burning with rapidity, consists of a larger proportion of\nhydrogen, a small proportion of oxygen, and a still smaller proportion\nof carbon, without any admixture of azote.\n\n8. From this account of the composition of the proximate principles,\nwhich it is not necessary to extend further, it is manifest that all of\nthem consist of the same ultimate elements, and that they derive their\ndifferent properties from the different proportions in which their\nelements are combined.\n\n9. The ultimate elements that compose the body are never found in a\nseparate or gaseous state, but always in combination in the form of one\nor other of the proximate principles.\n\n10. In like manner, the proximate principles never exist in a distinct\nand pure state, but each is combined with one or more of the others. No\npart consists wholly of pure albumen, gelatin, or mucus, but albumen is\nmixed with gelatin, or both with mucus.\n\n11. Simple or combined, every proximate principle assumes the form\neither of a fluid or of a solid, and hence the most general and obvious\ndivision of the body is into fluids and solids. But the terms fluid\nand solid are relative, not positive; they merely express the fact\nthat some of the substances in the body are soft and liquid compared\nwith others which are fixed and hard; for there is no fluid, however\nthin, which does not hold in solution some solid matter, and no solid,\nhowever dense, which does not contain some fluid.\n\n12. Fluids and solids are essentially the same in nature; they\ndiffer merely in their mode of aggregation; hence the easy and rapid\ntransition from the one to the other which incessantly takes place in\nthe living body, in which no fluid long remains a fluid, and no solid a\nsolid, but the fluid is constantly passing into the solid and the solid\ninto the fluid.\n\n13. The relative proportion of the fluids in the human body is always\nmuch greater than that of the solids; hence its soft consistence and\nrounded form. The excess, according to the lowest estimate, is as 6\nto 1, and according to the highest, as 10 to 1. But the proportion is\nnever constant; it varies according to age and to the state of the\nhealth. The younger the age, the greater the preponderance of the\nfluids. The human embryo, when first perceptible, is almost wholly\nfluid: solid substances are gradually but slowly superadded, and even\nafter birth the preponderance is strictly according to age; for in\nthe infant, the fluids abound more than in the child; in the child,\nmore than in the youth; in the youth, more than in the adolescent; in\nthe adolescent, more than in the adult; and in the adult, more than\nin the aged. Thus, among the changes that take place in the physical\nconstitution of the body in the progress of life, one of the most\nremarkable is the successive increase in the proportion of its solid\nmatter: hence the softness and roundness of the body in youth; its\nhard, unequal, and angular surface in advanced life; its progressively\nincreasing fixedness and immobility in old age, and ultimate inevitable\ndeath.\n\n14. The fluids are not only more abundant than the solids, but they\nare also more important, as they afford the immediate material of the\norganization of the body; the media by which both its composition and\nits decomposition are effected. They bear nourishment to every part,\nand by them are carried out of the system its noxious and useless\nmatter. In the brain they lay down the soft and delicate cerebral\nsubstance; in the bone, the hard and compact osseous matter; and the\nworn-out particles of both are removed by their instrumentality. Every\npart of the body is a laboratory in which complicated and transforming\nchanges go on every instant; the fluids are the materials on which\nthese changes are wrought; chemistry is the agent by which they are\neffected, and life is the governing power under whose control they take\nplace.\n\n15. The fluids, composed principally of water holding solid matter in\nsolution, or in a state of mechanical division, either contribute to\nthe formation of the blood, or constitute the blood, or are derived\nfrom the blood; and after having served some special office in a\nparticular part of the system, are returned to the blood; and according\nto the nature and proportion of the substances they contain, are\neither aqueous, albuminous, mucous, gelatinous, fibrinous, oleaginous,\nresinous, or saline.\n\n16. When the analysis of the different kinds of animal matter that\nenter into the composition of the body has been carried to its ultimate\npoint, it appears to be resolvable into two primitive forms: first, a\nsubstance capable of coagulation, but possessing no determinate figure;\nand secondly, a substance having a determinate figure and consisting of\nrounded particles. The coagulable substance is capable of existing by\nitself; the rounded particles are never found alone, but are invariably\ncombined with coagulated or coagulable matter. Alone or combined with\nthe rounded particles, the coagulable matter forms, when liquid, the\nfluids, when coagulated, the solids.\n\n17. When solid, the coagulable substance is disposed in one of two\nforms, either in that of minute threads or fibres, or in that of minute\nplates or lamin\u00e6; hence every solid of the body is said to be either\nfibrous or laminated. The fibres or lamin\u00e6 are variously interwoven\nand interlaced, so as to form a net-work or mesh; and the interspaces\nbetween the fibres or lamin\u00e6 are commonly denominated areol\u00e6 or cells\n(fig. XVII).\n\n18. This concrete substance, fibrous or laminated, is variously\nmodified either alone or in combination with the rounded particles.\nThese different modifications and combinations constitute different\nkinds of organic substance. When so distinct as obviously to possess a\npeculiar structure and peculiar properties, each of these modifications\nis considered as a separate form of organized matter, and is called a\nPRIMARY TISSUE. Anatomists and physiologists have been at great pains\nto discriminate and classify these primary tissues; for it is found\nthat when employed in the composition of the body, each preserves its\npeculiar structure and properties wherever placed, however combined,\nand to whatever purpose applied, undergoing only such modification\nas its local connexions and specific uses render indispensable.\nConsidering every substance employed in the construction of the body,\nnot very obviously alike, as a distinct form of organized matter, these\nprimary tissues may be said to consist of five, namely, the membranous,\nthe cartilaginous, the osseous, the muscular, and the nervous.\n\n19. The first primary tissue is the peculiar substance termed MEMBRANE.\nIt has been already stated (16) that one of the ultimate forms of\nanimal matter is a coagulable substance, becoming concrete or solid\nunder the process of coagulation. The commencement of organization\nseems to be the arrangement of this concrete matter into straight\nthready lines, at first so small as to be imperceptible to the naked\neye. Vast numbers of these threads successively uniting, at length\nform a single thread of sufficient magnitude to be visible, but still\nsmaller than the finest thread of the silkworm. If the length of these\nthreads be greater than their breadth, they are called fibres; if,\non the contrary, their breadth exceed their length, they are termed\nplates or lamin\u00e6. By the approximation of these fibres or plates in\nevery possible direction, and by their accumulation, combination, and\ncondensation, is constituted the simplest form of organized substance,\nthe primary tissue called membrane.\n\n20. Membrane once formed is extensively employed in the composition\nof the body: it is indeed the material principally used in producing,\ncovering, containing, protecting, and fixing every other component\npart of it. It forms the main bulk of the cartilaginous tissue; it\nreceives into its cells the earthy matter on which depend the strength\nand hardness of the osseous tissue; it composes the canals or sheaths\nin which are deposited the delicate substance of the muscular, and the\nstill more tender pulp of the nervous tissue; it gives an external\ncovering to the entire body; it lines all its internal surfaces; it\nenvelopes all internal organs; it enters largely as a component element\ninto the substance of every organ of every kind; it almost wholly\nconstitutes all the internal pouches and sacs, such as the stomach, the\nintestines, the bladder; and all tubes and vessels, such as arteries,\nveins, and lymphatics; it furnishes the common substance in which\nall the parts of the body are, as it were, packed; it fills up the\ninterstices between them; it fixes them in their several situations; it\nconnects them all together; in a word, it forms the basis upon which\nthe other parts are superinduced; or rather the mould into which their\nparticles are deposited; so that were it possible to remove every other\nkind of matter, and to leave this primary tissue unaltered in figure\nand undiminished in bulk, the general form and outline of the body, as\nwell as the form and outline of all its individual parts, would remain\nunchanged.\n\n21. The properties which belong to membrane are cohesion, flexibility,\nextensibility, and elasticity. By its property of cohesion, the several\nparts of the body are held together; by its combined properties of\ncohesion, flexibility, and extensibility, the body in general is\nrendered strong, light, and yielding, while particular parts of it\nare made capable of free motion. But elasticity, that property by\nwhich parts removed from their situation in the necessary actions of\nlife are restored to their natural position, may be regarded as its\nspecific property. The varied purposes accomplished in the economy\nby the property of elasticity will be apparent as we advance in our\nsubject. Meantime, it will suffice to observe that it is indispensable\nto the action of the artery in the function of the circulation; to the\naction of the thorax in the function of respiration; to the action of\nthe joints in the function of locomotion: in a word, to the working\nof the entire mechanism by which motion of every kind and degree\nis effected. All these properties are physical, not vital; vital\nproperties do belong even to this primary form of animal matter; but\nthey are comparatively obscure. In the tissue with which organization\ncommences, and which is the least removed from an inorganic substance,\nthe properties that are prominent and essential are merely physical.\n\n22. By chemical analysis, membrane is found to contain but a small\nproportion of azote, the peculiar element of animal matter. Its\nproximate principles are gelatin, albumen, and mucus. In infancy and\nyouth, gelatin is the most abundant ingredient; at a more advanced\nperiod, albumen predominates[3]. Gelatin differs from albumen in\ncontaining a less proportion of azote and a greater proportion of\noxygen; on both accounts it must be regarded as less animalized. Thus\nanimalization bears a certain relation to organization. The simplest\nanimal tissue is the least animalized, and the least of all at the\nearliest period of life. Not only are the physical and mental powers\nless developed in the young than in the adult, but the very chemical\ncomposition of the primary tissue of which the body is constructed is\nless characteristic of the perfect animal.\n\n23. Membrane exists under several distinct forms; a knowledge of the\npeculiarities of which will materially assist us in understanding the\ncomposition of the body. The simplest form of membrane, and that which\nis conceived to constitute the original structure from which all the\nothers art produced, is termed the _cellular_. When in thin slices,\n_cellular membrane_ appears as a semi-transparent and colourless\nsubstance; when examined in thicker masses, it is of a whitish or\ngreyish colour. It consists of minute threads, which cross each other\nin every possible direction, leaving spaces between them, and thus\nforming a mesh or net-work (fig. XVII.), not unlike the spider's web.\nThe term cells, given to these interspaces, is employed rather in a\nfigurative sense than as the expression of the fact; for there are no\nsuch distinct partitions as the term cell implies. The best conception\nthat can be formed of the arrangement of the component parts of\nthis structure is, to suppose a substance consisting of an infinite\nnumber of slender thready lines crossing each other in every possible\ndirection (fig. XVII.). The interspaces between these lines during\nlife, and in the state of health, are filled with a thin exhalation of\nan aqueous nature, a vapour rather than a fluid, rendering and keeping\nthe tissue always moist. This vapour consists of the thinner part of\nthe blood, poured into these interstitial spaces by a process hereafter\nto be described, termed secretion. When occupying those spaces, it\nmakes no long abode within them, but is speedily removed by the process\nof absorption. In health, these two operations exactly equal each\nother; but if any cause arise to disturb the equilibrium, the vapour\naccumulates, condenses and forms an aqueous fluid, which distends the\ncells and gravitates to the most depending parts. Slightly organized\nas this tissue is, and indistinct as its vita functions may be, it\nis obvious that it must be the seat of at least two vital functions,\nsecretion and absorption.\n\n[Illustration: Fig. XVII.\n\nA single film of the cellular tissue lifted up and slightly distended.]\n\n24. It is certain that the interspaces or cells of this membrane have\nno determinate form or size, that they communicate freely with each\nother, and that this communication extends over the whole body; for if\na limb which has been infiltrated be frozen, a thousand small icicles\nwill be formed, assuming the shape of the containing cells, some of\nwhich are found to be circular and others cylindrical, and so on. If\nair or water escape into any particular part of the body, it is often\neffused over the whole extent of it, and butchers are observed to\ninflate animals by making a puncture in some part where the cellular\ntissue is loose, and from this one aperture the air is forced to the\nmost distant parts of the body.\n\n25. Cellular membrane, variously modified and disposed, forms the\nmain bulk of all the other solid parts of the body, constituting\ntheir common envelope and bond of union, and filling up all their\ninterstices. It is dense or loose, coarse or fine, according to its\nsituation and office. Wherever it is subject to pressure, it is dense\nand firm, as in the palm of the hand and the sole of the foot; around\nthe internal organs it is more loose and delicate, and it becomes finer\nand finer as it divides and subdivides, in order to envelope the soft\nand tender structures of the body.\n\n[Illustration: Fig. XVIII.\n\nA portion of cellular tissue, very highly magnified, showing the\nstrings of globules of which its ultimate fibres are by some supposed\nto consist.]\n\n26. According to some who have carefully examined with the microscope\nits component threads, they consist of minute particles of a globular\nfigure (fig. XVIII.); other microscopical observers regard the cellular\nthreads as coagulated or condensed animal substance, perfectly\namorphous (without form).\n\n27. Every part of this tissue is penetrated by arteries, veins,\nabsorbents, and nerves, endowing it with properties truly vital, though\nin a less degree than any of the other primary tissues; and varied and\nimportant as the uses are which it serves in the economy, the most\nmanifest, though certainly not the only ones, are those which depend\nupon its physical properties of cohesion, flexibility, extensibility,\nand elasticity.\n\n[Illustration: Fig. XIX. 1, A portion of adipose tissue; 2, minute bags\ncontaining the fat; 3, a cluster of the bags, separated and suspended.]\n\n28. The tissue which contains the fat, termed the _adipose_, is\nthe second form of membrane; it is obviously a modification of the\ncellular, from which it differs both in the magnitude of its fibres,\nwhence it constitutes a tougher and coarser web, and in their\narrangement; for it is so disposed as to form distinct bags in which\nthe fat is contained. Adipose tissue consists of rounded packets,\nseparated from each other by furrows (fig. XIX. 2, 2); each packet\nis composed of small spheroidal particles (fig. XIX. 2, 2); each\nparticle is again divisible into still smaller grains, which, on minute\ninspection, present the appearance of vesicles filled with the adipose\nmatter (fig. XIX. 3).\n\n29. The cells of the cellular tissue, as has been shown (24), are\ncontinuous over the whole body; but each adipose vesicle is a distinct\nbag, having no communication whatever with any other (fig. XIX. 2, 2).\nThe cellular tissue is universally diffused; but the adipose is placed\nonly in particular parts of the body; principally beneath the skin, and\nmore especially between the skin and the abdominal muscles, and around\nsome of the organs contained in the chest and abdomen, as the heart,\nthe kidneys, the mesentery, and the omenta. In most of these situations\nsome portion of it is generally found, whatever be the degree of\nleanness to which the body may be reduced; while in the cranium, the\nbrain, the eye, the ear, the nose, and several other organs, there is\nnone, whatever be the degree of corpulency. The uses of the fat, which\nare various, will be stated hereafter.\n\n30. The third form of membrane is termed the\n\n_serous_. Like the adipose, _serous membrane_ is a modification of\nthe cellular, and, like it also, it is limited in its situation to\nparticular parts of the body, that is, to its three great cavities,\nnamely, the head, the chest, and the abdomen. To the two latter it\naffords an internal lining, and to all the organs contained in all\nthe three cavities, it affords a covering. By its external surface it\nis united to the wall of the cavity or the substance of the organ it\ninvests; by its internal surface it is free and unattached; whence this\nsurface is in contact only with itself, forming a close cavity or shut\nsac, having no communication with the external air. Smooth and polished\n(fig. XX.), it is rendered moist by a fluid which is supposed to be\nexhaled in a gaseous state from the serum of the blood; and from this\nserous fluid the membrane derives its name.\n\n[Illustration: Fig. XX.\n\nA portion of intestine, showing its external surface or serous coat.]\n\n31. Though thin, serous membrane is dense, compact, and of great\nstrength in proportion to its bulk: it is extensible and elastic;\nextensible, for it expands with the dilatation of the chest in\ninspiration; elastic, for it contracts with the diminished size\nof the chest in expiration. In like manner, it stretches with the\nenlargement of the stomach during a hearty meal, and contracts as\nthe stomach gradually diminishes on emptying itself of its contents.\nIt is furnished with no blood-vessels large enough to admit the\ncolouring matter of the blood; but it is supplied with a great number\nof the colourless vessels termed exhalents, with the vessels termed\nabsorbents, and with a few nerves. It indicates no vital properties,\nbut those which are common to the simple form of the primary tissue.\nIts specific uses are to afford a lining to the internal cavities; to\nfurnish a covering to the internal organs; by its polished and smooth\nsurface, to allow a free motion of those organs on each other, and by\nthe moisture with which it is lubricated, to prevent them from adhering\ntogether, however closely, or for however long a period they may be in\ncontact.\n\n32. The fourth form of membrane, the _fibrous_, named from the obvious\narrangement of its component parts, consists of longitudinal fibres,\nlarge enough to be visible to the naked eye, placed parallel to each\nother, and closely united. Sometimes these fibres are combined in such\na manner as to form a continuous and extended surface, constituting\na thin, smooth, dense, and strong membrane, such as that which lines\nthe external surface of bones termed PERIOSTEUM, or the internal\nsurface of the skull (dura mater). At other times, they form a firm and\ntough expansion (aponeurosis) which descends between certain muscles,\nseparating them from each other, and affording a fixed point for the\norigin or insertion of neighbouring muscles; or which is stretched\nover muscles, and sometimes over even an entire limb, in order to\nconfine the muscles firmly in their situation, and to aid and direct\ntheir action (fig. XXVII.). Fibrous membrane also constitutes the\ncompact, strong, tough, and flexible bands used for tying parts firmly\ntogether, termed LIGAMENTS, principally employed in connecting the\nbones with each other, and particularly about the joints; and lastly,\nfibrous membrane forms the rounded white cords in which muscles often\nterminate, called TENDONS (fig. XXV., XXVI.), the principal use of\nwhich is to connect the muscles with the bones, and to serve as cords\nor ropes to transmit the action of the muscle to a distant point, in\nthe accomplishment of which purposes their operation appears to be\nentirely mechanical.\n\n33. The fifth form of membrane, the _mucous_ (fig. XXI.), derives its\nname from the peculiar fluid with which its surface is covered, called\nmucus, and which is secreted by numerous minute glands, imbedded in\nthe substance of the membrane. As serous membrane forms a shut sac,\ncompletely excluding the air, mucous membrane, on the contrary, lines\nthe various cavities which are exposed to the air, such as the mouth,\nthe nostrils, the wind-pipe, the gullet, the stomach, the intestines,\nthe urinary organs, and the uterine system. Its internal surface, or\nthat by which it is attached to the passages it lines, is smooth and\ndense; its external surface, or that which is exposed to the contact\nof the air, is soft and pulpy, like the pile of velvet (fig. XXI.). It\nbears a considerable resemblance to the external surface of the rind of\nthe ripe peach.\n\n[Illustration: Fig. XXI.\n\nA portion of the stomach, showing its internal surface or mucous coat.]\n\nUnlike all the other tissues of this class, the mucous membranes are\nthe immediate seat of some of the most important functions of the\neconomy; in the lung, of respiration; in the stomach, of digestion; in\none part of the intestine, of chylification; in another, of excretion;\nwhile in the mouth and nose, they are the seat of the animal functions\nof taste and smell; and they are highly organized in accordance with\nthe importance of the functions they perform.\n\n34. The last form of membrane which it is necessary to our present\npurpose to particularize, is that which constitutes the external\ncovering of the body, and which is called the _skin_. The skin is\neverywhere directly continuous with the mucous membranes that line the\ninternal passages, and its structure is perfectly analogous. Both the\nexternal and the internal surface of the body may be said therefore to\nbe covered by a continuous membrane, possessing essentially the same\norganization, and almost identically the same chemical composition.\nThe skin is an organ which performs exceedingly varied and important\nfunctions in the economy, to the understanding of which it is necessary\nto have a clear conception of its structure; some further account of it\nwill therefore be required; but this will be more advantageously given\nwhen the offices it serves are explained.\n\n[Illustration: Fig. XXII. Portions of cartilage, seen in section.]\n\n35. Such is the structure, and such are the properties, of the\nfirst distinct form of organized matter. The second primary tissue,\ntermed the CARTILAGINOUS (fig. XXII.), is a substance intermediate\nbetween membrane and bone. The nature of its organization is not\nclearly ascertained. By some anatomists, it is regarded as a uniform\nand homogeneous substance, like firm jelly, without fibres, plates,\nor cells; others state that they have been able to detect in it\nlongitudinal fibres, interlaced by other fibres in an oblique and\ntransverse direction, but without determinate order. All are agreed\nthat it is without visible vessels or nerves: not that it is supposed\nto be destitute of them, but that they are so minute as to elude\nobservation. Its manifest properties are wholly mechanical. It is\ndense, strong, inextensible, flexible, and highly elastic. It is\nchiefly by its property of elasticity that it accomplishes the various\npurposes it serves in the economy. It is placed at the extremities of\nbones, especially about the joints, where, by its smooth surface, it\nfacilitates motion, and, by its yielding nature, prevents the shock or\njar which would be produced were the same kind and degree of motion\neffected by a rigid and inflexible substance. Where a certain degree\nof strength with a considerable degree of flexibility are required, it\nsupplies the place of bone, as in the spinal column, the ribs and the\nlarynx.\n\n[Illustration: Fig. XXIII.\n\nMembranous portion of bone; the osseous portion being so completely\nremoved, that the bone is capable of being tied in a knot.]\n\n36. The third distinct form of organized matter is termed the\nOSSEOUS tissue. Bone is composed of two distinct substances, an animal\nand an earthy matter: the former organic, the latter inorganic. The\nanimal or organic matter is analogous both in its nature and in its\narrangement to cellular tissue; the earthy or inorganic matter consists\nof phosphoric acid combined with lime, forming phosphate of lime. The\ncellular tissue is aggregated into plates or lamin\u00e6, which are placed\none upon another, leaving between them interspaces or cells, in which\nis deposited the earthy matter (phosphate of lime). If a bone, for\nexample, the bone called the radius, one of the bones of the fore-arm,\nbe immersed in diluted sulphuric, nitric, muriatic, or acetic acid, it\nretains its original bulk and shape; it loses, however, a considerable\nportion of its weight, while it becomes so soft and pliable, that it\nmay be tied in a knot (fig. XXIII.). In this case, its earthy matter\nis removed by the agency of the acid, and is held in solution in the\nfluid; what remains is membranous matter (cellular tissue). If the\nsame bone be placed in a charcoal fire, and the heat be gradually\nraised to whiteness, it appears on cooling as white as chalk; it is\nextremely brittle; it has lost much of its weight, yet its bulk and\nshape continue but little changed. In this case, the membraneous matter\nis wholly consumed by the fire, while the earth is left unchanged (fig.\nXXIV.). Every constituent atom of bone consists, then, essentially\nof animal and earthy matter intimately combined. A little more than\none-third part consists of animal matter (albumen), the remaining\ntwo-thirds consist of earthy matter (phosphate of lime); other saline\nsubstances, as the fluate of lime and the phosphate of magnesia, are\nalso found in minute quantity, but they are not peculiar to bone.\n\n[Illustration: Fig. XXIV.\n\nEarthy portion of bone.]\n\n37. In general, the osseous tissue is placed in the interior of the\nbody. Even when bone approaches the surface, it is always covered\nby soft parts. It is supplied with but few blood-vessels, with\nstill fewer nerves, with no absorbents large enough to be visible,\nso that though it be truly alive, yet its vital properties are not\ngreatly developed. The arrangement of its component particles is\nhighly curious; the structure, the disposition, and the connexion of\nindividual bones afford striking examples of mechanism, and accomplish\nmost important uses in the economy; but those uses are dependent\nrather upon mechanical than vital properties. The chief uses of bone\nare\u2014 1. By its hardness and firmness to afford a support to the soft\nparts, forming pillars to which the more delicate and flexible organs\nare attached and kept in their relative positions. 2. To defend the\nsoft and tender organs by forming a case in which they are lodged and\nprotected, as that formed by the bones of the cranium for the lodgment\nand protection of the brain (fig. XLVII.); by the bones of the spinal\ncolumn for the lodgment and protection of the spinal cord (fig.\nXLVIII.); by the bones of the thorax (fig. LIX.), for the lodgment and\nprotection of the lungs, the heart, and the great vessels connected\nwith it (fig. LIX.). 3. By affording fixed points for the action of the\nmuscles, and by assisting in the formation of joints to aid the muscles\nin accomplishing the function of locomotion.\n\n38. All the primary tissues which have now been considered consist of\nprecisely the same proximate principles. Albumen is the basis of them\nall; with the albumen is always mixed more or less gelatin, together\nwith a minute quantity of saline substance: to the osseous tissue is\nsuperadded a large proportion of earthy matter. With the exception\nof the mucous, the organization of all these tissues is simple;\ntheir vital properties are low in kind and in degree; their decided\nproperties are physical, and the uses they serve in the economy are\nalmost wholly mechanical.\n\n[Illustration: Fig. XXV.\n\nPortion of a muscle; showing (_a_) the muscular fibres and their\nparallel direction; and (_b_) the termination of the fibres in tendon.]\n\n39. But we next come to a tissue widely different in every one of\nthose circumstances, a tissue consisting of a new kind of animal\nmatter, and endowed with a property not only peculiar to itself,\nbut proper to living substance, and characteristic of a high degree\nof vital power. MUSCULAR TISSUE, the fourth distinct form of animal\nmatter, commonly known under the name of flesh, is a substance\nresembling no other in nature. It consists of a soft and pulpy\nsubstance, having little cohesive power, arranged into fibres which\nare distinctly visible to the naked eye, and which are disposed in a\nregular and uniform manner, being placed close and parallel to each\nother (fig. XXV.). These fibres are every where pretty uniformly the\nsame in shape, size, and general appearance, being delicate, soft,\nflattened, and though consisting only of a tender pulp, still solid\n(fig. XXV.). When examined under the microscope, fibres, which to the\nnaked eye appear to be single threads, are seen to divide successively\ninto smaller threads, the minutest or the ultimate division not\nexceeding, as is supposed, the 40,000th part of an inch in diameter. On\nthe other hand, the fibres which are large enough to be visible to the\nnaked eye, are obviously aggregated into bundles of different magnitude\nin different muscles, but always of the same uniform size in the same\nmuscle (fig. XXV.).\n\n[Illustration: Fig. XXVI.\n\nTwo portions of muscle; one of which, _a_, is covered with membrane;\nthe other, _b_, is uncovered; _c_, the muscular fibres terminating in\ntendon.]\n\n40. The ultimate thread, or the minutest division of which the\nmuscular fibre is susceptible, is called a filament; the smallest\nthread which can be distinguished by the naked eye is termed a fibre\n(fig. XXVI.); and the bundle which is formed by the union of fibres\nis denominated a fasciculus. The proper muscular substance is thus\narranged into three distinct forms progressively increasing in\nsize,\u2014the filament, the fibre, and the fasciculus. The filament, the\nfibre, the fasciculus, as well as the muscle itself, formed by the\naggregation of fasciculi, is each inclosed in its own distinct sheath\nof cellular membrane (fig. XXVI. _a_).\n\n[Illustration: Fig. XXVII.\n\nPortion of a muscle enclosed in a sheath of fascia or aponeurosis.]\n\n41. The composition of the ultimate filament has been very carefully\nexamined by many distinguished physiologists with microscopes of high\nmagnifying power. Under some of these microscopes the filament appears\nto consist of a series of rounded particles or globules of the same\nsize as the particles of the blood when deprived of their colouring\nmatter, so that it looks like a string of pearls (fig. XXVIII.), each\nglobule being commonly stated to be about the 2000th part of an inch\nin diameter. But it is now pretty generally agreed that this globular\nappearance of the ultimate muscular fibre vanishes under the more\nimproved microscopes of the present day, and, as viewed by the latter,\nappears as a peculiar pulpy substance arranged into threads of extreme\nminuteness, placed close and parallel to each other, intersected by a\ngreat number of delicate lines passing transversely across the muscular\nthreads (fig. XXIX.),\n\n[Illustration: Fig. XXVIII.\n\nUltimate fibres of muscle, very greatly magnified; showing the strings\nof globules of which they are supposed by some to consist.]\n\n42. With the exception of the organs of sense, the muscular tissue is\nmore abundantly supplied with arteries, veins, and nerves, than any\nother substance of the body. Every ultimate thread or filament appears\nto be provided with the ultimate branch of an artery, vein, and nerve.\nThese vessels are seen ramifying on the surface of the delicate web of\nmembrane that incloses the pulp, but cannot be traced into it.\n\n[Illustration: Fig. XXIX.\n\nThe appearance of the ultimate muscular fibres and of their transverse\nlines, as seen under the microscope of Mr. Lister, when the object is\nmagnified 500 diameters.]\n\n43. The proximate principle of which the muscular pulp is composed\nis fibrin. From the pulp, when inclosed in its sheath of membrane,\nalbumen, jelly, various salts, and a peculiar animal extract called\nosmazome, are also obtained; but these substances are probably derived\nfrom the membranous, not the muscular, matter. Fibrin contains a larger\nproportion of azote, the element peculiar to the animal body, and by\nthe possession of which its chemical composition is distinguished from\nthat of the vegetable, than any other animal substance.\n\n[Illustration: Fig. XXX.\n\nPortion of the trunk of a nerve; dividing into branches.]\n\n44. Muscular tissue possesses a slight degree of cohesion, a high\ndegree of flexibility and extensibility, but no degree of elasticity;\nfor although muscle, considered as a compound of muscular substance and\nmembrane, be highly elastic, yet this property is probably altogether\nowing to the membranous matter in which it is enveloped. Its peculiar\nand distinctive property is vital, not physical, and consists in the\npower of diminishing its length, or of contracting or shortening itself\non the application of a stimulus. This property, which is termed\ncontractility, is the great, if not the sole source of motion in the\nbody. Without doubt, elasticity and gravity, under the generating and\ncontrolling powder of contractility, aid in accomplishing various\nkinds of motion. Thus membranes, tendons, ligaments, cartilages, and\nbones, by their physical and mechanical properties, modify, economize,\nfacilitate, concentrate and direct the motive power generated by the\npure muscular substance; but still the only real source of motion in\nthe body is muscular tissue, and the only mode in which motion is\ngenerated is by contractility. This will be more fully understood\nhereafter.\n\n[Illustration: Fig. XXXI.\n\nUltimate fibres of nerve, very highly magnified; showing the strings of\nglobules of which they consist.]\n\n45. The last primary tissue, termed the NERVOUS, is equally distinct\nin nature and peculiar in property. It consists of a soft and pulpy\nmatter, of a brownish white colour (fig. XXX.). According to some,\nthe nervous, like the muscular pulp, is composed of minute globules,\narranged in the same manner like a string of pearls (fig. XXXI.);\naccording to others, it consists of solid elongated threads, of a\ncylindrical form, differing in thickness from that of a hair to the\nfinest fibre of silk. The pulp, whatever its form of aggregation, is\ninclosed in a sheath of delicate cellular tissue. This external or\ncontaining membrane is called the neurilema, or the nerve-coat; the\ninternal or contained substance, the proper nervous matter, is termed\nthe nerve-string. The nerve-string, enveloped in its nerve-coat,\nconstitutes the nervous filament. As in the muscle, so in the nerve,\nmany filaments unite to form a fibre, many fibres to form a fasciculus,\nand many fasciculi to form the large cord termed a nerve. Moreover,\nas in the muscle, so in the nerve, the filament, the fibre, the\nfasciculus, the nervous cord itself, are each enveloped in its own\ndistinct sheath of cellular membrane; but the arrangement of the\nnervous fibres differs from that of the muscular in this, that though\nthe nervous fibres are placed in juxtaposition, yet they do not,\nlike the muscular, maintain through their entire course a parallel\ndisposition, but cross and penetrate each other, so as to form an\nintimate interlacement (fig. XXXII.).\n\n[Illustration: Fig. XXXII.\n\nNervous fibres, deprived of their neurilema and unravelled, showing the\nsmaller threads, or filaments, of which the fibres consist.]\n\n46. The nervous pulp is at least as liberally supplied with\nblood-vessels as the muscular; the vessels are spread out upon the\nnerve-coat, in which they divide into innumerable branches of extreme\nminuteness, the distribution of which is so perfect, that there is\nnot a particle of nervous matter which is not supplied both with an\narterial and a venous vessel. Hence the neurilema is not merely a\nsheath containing and protecting the nervous pulp, but it affords an\nextended mechanical surface for sustaining the arterial vessels, from\nwhich the pulp is probably secreted, and certainly nourished.\n\n47. Albumen, in conjunction with a peculiar fatty matter, constitutes\nthe chief proximate principles of which the nervous tissue is composed.\nTo these are added a small proportion of the animal substance termed\nosmazome, a minute quantity of phosphorus, some salts, and a very large\nproportion of water; for out of one hundred parts of nervous substance,\nwater constitutes as much as eighty. Its peculiar vital property is\nsensibility; and as all motion depends on the contractility of the\nmuscular fibre, so all sensation depends on the sensibility of the\nnervous substance.\n\n48. Such are the primary tissues, or the several kinds of organized\nmatter of which the body is composed; and from this account it is\nobvious that they consist of three only\u2014namely, the concrete matter\nforming the basis of membrane, the pulpy matter forming the proper\nmuscular substance, and the pulpy matter forming the proper nervous\nsubstance. Of these three kinds of animal matter the component parts of\nthe body consist. In combining to form the different structures, these\nprimary substances are intermixed and arranged in a great variety of\nmodes; and from these combinations and arrangements result either an\norgan, a system, or an apparatus.\n\n49. As filaments unite to form fibres, and fibres to form tissues, so\ntissues unite to form organs: that is, bodies having a determinate\nsize and figure, and capable of performing specific actions. The\ncellular, the muscular, and the nervous tissues are not organs;\nmembranes, muscles, and nerves are organs. The tissue, the simple\nanimal substance, is merely one of the elements of which the organ\nis composed; the organ is compounded of several of those simple\nsubstances, arranged in a determinate manner, and moulded into a given\nshape, and so constituting a specific instrument. The basis of the\nmuscle is muscular tissue; but to this are added, invariably, membrane,\noften tendon, and always vessels and nerves. It is this combination\nthat forms the specific instrument called a muscle, and that renders it\ncapable of performing its specific action. And every such combination,\nwith its appropriate endowment, constitutes an organ.\n\n50. Organs are arranged into groups or classes, according as they\npossess an analogous structure, and perform an analogous function; and\nthis assemblage constitutes a SYSTEM. All the muscles of the body,\nfor example, whatever their size, form, situation, or use, have an\nanalogous structure, and perform an analogous function, and hence are\nclassed together under the name of the muscular system. All the bones,\nwhatever their figure, magnitude, density, position, or office, are\nanalogous in structure and function; and hence are classed together\nunder the name of the osseous system. For the same reason, all the\ncartilages, ligaments, vessels and nerves, form respectively the\ncartilaginous, ligamentous, vascular and nervous systems.\n\n51. An APPARATUS, on the contrary, is an assemblage of organs, it\nmay be differing widely from each other in structure, and exercising\nvarious and even opposite functions; but all nevertheless concurring\nin the production of some common object. The apparatus of nutrition\nconsists of the organs of mastication, deglutition, digestion,\nabsorption, and assimilation. Among the individual organs which concur\nin carrying on these functions may be reckoned the lips, the teeth,\nthe tongue, the muscles connected with the jaws, the gullet, the\nstomach, the duodenum, the small intestines, the pancreas, the liver,\nthe lacteal vessels, the mesenteric glands, and the lungs. Many of\nthese organs have no similarity in structure, and few have any thing\nanalogous in function; yet all concur, each in its appropriate mode and\nmeasure, to the conversion of the aliment into blood. In the apparatus\nof respiration, in that of circulation, of secretion, of excretion;\nin the apparatus of locomotion, in the apparatus of sensation, and\nmore especially in the apparatus of the specific sensations,\u2014vision,\nhearing, smell, taste, touch, organs are combined which have nothing\nin common but their concurrence in the production of a common end:\nbut this concurrence is the principle of their combination; and the\nindividual organs having this conjoint operation, taken together,\nconstitute an apparatus.\n\n52. A clear idea may now be affixed to the terms structure and\norganization. Structure may be considered as synonymous with\narrangement; the disposition of parts in a determinate order; that\nwhich is constructed or built up in a definite mode, according to a\ndeterminate plan. The arrangement of the threads of the cellular web\ninto areol\u00e6 or cells; the combination of the primary threads into\nfibres or lamin\u00e6; the disposition of the muscular pulp into filaments,\nplaced parallel to each other; the investment of the filaments in\nmembraneous sheaths; the combination of the filaments, included in\ntheir sheaths, into fibres; the aggregation of fibres into fasciculi;\nand the analogous arrangement and combination of the nervous pulp,\nare examples of structure. But when those structures are applied to\nparticular uses; when they are so combined and disposed as to form\na peculiar instrument, endowed with a specific function; when the\ncellular fibres, for example, are so arranged as to make a thin, dense,\nand expanded tissue; when to this tissue are added blood-vessels,\nabsorbents, and nerves; when, in a word, a membrane is constructed,\nan organ is formed; when, in like manner, to the muscular and the\nnervous fibres, arranged and moulded in the requisite mode, are added\nblood-vessels, absorbents, and nerves, other organs are constructed\ncapable of performing specific functions: and this is organization\u2014the\nbuilding up of organs\u2014the combination of definite structures\ninto special instruments. Structure is the preparatory process of\norganization; the one is the mere arrangement of the material; the\nother is the appropriation of the prepared material to a specific use.\n\n53. The term organization is employed in reference both to the\ncomponent parts of the body, and to the body considered as a whole. We\nspeak of an organized substance and of an organized body. An organized\nsubstance is one in which there is not only a definite arrangement\nof its component parts (structure), but in which the particular\narrangement is such as to fit it for accomplishing some special\nuse. Every organized substance is therefore essentially a special\norgan; limited in its object it may be, and perhaps only conducive\nto some further object; but still its distinctive character is, that\nit has a peculiar structure, fitting it for the accomplishment of\nsome appropriate purpose. On the other hand, an organized body is a\ncongeries of organs\u2014the aggregate of the individual organs. Attention\nwas directed in the early part of this work to one peculiar and\nessential character, by which such an organized is distinguished from\nan unorganized body. Between the individual parts of the organized body\nthere is so close a relation, that no one of them can be removed or\ninjured, or in any manner affected without a corresponding affection of\nthe whole. The action of the heart cannot cease without the cessation\nof the action of the lung; nor that of the lung without that of the\nbrain; nor that of the brain without that of the stomach; in a word,\nthere is no organ in whatever distant nook of the system it be placed,\nor however apparently insignificant its function, that is not necessary\nto the perfection of the whole. But into whatever number of portions an\nunorganized body may be divided, each portion retains the properties of\nthe mass, and constitutes in itself a perfect existence; there being\nno relation between its individual parts, excepting that of physical\nattraction: on the contrary, each component part of an organized body,\nbeing endowed with some appropriate and specific power, on the exercise\nof which the powers of all the other parts are more or less dependent,\nthe whole must necessarily suffer if but one part fail.\n\n54. From the whole, then, we see that the human body is a congeries of\norgans; that those organs are constructed of a few simple tissues; and\nthat all its parts, numerous, diversified, and complex as they are, are\ncomposed of but three primary forms of animal matter variously modified\nand combined.\n\n[Illustration: Fig. XXXIII.\n\nMuscles of the back and shoulders; showing their symmetrical\ndisposition.]\n\n55. But though by the analysis of its component parts, this machine,\nso complex in its construction, and so wonderfully endowed, may be\nreduced to this state of simplicity; and although this analytical view\nof it be highly useful in enabling us to form a clear conception of the\nnature of its composition; yet it is only by considering its individual\nparts such as they actually are, and by studying their situation,\nconnexion, structure, and action, that we can understand it as a whole,\nand apply our knowledge of it to any practical use.\n\n56. Viewing then the human body as a complicated whole, as a congeries\nof organs made up of various combinations of simple tissues, it may\nbe observed, in reference to its external configuration, that it is\nrounded. This rounded form is principally owing to the large proportion\nof fluids which enter into its composition. The roundness of the face,\nlimbs, and entire surface of the child, are in striking contrast to\nthe unequal and irregular surface of the old man, whose humours are\ncomparatively very much smaller in quantity.\n\n57. The length of the human body exceeds its breadth and thickness;\nthe degree of the excess varying at different periods of life, and\naccording to the peculiar constitution of the individual. In the\nextremities, the bones, muscles, vessels, and nerves, are especially\ndistinguished by their length.\n\n[Illustration: Fig. XXXIV.\n\nFront view of the skeleton. 1. the head; 2. the trunk; 3. the superior\nextremities; 4. the inferior extremities.]\n\n[Illustration: Fig. XXXV.\n\nBack view of the skeleton. 1. the head; 2. the trunk; 3. the superior\nextremities; 4. the inferior extremities.]\n\n58. The form of the human body is symmetrical, that is, it is\ncapable of being divided into two lateral and corresponding halves.\nSuppose a median line to pass from the vertex of the head through the\ncentre of the spinal column (fig. XXXIV. 1, 2); if the body be well\nformed, it will be divided by this line into two exactly equal and\ncorresponding portions (fig. XXXV. 1). This symmetrical disposition\nof the body is not confined to its external configuration. It is\ntrue of many of the internal organs; but principally, as has been\nalready stated, of those that belong to the animal life. The brain and\nthe spinal cord are divisible into two exactly equal halves (figs.\nXLVIII. _d_, and XLIX. 1, 2, 3); the organs of sense are double and\nsymmetrical: the muscles of one side of the body exactly correspond to\nthose of the other (fig. XXXIII.); the two hands and arms and the two\nlower extremities are alike (figs. XXXIV., XXXV.); but for the most\npart, the organs of the organic life, the stomach, the intestines, the\nliver, the spleen, for example, are single, and not symmetrical.\n\n59. The human body is divided into three great portions, the head, the\ntrunk, and the extremities (figs. XXXIV. and XXXV. 1, 2, 3, 4).\n\n60. By the HEAD is meant all that part of the body which is placed\nabove the first bone of the neck (fig. XXXIV. 1). It is of a spheroidal\nfigure, broader and deeper behind than before, somewhat like an egg in\nshape, with the broad end behind; it is flattened at its sides (figs.\nXXXV. 1, and XXXVI. 2, 4). Its peculiar figure renders it at once\nstronger and more capacious than it could have been had it possessed\nany other form. It is supported by its base on the spinal column, to\nwhich it is attached by the peculiar structure termed a joint (fig.\nXXXIV.), and fastened by ligaments of exceeding strength.\n\n61. The head contains the central organ of the nervous system; the\norgans of the senses, with the exception of that of touch; and the\norgans of mastication. It comprehends the cranium and the face. Both\nare composed partly of soft parts, as the teguments, namely, skin, fat,\n&c., and muscles; and partly of bones.\n\n[Illustration: Fig. XXXVI.\n\n1. Frontal bone; 2. parietal bone; 3. occipital bone; 4. temporal bone;\n5. nasal bone; 6. malar bone; 7. superior maxillary bone; 8. inferior\nmaxillary bone.]\n\n[Illustration: Fig. XXXVII.\n\nBones of the skull, separated; front view. 1. Frontal bone; 2. portions\nof the parietal bones; 3. malar or cheek bones; 4. nasal bones; 5.\nsuperior maxillary or bones of the upper jaw; 6. the vomer; 7. the\ninferior maxillary or bone of the lower jaw.]\n\n[Illustration: Fig. XXXVIII.\n\nBones of the skull separated; side view. 1. Frontal bone; 2. parietal\nbone; 3. occipital bone; 4. temporal bone; 5. nasal bone; 6. malar\nbone; 7. superior maxillary bone; 8. the unguis; 9. the inferior\nmaxillary bone.]\n\n[Illustration: Fig. XXXIX.\n\nBones forming the base of the skull; viewed from the inside. 1.\nOccipital bone; 2. temporal bones; 3. sphenoid bone; 4. ethmoid bone;\n5. superior maxillary bones, or bones of the upper jaw; 6. malar or\ncheek bones; 7. foramen magnum.]\n\n62. The bones of the cranium are eight in number, six of which are\nproper to the cranium, and two are common to it and to the face. The\nsix bones proper to the cranium are the frontal (fig. XXXVII. 1), the\ntwo parietal (fig. XXXVI. 2), the two temporal (fig. XXXVIII. 4), and\nthe occipital (fig. XXXVIII. 3); the two common to the cranium and face\nare the ethmoidal (fig. XXXIX. 4), and the sphenoidal (fig. XXXIX.\n3). The frontal bone forms the entire forepart of the vault (fig.\nXXXVII. 1); the two parietal form the upper and middle part of it (fig.\nXXXVIII. 2); the two temporal form the lower part of the sides (fig.\nXXXVIII. 4); the occipital forms the whole hinder part, together with a\nportion of the base (figs. XXXVIII. 3, XXXVI. 3, XXXIX. 1); while the\nethmoidal forms the forepart, and the sphenoidal the middle part of the\nbase (fig. XXXIX. 3, 4).\n\n[Illustration: Fig. XL.\n\n2 1\n\nPortions of the bones of the cranium; showing the corresponding\ninequalities in their margins: which margins, when in apposition,\nconstitute the mode of union termed suture. 1. External surface of the\nbone; 2. internal surface.]\n\n[Illustration: Fig. XLI.\n\n1\n\nFig. XLII.\n\n2\n\n1. Side view of the adult skull, showing the several bones united by\nsuture; 2. side view of the f\u0153tal skull, showing the bones imperfectly\nossified, separated to some extent from each other, the interspace\nbeing occupied by membrane. The small size of the face compared with\nthat of the cranium is strikingly apparent.]\n\n63. These bones are firmly united together. The union of bones is\ntechnically called an _articulation_ or _joint_. All joints are either\nimmoveable or moveable. The union of the bones of the cranium affords\nan example of an immoveable articulation. Prominences and indentations,\nlike the teeth of a saw, are formed in the margins of the contiguous\nbones (figs. XXXVIII. and XL.). At these inequalities of surface, which\nare exactly adapted to each other (figs. XXXVIII. and XL.), the two\nbones are in immediate apposition in such a manner as to preclude the\npossibility of motion, and even to render the separation extremely\ndifficult. This mode of articulation is termed a _suture_. There are\ncertain advantages in constructing the cranium of several distinct\nbones, and in uniting them in this peculiar mode. 1. The walls of the\nvault are stronger than they could have been had they been formed of a\nsingle piece. 2. In the f\u0153tus, the bones are at some distance from each\nother (fig. XLII.); at birth, they yield and overlap one another; and\nin this manner they conduce to the security and ease of that event. 3.\nMinute vessels pass abundantly and securely through the interstices of\nthe sutures to and from the interior of the cranium; in this manner,\na free communication is established between the vessels within and\nwithout this cavity. 4. It is probable that the shock produced by\nexternal violence is diminished in consequence of the interruption of\nthe vibration occasioned by the suture; it is certain that fracture is\nprevented by it from extending as far as it would do in one continued\nbony substance.\n\n[Illustration: Fig. XLIII.\n\nSection of the skull. 1. Cavity of the cranium occupied by the brain;\n2. cut edge of the bones of the cranium, showing the two tables of\ncompact bone and the intervening spongy texture called diplo\u00eb.]\n\n64. The vault of the cranium forms a cavity which contains the\nbrain (fig. XLIII. and XLVIII.) The size of this cavity is invariably\nproportioned to that of the organ it lodges and protects. The form and\nmagnitude of the cavity, and consequently the shape and size of the\ncranium, depend upon the brain, and not of the brain upon the cranium.\nThe soft parts model and adapt to themselves the hard, and not the hard\nthe soft. The formation of the brain in the f\u0153tus is anterior to that\nof the case which ultimately contains it; and the hard bone is moulded\nupon the soft pulp, not the pulp upon the bone. At every period of\nlife, on the inner surface of the cranium there are visible impressions\nmade by the convolutions of the brain, and the ramifications of the\narteries (figs. XXXIX. 1, 2, and XL. 2), and on its external surface\nare depressions occasioned by the action of the external muscles. Nor\ndoes the modifying power of the brain over the bones of the cranium\nterminate at birth. The formation of bone, always a slow process,\nis never completed until the child has attained its third or fourth\nyear, and often not until a much later period. At this tender age, the\nbones, which in advanced life are hard and rigid, are comparatively\nsoft and yielding, and consequently more readily receive and retain\nthe impression of the convolutions and of the other projecting parts\nof the brain, by which they are sometimes so deeply marked, that an\nattentive examination of the inner surface of the cranium is of itself\nsufficient to determine not only that some part, but to indicate the\nvery part of the brain which has been preternaturally active. At this\ntender age, pressure, internal or external, general or partial, may\nreadily change the form of the cranium. If, by a particular posture,\nthe head of a child be unequally balanced on the spine, the brain will\npress more on that side of the cranium than on the other; the organ\nwill expand in the direction to which it inclines; that portion of it\nwill become preternaturally developed, and consequently the balance of\nits functions will be disturbed. An awkward way of standing or sitting,\nperhaps contracted inadvertently and kept up by habit; a wry neck; any\ncause that keeps the head constantly inclined to one side, may produce\nthis result, examples of which and of its consequences will be given\nhereafter.\n\n65. Tracing them from without inwards we see, then, that the various\ncoverings afforded to the brain, the central organ of the animal life,\nseated in its vaulted cavity, are: 1. The tegument, consisting of the\nskin and of cellular and adipose membrane. 2. Beneath the tegument,\nmuscles, in the forepart and at the vertex, comparatively slender and\ndelicate; at the sides and posteriorly, thick, strong, and powerful\n(fig. XLIV.). 3. Beneath the muscles, a thin but dense membrane, termed\nthe pericranium, lining the external surface of the cranial bones. 4.\nBeneath the pericranium, the bony substance of the cranium, consisting\nof two firm and hard bony plates, with a spongy, bony structure, called\ndiplo\u00eb, interposed between them (fig. XLIII. 2). 5. Immediately in\ncontact with the inner surface of the bony substance of the cranium,\nand forming its internal lining, the dense and strong membrane, called\nthe _dura mater_, not only affording a general covering to the brain,\nbut sending firm partitions between individual portions of it (fig.\nXLVIII. _c._). 6. A serous membrane lining the internal surface of\nthe dura mater, and reflected over the entire surface of the brain,\ntermed the arachnoid tunic. 7. A thin and delicate membrane in\nimmediate contact with the substance of the brain, descending between\nall its convolutions, lining all its cavities and enveloping all its\nfibres, called the pia mater. 8. An aqueous fluid, contained between\nthe arachnoid membrane and the pia mater. Skin, muscle, pericranium,\nbone, dura mater, arachnoid membrane, pia mater, and aqueous fluid,\nsuperimposed one upon another, form, then, the covering and defence of\nthe brain; so great is the care taken to protect this soft and tender\nsubstance.\n\n66. The bones of the _face_ consist of fourteen, namely, the two\nsuperior maxillary or jaw-bones (fig. XXXVII. 5), the two malar or\ncheek bones (fig. XXXVII. 3), the two nasal bones (fig. XXXVII. 4),\nthe two palate bones, the two ossa unguis (fig. XXXVIII. 8), the two\ninferior turbinated bones, the vomer (fig. XXXVII. 6), and the inferior\nmaxilla or the lower jaw (fig. XXXVII. 7.) This irregular pile of bones\nis divided into the superior and inferior maxilla or jaws; the superior\nmaxilla being the upper and immoveable portion of the face; the\ninferior maxilla being the lower and moveable portion of it. Besides\nthese bones, the face contains thirty-two teeth, sixteen in each\njaw. The bones of the upper jaw are united together by sutures, and\nthe union is so firm, that they have no motion but what they possess\nin common with the cranium. The lower jaw is united by a distinct\narticulation with the cranium (figs. XXXIV. and XXXV.).\n\n67. Besides the bones and the teguments, the face contains a number of\nmuscles, which for the most part are small and delicate (fig. XLIV.),\ntogether with a considerable portion of adipose matter; while, as has\nbeen stated, the face and head together contain all the senses, with\nthe exception of that of touch, which is diffused, more or less, over\nthe entire surface of the body.\n\n[Illustration: Fig. XLIV.\n\nMuscles of the face.]\n\n68. The second great division of the body, termed the TRUNK, extends\nfrom the first bone of the neck to that called the pubis in front, and\nto the lower end of the coccyx behind (fig. XXXIV. 2). It is subdivided\ninto the thorax, the abdomen, and the pelvis (fig. XLV.).\n\n69. The _thorax_ or _chest_ extends above from the first bone of\nthe neck, by which it is connected with the head, to the diaphragm\nbelow, by which it is divided from the abdomen (figs. XLV. and LXI.).\nIt consists partly of muscles and partly of bones; the muscular and\nthe osseous portions being in nearly equal proportions. Both together\nform the walls of a cavity in which are placed the central organs of\ncirculation and respiration (fig. LX. 2, 5). The chief boundaries of\nthe cavity of the thorax before, behind, and at the sides, are osseous\n(fig. XLV.); being formed before, by the sternum or breast-bone (fig.\nXLV. 6); behind, by the spinal column or back bone (fig. XLV. 2, 4);\nand at the sides, by the ribs (fig. XLV. 7). Below, the boundary is\nmuscular, being formed by the diaphragm (fig. LXI. 2), while above the\nthorax is so much contracted (fig. XLV.), that there is merely a space\nleft for the passage of certain parts which will be noticed immediately.\n\n70. The figure of the thorax is that of a cone, the apex being above\n(fig. XLV.), through the aperture of which pass the tubes that lead\nto the lungs and stomach, and the great blood-vessels that go to and\nfrom the heart (fig. LX.). The base of the cone is slanting, and is\nconsiderably shorter before than behind, like an oblique section of the\ncone (fig. XLV.).\n\n71. The osseous portion of the walls of the thorax is formed behind by\nthe spinal column, a range of bones common indeed to all the divisions\nof the trunk; for it constitutes alike the posterior boundary of the\nthorax, abdomen, and pelvis (fig. XLV. 2, 4, 6). It is composed of\nthirty distinct bones, twenty-four of which are separate and moveable\non one another, and on this account are called true vertebr\u00e6 (fig. XLV.\n2, 4); the other five, though separate at an early period of life, are\nsubsequently united into a single solid piece, called the sacrum (fig.\nXLV. 5). The bones composing this solid piece, as they admit of no\nmotion on each other, are called false vertebr\u00e6 (fig. XLV. 5). To the\nextremity of the sacrum is attached the last bone of the series, termed\nthe coccyx (fig. XXXV.).\n\n72. From above downwards, that is, from the first bone of the neck to\nthe first bone of the sacrum, the separate bones forming the column\nprogressively increase in size; for this column is the chief support\nof the weight of the head and trunk, and this weight is progressively\naugmenting to this point (fig. XLV. 2, 4). From the sacrum to the\ncoccyx, the bones successively diminish in size, until, at the\nextremity of the coccyx, they come to a point (fig. XXXV.). The spinal\ncolumn may therefore be said to consist of two pyramids united at their\nbase (fig. XLV. 4, 5). The superior pyramid is equal in length to about\none third of the height of the body, and it is this portion of the\ncolumn only that is moveable.\n\n73. The two surfaces of the spinal column, the anterior and the\nposterior, present a striking contrast (figs. XXXIV. and XXXV.). The\nanterior surface, which in its whole extent is rounded and smooth, is\nbroad in the region of the neck, narrow in the region of the back, and\nagain broad in the region of the loins (fig. XLV. 2, 4.). It presents\nthree curvatures (fig. XLV. 2, 4); the convexity of that of the neck\nbeing forwards, that of the back backwards, and that of the loins again\nforwards (fig. XLV. 2, 4).\n\n74. From the posterior surface of the column, which is every where\nirregular and rough, spring, along the median line, in regular series,\nstrong, sharp, and pointed projections of bone (fig. XXXV.), which\nfrom being sharp and pointed, like elongated spines, are called\nspinous processes, and have given name to the whole chain of bones.\nThese processes afford fixed points for the action of powerful\nmuscles. Extending the whole length of the column, from the base of\nthe skull to the sacrum, on each side of the spinous processes, are\ndeep excavations, which are filled up with the powerful muscles that\nmaintain the trunk of the body erect.\n\n75. From the lateral surfaces of the column likewise spring short but\nstrong projections of bone, termed transverse processes, which also\ngive attachment to powerful muscles (fig. XLVI.).\n\n[Illustration: Fig. XLV.\n\nBones of the trunk. 1. Spinal column; 2. the seven cervical vertebr\u00e6;\n3. the twelve dorsal vertebr\u00e6; 4. the five lumbar vertebr\u00e6; 5. the\nsacrum; 6. the sternum; 7. the true ribs; 8. the false ribs; 9. the\nclavicle; 10. the scapula; 11. the ilium; 12. the ischium; 13. the\npubes; 14. the acetabulum; 15. the brim of the pelvis.]\n\n76. The separate bones of the series have a kind of turning motion on\neach other; hence each is called a vertebra, and the name of vertebral\ncolumn is often given to the entire series, as well as that of spinal\ncolumn. That portion of the column which forms the neck consists of\nseven distinct bones, called cervical vertebr\u00e6 (fig. XLV. 2); that\nportion which forms the back consists of twelve, called dorsal vertebr\u00e6\n(fig. XLV. 3); that portion which forms the loins consists of five,\ncalled lumbar vertebr\u00e6 (fig. XLV. 4). Between each of these classes of\nvertebr\u00e6 there are specific differences, but they need not be described\nhere: all that is necessary to the present purpose is an account of the\nstructure which is common to every vertebra.\n\n77. By inspecting fig. XLVI. 1, it will be seen that the upper and\nunder edges of each vertebra consist of a ring of bone, of a firm\nand compact texture, rendering what may be called the body of the\nvertebra exceedingly strong (fig. XLVI. 3). This ring of bone forms a\nsuperficial depression (fig. XLVI. 2), for the reception of a peculiar\nsubstance, immediately to be described, which is interposed between\neach vertebra (fig. XLVII. 2).\n\n78. The anterior surface of the body of the vertebra is convex (fig.\nXLVI. 3); its posterior surface is concave (fig. XLVI. 4); from the\nposterior surface springs a bony arch (figs. XLVI. 5 and LIII. 1),\nwhich, together with the posterior concavity, forms an aperture of\nconsiderable magnitude (fig. XLVI. 6), a portion of the canal for the\npassage of the spinal cord (figs. XLVII. 3, and XLIX. 3).\n\n[Illustration: Fig. XLVI.\n\nView of some of the vertebr\u00e6, which by their union form the spinal\ncolumn.\n\n_a._ A vertebra of the neck; _b._ a vertebra of the back; a vertebra of\nthe loins.\n\n1. Ring of compact bone forming, 3, the body of the vertebra; 2.\nsuperficial depression for the reception of the intervertebral\ncartilage; 3. anterior surface of the body of the vertebra; 4.\nposterior surface; 5. bony arch; 6. opening for the passage of the\nspinal cord; 7. opening for the passage of the spinal nerves; 8.\narticulating processes by which the vertebr\u00e6 are joined to each other;\n9. two dorsal vertebr\u00e6 united, showing the arrangement of, 10, the\nspinous processes; 11. a portion of a rib articulated with the side of\nthe vertebra.]\n\n79. Both the upper and under edges of the arch form a notch (fig. XLVI.\n7.), which, together with a corresponding notch in the contiguous\nvertebra, completes another aperture rounder and smaller than the\nformer, but still of considerable size (fig. XLVI. 7.), the passage of\nthe spinal nerves (fig. XLVII. 3).\n\n80. From both the upper and under sides of the arch proceed two short\nbut strong projections of bone (fig. XLVI. 8.), termed the articulating\nprocesses, because it is chiefly by these processes that the vertebr\u00e6\nare connected together. From the beginning to the end of the series,\nthe two upper processes of the one vertebra are united with the two\nlower processes of the vertebra immediately above it (fig. XLVI. 9),\nand around the edges of all the articulating processes are visible\nrough lines, which mark the places to which the articulating ligaments\nare attached.\n\n81. No vertebra, except the first, rests immediately upon its\ncontiguous vertebra (fig. XLV. 2, 4). Each is separated from its fellow\nby a substance of a peculiar nature interposed between them, termed the\nintervertebral substance (figs. XLVII. 2, and L. 2). This substance\npartakes partly of the nature of cartilage, and partly of that of\nligament. It is composed of concentric plates, formed of oblique fibres\nwhich intersect each other in every direction. This substance, for\nabout a quarter of an inch from its circumference towards its centre,\nis tough, strong, and unyielding; then it becomes softer, and is\nmanifestly elastic; and so it continues until it approaches the centre,\nwhen it becomes pulpy, and is again inelastic. The exterior tough and\nunyielding matter is for the firmness of the connexion of the several\nvertebr\u00e6 with each other; the interior softer and elastic matter is for\nthe easy play of the vertebr\u00e6 upon each other; the one for security,\nthe other for pliancy. And the adjustment of the one to the other is\nsuch as to combine these properties in a perfect, manner. The quantity\nof the unyielding substance is not so great as to produce rigidity;\nthe quantity of the elastic substance is not so great as to occasion\ninsecurity. The firm union of its solid matter renders the entire\ncolumn strong; the aggregate elasticity of its softer substance renders\nit springy.\n\n[Illustration: Fig. XLVII.\n\n1. One of the Lumbar vertebr\u00e6. 2. Intervertebral substance. 3. A\nportion of the spinal cord in its canal.]\n\n82. The column is not constructed in such a manner as to admit of an\nequal degree of motion in every part of it. Every thing is contrived\nto give to that portion which belongs to the neck freedom of motion,\nand, on the contrary, to render that portion which belongs to the back\ncomparatively fixed. In the neck the mechanism of the articulating\nprocesses is such as to admit of an equal degree of sliding motion\nforwards, backwards, and from side to side, together with a turning\nmotion of one bone upon another; at the same time, the intervertebral\nsubstance between the several vertebr\u00e6 is thick. In consequence of this\nmechanism, we can touch the breast with the chin, the back with the\nhind head, and the shoulders with the ear, while we can make the head\ndescribe more than a semicircle. But, in the back, the articulating\nprocesses are so connected as to prevent the possibility of any motion,\neither forwards or backwards, or any turning of one vertebra upon\nanother, while the intervertebral substance is comparatively thin (fig.\nXLV. 2, 4). That portion of the column which belongs to the back is\nintended to afford a fixed support for the ribs, a support which is\nindispensable to their action in the function of respiration. In the\nloins, the articulating processes are so connected as to admit of a\nconsiderable degree of motion in the horizontal direction, and from\nside to side, and the intervertebral substance here progressively\nincreases in thickness to the point at which the upper portion of the\ncolumn is united to the sacrum (fig. XLV. 2, 4), where the degree of\nmotion is extensive.\n\n83. The canal for the spinal cord, formed partly by the concavity in\nthe posterior surface of the vertebra, and partly by the arch that\nsprings from it (fig. XLVI. 6.), is lined by a continuation of the\ndense and strong membrane that constitutes the internal periosteum\nof the cranium, the dura mater (fig. XLVIII. _c_), which, passing\nout of the opening in the occipital bone, called the foramen magnum\n(figs. XXXIX. 7, and XLIX. 3), affords a smooth covering to the canal\nthroughout its whole extent.\n\n[Illustration: Fig. XLVIII.\n\n_a._ The scalp, turned down.\n\n_b._ The cut edge of the bones of the skull.\n\n_c._ The external strong membrane of the brain (Dura Mater) suspended\nby a hook.\n\n_d._ The left hemisphere of the brain, showing its convolutions.\n\n_e._ The superior edge of the right hemisphere.\n\n_f._ The fissure between the two hemispheres.]\n\n\n[Illustration: Fig. XLIX.\n\n1. Hemispheres of the brain proper, or cerebrum; 2. hemispheres of the\nsmaller brain, or cerebellum; 3. spinal cord continuous with the brain,\nand the spinal nerves proceeding from it on each side.]\n\n84. The spinal cord itself, continuous with the substance of the\nbrain, passes also out of the cranium through the foramen magnum into\nthe spinal canal (fig. XLIX. 3), enveloped in the delicate membranes\nthat cover it, and surrounded by the aqueous fluid contained between\nthose membranes. The size of the spinal canal, accurately adapted\nto that of the spinal cord, which it lodges and protects, is of\nconsiderable size, and of a triangular shape in its cervical portion\n(fig. XLIX. 3), smaller and rounded in its dorsal portion (fig. XLIX.\n3), and again large and triangular in its lumbar portion (fig. XLIX. 3).\n\n85. The spinal column performs several different, and apparently\nincompatible, offices.\n\nFirst, it affords a support and buttress to other bones. It sustains\nthe head (fig. XXXIV. 1); it is a buttress to the ribs (fig. XLVI. 7);\nthrough the sternum and ribs it is also a buttress to the superior, and\nthrough the pelvis, to the lower, extremities (fig. XXXIV. 2, 3, 4).\n\nSecondly, it affords a support to powerful muscles, partly to those\nthat maintain the trunk of the body in the erect posture against the\nforce of gravitation, and partly to those that act upon the superior\nand inferior extremities in the varied, energetic, and sometimes\nlong-continued movements they execute.\n\nThirdly, it forms one of the boundaries of the great cavities that\ncontain the chief organs of the organic life. To the support and\nprotection of those organs it is specially adapted; hence the surface\nin immediate contact with them is even and smooth; hence its different\ncurvatures, convexities, and concavities, have all reference to their\naccommodation; hence in the neck it is convex (fig. XLV. 2), in order\nto afford a firm support to the esophagus, the wind-pipe, the aorta,\nand the great trunks of the venous system (fig. LX. 3, 4); in the back\nit is concave, in order to enlarge the space for the dilatation of\nthe lung in the act of inspiration (figs. XLV. 3, and LX. 5); in the\nloins it is convex, in order to sustain and fix the loose and floating\nviscera of the abdomen (figs. XLV. 4, and LX. 6, 7, 8, 9); in the\npelvis it is concave, in order to enlarge the space for lodging the\nnumerous delicate and highly-important organs contained in that cavity\n(fig. XLV. 5).\n\nFourthly, it forms the osseous walls of a canal (figs. XLVI. 6, and\nXLVII. 3) for the lodgment and protection of the soft and tender\nsubstance of the spinal cord, one of the great central masses of the\nnervous system, the seat of the animal life (fig. XLIX. 3).\n\nFifthly, it affords in its osseous walls secure apertures for the\npassage of the spinal nerves (figs. XLVI. 7, and XLIX. 3), by which\nimpressions are transmitted from the organs to the spinal cord and\nbrain, in the function of sensation; and from the spinal cord and brain\nto the organs in the function of volition.\n\n86. For the due performance of these offices, it is indispensable that\nit should be firm, rigid, strong, and yet to a certain extent readily\nflexible in every direction. By what mechanism is it endowed with these\napparently incompatible properties?\n\n87. By means of the ring of compact bone, which forms so large a part\nof its body (fig. XLVI. 1) it is rendered firm, rigid, and strong. By\nmeans of its numerous separate pieces, exactly adjusted to each other,\nand dove-tailed into one another, an increase of strength is gained,\nsuch as it would not have been possible to communicate to a single\nsolid piece. By the same mechanism, some degree of flexibility is also\nobtained; each separate bone yielding to some extent, which, though\nslight in a single bone, becomes considerable in the twenty-four.\n\n88. But the flexibility required is much greater than could be\nobtained by this expedient alone. A rigid and immoveable pile of bones,\nin the position of the spinal column, on which all the other parts of\nthe body rest, and to which they are directly or indirectly attached,\nwould necessarily have rendered all its movements stiff and mechanical;\nand every movement of every kind impossible, but in a given direction.\nThat the movements of the body may be easy, free, and varied; that it\nmay be possible to bring into play new and complex combinations of\nmotion at any instant, with the rapidity of the changes of thought,\nat the command of the impulses of feeling, it is indispensable that\nthe spinal column be flexible in every direction, forwards, backwards,\nand at the sides: it is equally indispensable that it be thus capable\nof yielding, without injuring the spinal cord; without injuring the\nspinal nerves; without injuring the thoracic and abdominal viscera; and\nwithout injuring the muscles of the trunk and extremities. The degree\nin which it possesses this power of flexibility, and the extent to\nwhich, by the cultivation of it, it is sometimes actually brought, is\nexemplified in the positions and contortions of the posture-master and\nthe tumbler. It is acquired by means of the intervertebral substance,\nthe compressible and elastic matter interposed between the several\nvertebr\u00e6. So compressible is this substance, that the human body is\nhalf an inch shorter in the evening than in the morning, having lost\nby the exertions of the day so much of its stature; yet, so elastic is\nthis matter, that the stature lost during the day is regained by the\nrepose of the night. The weight of the body pressing in all directions\nupon the spinal column; muscles, bones, cartilages, ligaments,\nmembranes, with all their vessels and all the fluids contained in\nthem; the weight of all these component parts of the head, trunk, and\nextremities, pressing, without the cessation of an instant, during all\nthe hours of vigilance, upon the intervertebral substance, compresses\nit; but this weight, being taken off during the night, by the recumbent\nposture of the body, the intervertebral substance, in consequence of\nits elasticity, regains its original bulk, and of course the spinal\ncolumn its original length.\n\n89. But the flexibility acquired through the combined properties of\ncompressibility and elasticity is exceedingly increased by the action\nof the pulpy and inelastic matter in the centre of the intervertebral\nsubstance; this matter serving as a pivot to the vertebr\u00e6, facilitating\ntheir motion on each other. Its effect has been compared to that of\na bladder partly filled with water, placed between two trenchers; in\nthis case, the approximation of the circumference of the two trenchers\non one side, would instantly displace a portion of the water on that\nside, which would occupy the increasing space on the other, with the\neffect of facilitating the change, in every possible direction, of\nthe position of the two trenchers in relation to each other. To this\neffect, however, it is indispensable that the matter immediately around\nthis central pivot should be, not like itself, rigid and unyielding,\nbut compressible and elastic. It is an interesting fact, that since\nthis illustration was suggested, it has been discovered that this\nvery arrangement is actually adopted in the animal body. In certain\nanimals, in the very centre of their intervertebral substance, there\nhas been actually found a bag of water, with a substance immediately\nsurrounding the bag, so exceedingly elastic, that when the bag is cut,\nthe fluid contained in it is projected to the height of several feet in\na perpendicular stream.\n\n90. But besides securing freedom and extent of motion, the\nintervertebral substance serves still another purpose, which well\ndeserves attention.\n\nFirmness and strength are indispensable to the fundamental offices\nperformed by the column; and to endow it with these properties, we\nhave seen that the external concentric layers of the intervertebral\nsubstance are exceedingly tough and that they are attached to the\nbodies of the vertebr\u00e6, which are composed of dense and compact bone.\nBut than dense and compact bone, nothing can be conceived better\ncalculated to receive and transmit a shock or jar on the application\nof any degree of force to the column. Yet such force must necessarily\nbe applied to it in every direction, from many points of the body,\nduring almost every moment of the day; and did it actually produce a\ncorresponding shock, the consequence would be fatal: the spinal cord\nand brain would be inevitably killed; for the death of these tender and\ndelicate substances may be produced by a violent jar, although not a\nparticle of the substances themselves be touched. A blow on the head\nmay destroy life instantaneously, by what is termed concussion; that\nis, by the communication of a shock to the brain through the bones of\nthe cranium. The brain is killed; but on careful examination of the\ncerebral substance after death, not the slightest morbid appearance\ncan be detected: death is occasioned merely by the jar. A special\nprovision is made against this evil, in the structure of the bones\nof the cranium, by the interposition between its two compact plates\nof the spongy substance called diplo\u00eb (fig. XLIII. 2); and this is\nsufficient to prevent mischief in ordinary cases. A great degree of\nviolence applied directly to the head is not common: when it occurs\nit is accidental: thousands of people pass through life without ever\nhaving suffered from it on a single occasion: but every hour, in the\nordinary movements of the body, and much more in the violent movements\nwhich it occasionally makes, a degree of force is applied to the spinal\ncolumn, and through it transmitted to the head, such as, did it produce\na proportionate shock, would inevitably and instantly destroy both\nspinal cord and brain. The evil is obviated partly by the elastic, and\npartly by the non elastic properties of the matter interposed between\nthe several layers of compact bone. By means of the elastic property\nof this matter, the head rides upon the summit of the column as upon a\npliant spring, while the canal of the spinal cord remains secure and\nuninvaded. By means of the soft and pulpy portion of this matter, the\nvibrations excited in the compact bone are absorbed point by point as\nthey are produced: as many layers of this soft and pulpy substance, so\nmany points of absorption of the tremors excited in the compact bone;\nso many barriers against the possibility of the transmission of a shock\nto the delicate nervous substance.\n\n91. Alike admirable is the mechanism by which the separate pieces\nof the column are joined together. If but one of the bones were to\nslip off its corresponding bone, or to be displaced in any degree,\nincurable paralysis, followed ultimately by death, or instantaneous\ndeath, would happen; for pressure on the spinal cord in a certain part\nof its course is incompatible with the power of voluntary motion, and\nwith the continuance of life for any protracted term; and in another\npart of its course, with the maintenance of life beyond a few moments.\nTo prevent such consequences, so great is the strength, so perfect the\nattachment, so unconquerable the resistance of that portion of the\nintervertebral substance which surrounds the edge of the bodies of the\nvertebr\u00e6, that it will allow the bone itself to give way rather than\nyield. Yet such is the importance of security to this portion of the\nframe, that it is not trusted to one expedient alone, adequate as that\nmight seem. Besides the intervertebral substance, there is another\ndistinct provision for the articulation of the bodies of the vertebr\u00e6.\nCommencing at the second cervical vertebra, in its fore part, and\nextending the whole length of the column to the sacrum, is a powerful\nligament, composed of numerous distinct longitudinal fibres (fig. L.),\nwhich are particularly expanded over the intervals between the bones\noccupied by the intervertebral substance (figs. L. 1, and LI. 2, 2).\nThis ligament is termed the _common anterior vertebral_, beneath which,\nif it be raised from the intervertebral substance, may be seen small\n_decussating_ fibres, passing from the lower edge of the vertebra\nabove, to the upper edge of the vertebra below (fig. L. 3), from which\ncircumstance these fibres are termed _crucial_.\n\n[Illustration: Fig. L.\n\n1. Common anterior ligament; 2. intervertebral substance. The anterior\nligament is removed to exhibit (3.) the crucial fibres passing over it.]\n\n[Illustration: Fig. LI.\n\n1. Portion of the occipital bone; 2. common anterior ligament.]\n\n92. Corresponding with the ligament on the anterior, is another on\nthe posterior part of the spine (fig. LII. 1), which takes its origin\nfrom the foramen magnum (fig. LII. 1); descends from thence, within the\nvertebral canal, on the posterior surface of the bodies of the vertebra\n(fig. LII. 1), and extends to the sacrum. This ligament is termed the\n_common posterior vertebral_, which, besides adding to the strength of\nthe union of the bodies of the vertebr\u00e6, prevents the column itself\nfrom being bent too much forward.\n\n[Illustration: Fig. LII.\n\n1. Posterior vertebral ligament.]\n\n93. Moreover, the bony arches of the vertebr\u00e6 (fig. LIII. 1) are\nconnected by means of a substance partly ligamentous, and partly\ncartilaginous (fig. LIII. 2), which, while it is extremely elastic, is\ncapable of resisting an extraordinary degree of force.\n\n[Illustration: Fig. LIII.\n\n1. Arches of the vertebr\u00e6 seen from within; 2. ligaments connecting\nthem.]\n\n94. And in the last place, the articular processes form so many\ndistinct joints, each being furnished with all the apparatus of a\nmoveable joint, and thus possessing the ordinary provision for the\narticulation of bones, in addition to the whole of the foregoing\nsecurities.\n\n95. \"In the most extensive motion of which the spinal column is\ncapable, that of flexion, the common anterior ligament is relaxed; the\nfore part of the intervertebral substance is compressed, and its back\npart stretched; while the common posterior ligament is in a state of\nextension. In the _extension_ of the column the state of the ligaments\nis reversed; those which were extended being in their turn relaxed,\nwhile the common anterior vertebral is now put upon the stretch. In the\n_lateral inclination_ of the column, the intervertebral substance is\ncompressed on that side to which the body is bent. In the _rotatory_\nmotion of the column, which is very limited in all the vertebr\u00e6, but\nmore particularly in the dorsal, in consequence of their attachment to\nthe ribs, the intervertebral substance is contorted, as are likewise\nall the ligaments. All the motions of the column are capable of being\naided to a great extent by the motion of the pelvis upon the thighs.\"\n\n96. \"The number and breadth of the attachments of these bones,\"\nsays an accomplished anatomist and surgeon,[4] \"their firm union by\nligament, the strength of their muscles, the very inconsiderable\ndegree of motion which exists between any two of them, and lastly, the\nobliquity of their articular processes, especially in the dorsal and\nlumbar vertebr\u00e6, render dislocation of them, at least in those regions,\nimpossible without fracture; and I much doubt whether dislocation even\nof the cervical vertebr\u00e6 ever occurs without fracture, either through\ntheir bodies or their articular processes. The effects of each of these\naccidents would produce precisely the same injury to the spinal marrow,\nand symptoms of greater or less importance, according to the part of\nthe spinal column that is injured. Death is the immediate consequence\nif the injury be above the third cervical vertebra, the necessary\nparalysis of the parts to which the phrenic and intercostal nerves\nare distributed causing respiration instantly to cease. If the injury\nbe sustained below the fourth cervical vertebra, the diaphragm is\nstill capable of action, and dissolution is protracted. The symptoms,\nin fact, are less violent in proportion as the injury to the spinal\nmarrow is further removed from the brain; but death is the inevitable\nconsequence, and that in every case at no very distant period.\"\n\n97. So the object of the construction of the spinal column being\nto combine extent and freedom of motion with strength, and it being\nnecessary to the accomplishment of this object to build up the column\nof separate pieces of bone, the connecting substances by which the\ndifferent bones are united are constituted and disposed in such a\nmanner as to prove absolutely stronger than the bones themselves. Such\nis the structure of this important portion of the human body considered\nas a piece of mere mechanism; but our conception of its beauty and\nperfection would be most inadequate if we did not bear in mind, that\nwhile the spinal column performs offices so varied and apparently so\nincompatible, it forms an integrant portion of a living machine: it is\nitself alive: every instant, blood-vessels, absorbents and nerves, are\nnourishing, removing, renewing, and animating every part and particle\nof it.\n\n98. The anterior boundary of the thorax is formed by the bone called\nthe sternum, or the breast-bone, which is broad and thick at its upper,\nand thin and elongated at its lower extremity (figs. XLV. 6, and\nLIV.), where it gives attachment to a cartilaginous appendix, which\nbeing pointed and somewhat like a broadsword, is called the ensiform\ncartilage.\n\n[Illustration: Fig. LIV.\n\nAnterior view of the sternum.]\n\n99. Its position is oblique, being near the vertebral column at the\ntop, and distant from it at the bottom (fig. XLV. 6). Its margins\nare thick, and marked by seven depressions, for the reception of the\ncartilages of the seven true ribs (fig. LIV). Its anterior surface is\nimmediately subjacent to the skin, and gives attachment to powerful\nmuscles, which act on the superior extremities: its posterior surface\nis slightly hollowed in order to enlarge the cavity of the thorax (fig.\nLV.).\n\n[Illustration: Fig. LV.\n\nPosterior view of the sternum.]\n\n100. The thorax is bounded at the sides by the ribs, which extend like\nso many arches between the spinal column and the sternum (fig. XLV. 7,\n8). They are in number twenty-four, twelve on each side, of which the\nseven upper are united to the sternum by cartilage, and are called true\nribs (fig. XLV. 7); the cartilages of the remaining five are united\nwith each other and are not attached to the sternum; these are called\nfalse ribs (fig. XLV. 8): all of them are connected behind to the\nspinal column (fig. XXXV.).\n\n101. The ribs successively and considerably increase in length as far\nas the seventh, by which the cavity they encompass is enlarged; from\nthe seventh they successively diminish in length, and the capacity of\nthe corresponding part of the cavity is lessened. The direction of the\nribs from above downwards is oblique (fig. XLV. 7, 8). Their external\nor anterior surface is convex (fig. XLV. 7, 8); their internal or\nposterior surface is concave: by the first their strength is increased;\nby the second the general cavity of the thorax is enlarged (fig. XLV.\n7, 8). Their upper margin is smooth and rounded, and gives attachment\nto a double layer of muscles, called the intercostal, placed in the\nintervals that separate the ribs from each other (fig. LIX.). Along\nthe lower margin is excavated a deep groove, for the lodgment and\nprotection of the intercostal vessels.\n\n102. The ribs are connected with the spinal column chiefly by what is\ntermed the _anterior ligament_ (fig. LVI. 1), which is attached to the\nhead of the rib (fig. LVI.), and which, dividing into three portions\n(fig. LVI. 1), firmly unites every rib to two of the vertebr\u00e6, and\nto the intervertebral substance (fig. LVI. 1). This articulation is\nfortified by a second ligament (fig. LVI. 2), also attached to a head\nof the rib, termed the _interarticular_ (fig. LVI. 2), and by three\nothers, one of which is attached on the fore part, and the two others\nin the back part, to the neck of the rib (fig. LVII. 1).\n\n[Illustration: Fig. LVI.\n\nLigaments connecting the ribs to the spinal column. 1. anterior\nligaments; 2. interarticular ligament; 3. ligaments of the necks of the\nribs.]\n\nThe cartilages of the seven superior ribs are attached to the sternum\nby a double layer of ligamentous fibres, termed the _anterior and the\nposterior ligaments of the sternum_ (fig. LVIII.). So strong are the\nbands which thus attach the ribs to the spinal column and the sternum,\nthat the ribs cannot be dislocated without fracture. \"Such at least is\nthe case in experiments upon the dead body, where, though the rib be\nsubjected to the application of force by means of an instrument best\ncalculated to detach its head from the articulation, yet it is always\nbroken.\"\n\n[Illustration: Fig. LVII.\n\n1, &c. Ligaments connecting the ribs to the vertebr\u00e6 behind.]\n\nWhile thus firmly attached to their points of support, the ligaments,\nwhich fix them, are so disposed as to render the ribs capable of being\nreadily moved upwards and downwards: upwards in inspiration; downwards\nin expiration; and it is by this alternate action that they enlarge and\ndiminish the cavity of the thorax in the function of respiration.\n\n[Illustration: Fig. LVIII.\n\nLigaments joining the cartilages of the ribs to the sternum.]\n\n103. Such are the boundaries of the cavity of the thorax as far as\nits walls are solid. The interspaces between these solid portions at\nthe sides are filled up by muscles, principally by those termed the\nintercostal (fig. LIX.); below, the boundary is formed by the diaphragm\n(fig. LXI. 2); while above, as has been already stated (69), the cavity\nis so contracted as only to leave an opening for the passage of certain\nparts to and from the chest.\n\n[Illustration: Fig. LIX.\n\nA view of the muscles called _Intercostals_, filling up the spaces\nbetween the ribs.]\n\n104. The inner surface of the walls of the thorax, in its whole\nextent, is lined by a serous membrane, exceedingly thin and delicate,\nbut still firm, called the pleura. The same membrane is reflected over\nthe organs of respiration contained in the cavity, so as to give them\nan external coat. The membrane itself is every where continuous, and\nevery where the same, whether it line the containing or the contained\nparts; but it receives a different name as it covers the one or the\nother: that portion of it which lines the walls of the cavity being\ncalled the costal pleura (fig. LXI. _a_), while that which covers the\norgans contained in the cavity is termed the pulmonary pleura (fig. LX.\n5, 1).\n\n105. A fold of each pleura passes directly across the central part\nof the cavity of the thorax; extending from the spinal column to the\nsternum, and dividing the general cavity into two. This portion of the\npleura is called the mediastinum, from its situation in the centre\nof the thorax, and it so completely divides the thoracic cavity into\ntwo, that the organs on one side of the chest have no communication\nwith those of the other; so that there may be extensive disease in one\ncavity (for example, a large accumulation of water,) while the other\nmay be perfectly sound.\n\n106. The main organs contained in the cavity of the thorax are the\nlungs with their air tube; the heart with its great vessels; and the\ntube passing from the mouth to the stomach (fig. LX.).\n\n107. The two lungs occupy the sides of the chest (fig. LX. 5). They\nare completely separated from each other by the membranous partition\njust described, the mediastinum. Between the two folds of the\nmediastinum, namely, in the middle of the chest, but inclining somewhat\nto the left side, is placed the heart, enveloped in another serous\nmembrane, the pericardium (fig. LX. 2, 1).\n\n108. The lungs are moulded to the cavities they fill; whence their\nfigure is conical, the base of the cone being downwards, resting on the\ndiaphragm (fig. LX. 5, _b_); and the apex upwards, towards the neck\n(fig. LX. 5).\n\n109. That surface of each lung which corresponds to the walls of the\nchest is convex in its whole extent (fig. LX. 5); on the contrary, that\nsurface which corresponds to the mediastinum is flattened (fig. LX.\n5). The basis of the lung is concave, adapted to the convexity of the\ndiaphragm on which it rests (fig. LX. 5).\n\n110. The air-vessel of the lungs, termed the bronchus, together with\nthe blood-vessels and nerves, enter the organ at its flattened side,\nnot exactly in the middle, but rather towards the upper and back part.\nThis portion is termed the root of the lung.\n\n111. The lungs are attached to the neck by the trachea (fig. LX. 4),\nthe continuation of which forms the bronchus; to the spinal column by\nthe pleura, and to the heart by the pulmonary vessels (fig. LX. 3,\n_d_): their remaining portion is free and unattached.\n\n112. In the living body, the lungs on each side completely fill the\ncavity of the chest, following passively the movements of its walls,\nand accurately adapting themselves to its size, whether its capacity\nenlarge in inspiration, or diminish in expiration, so that the external\nsurface of the lung (the pulmonary pleura) is always in immediate\ncontact with the lining membrane of the walls of the cavity (the costal\npleura); consequently, during life, there is no cavity, the chest being\nalways completely full.\n\n[Illustration: Fig. LX.\n\n_a._ The cut edges of the ribs, forming the lateral boundaries of the\ncavity of the thorax.\n\n_b._ The diaphragm, forming the inferior boundary of the thorax, and\nthe division between the thorax and the abdomen.\n\n_c._ The cut edges of the abdominal muscles, turned aside, exposing the\ngeneral cavity of the abdomen.\n\n1. The cut edge of the pericardium turned aside.\n\n2. The heart.\n\n3. The great vessels in immediate connexion with the heart.\n\n4. The trachea, or wind-pipe.\n\n5. The lungs.\n\n6. The liver.\n\n7. The stomach.\n\n8. The large intestine.\n\n9. The small intestines.\n\n10. The urinary bladder.]\n\n113. The anterior surface of the pericardium, the bag which envelopes\nthe heart, lies immediately behind the sternum, and the cartilages of\nthe second, third, fourth, and fifth ribs, covered at its sides by the\npleura, and firmly attached below to the diaphragm (fig. LX. 1).\n\n114. Surrounded by its pericardium, within the mediastinum, the heart\nis placed nearly in the centre of the chest, but its direction is\nsomewhat oblique, its apex being directly opposite to the interval\nbetween the fifth and sixth ribs on the left side (fig. LX. 2); while\nits basis is directed upwards, backwards, and towards the right (fig.\nLX. 2). That portion of its surface which is presented to view on\nopening the pericardium is convex (fig. LX. 2); but its opposite\nsurface, namely, that which rests upon the part of the pericardium\nwhich is attached to the diaphragm, is flattened (fig. LX. 1). It is\nfixed in its situation partly by the pericardium and partly by the\ngreat vessels that go to and from it. But under the different states\nof expiration and inspiration, it accompanies, in some degree, the\nmovements of the diaphragm; and in the varied postures of the body,\nthe heart deviates to a certain extent from the exact position here\ndescribed.\n\n115. The second division of the trunk, the _abdomen_, is bounded above\nby the diaphragm (fig. LXI. 2), below by the pelvis (fig. LXI. 3),\nbehind and at the sides by the vertebr\u00e6 and muscles of the loins (fig.\nLXIII.), and before by the abdominal muscles (fig. LXIII. 9).\n\n116. The organ which forms the superior boundary of the abdomen, the\ndiaphragm (midriff), is a circular muscle, placed transversely across\nthe trunk, nearly at its centre (fig. LXI. 2). It forms a vaulted\npartition between the thorax and the abdomen (fig. LXI. 2). All around\nits border it is fleshy (fig. LXI. 2); towards its centre it is\ntendinous (fig. LXI. 2); the surface towards the abdomen is concave\n(fig. LXI. 2); that towards the thorax convex (fig. LXI. 2); while its\nmiddle tendinous portion ascends into the thorax as high as the fourth\nrib (fig. LXI. 2).\n\n[Illustration: Fig. LXI.\n\nView of the diaphragm. 1. Cavity of the thorax; 2. diaphragm separating\nthe cavity of the thorax from that of the abdomen; 3. cavity of the\npelvis.]\n\n117. The diaphragm is perforated by several apertures, for the\ntransmission of tubes and vessels, which pass reciprocally between the\nthorax and abdomen (fig. LXII.).\n\n1. A separate aperture is formed to afford an exit from the thorax\nof the aorta, the common source of the arteries (fig. LXII. 2), and\nan entrance into the thorax of the thoracic duct, the tube that bears\nthe digested aliment to the heart. 2. A little to the left of the\nformer, there is another aperture, through which passes the esophagus\nor gullet (fig. LXII. 3), the tube that conveys the food from the mouth\nto the stomach. 3. On the right side, in the tendinous portion of the\ndiaphragm, very carefully constructed, is a third aperture for the\npassage of the vena cava (fig. LXII. 4), the great vessel that returns\nthe blood to the heart from the lower parts of the body.\n\n[Illustration: Fig. LXII.\n\nView of the diaphragm with the tubes that pass through it. 1. Arch\nof the diaphragm; 2. the trunk of the aorta passing from the chest\ninto the abdomen; 3. the esophagus passing from the chest through the\ndiaphragm to the stomach; 4. the vena cava, the great vein that returns\nthe blood to the heart from the lower parts of the body, passing from\nthe abdomen, into the chest, in its way to the right side of the heart;\n5. 6. muscles that arise in the interior of the trunk and that act upon\nthe thigh; 5. the muscle called psoas; 6. the muscle called iliacus.]\n\n118. The partition formed by the diaphragm between the thorax and\nabdomen, though complete, is moveable; for as the diaphragm descends in\ninspiration and ascends in expiration, it proportionally enlarges or\ndiminishes the cavities between which it is placed; consequently, the\nactual magnitude of these cavities varies every moment, and the size of\nthe one is always in the inverse ratio of that of the other.\n\n119. Between the abdomen and the pelvis there is no separation; one\ncavity is directly continuous with the other (fig. LXI. 3); but along\nthe inner surface of the expanded bones, which form a part of the\nlateral boundary of the abdomen, there is a prominent line, termed\nthe brim of the pelvis (fig. XLV. 15), marking the point at which the\nabdomen is supposed to terminate and the pelvis to commence.\n\n120. Behind and at the sides the walls of the abdomen are completed\npartly by the lumbar portion of the spinal column and partly by the\nlumbar muscles (fig. XLV. 4), and before by the abdominal muscles (fig.\nLXIII. 9).\n\n121. The inner surface of the walls of the abdomen is lined throughout\nby a serous membrane, termed the peritoneum (fig. LXIII.). From the\nwalls of the abdomen, the peritoneum is reflected upon the organs\ncontained in the cavity, and is continued over them so as to form their\nexternal coat. The peritoneum also descends between the several organs,\nconnecting them together, and holding them firmly in their situation;\nand it likewise forms numerous folds, in which are embedded the vessels\nand nerves that supply the organs. It secretes a serous fluid, by\nwhich its own surface and that of the organs it covers is rendered\nmoist, polished, and glistening, and by means of which the organs\nglide smoothly over it, and over one another in the various movements\nof the body, and are in constant contact without growing together. In\nstructure, distribution, and function, the peritoneum is thus perfectly\nanalogous to the pleura.\n\n122. Like the thorax, the abdomen is always completely full. When\nthe diaphragm is in action, it contracts. When the diaphragm is\nin the state of contraction, the abdominal and lumbar muscles are\nin the state of relaxation. By the contraction of the diaphragm,\nthe organs contained in the abdomen are pushed downwards, and the\nanterior and lateral walls of the cavity being at this moment in\na state of relaxation, they readily yield, and, consequently, the\nviscera are protruded forwards and at the sides. But the abdominal\nand lumbar muscles in their turn contract, the diaphragm relaxing;\nand, consequently, the viscera, forced from the front and sides of the\nabdomen, are pushed upwards, together with the diaphragm, into the\ncavity of the thorax. A firm and uniform pressure is thus at all times\nmaintained upon the whole contents of the abdomen: there is an exact\nadaptation of the containing to the contained parts, and of one organ\nto another. No space intervenes either between the walls of the abdomen\nand the organs they enclose, or between one organ and another: so that\nthe term cavity does not denote a void or empty space, but merely the\nextent of the boundary within which the viscera are contained.\n\n123. The contents of the abdomen consist of the organs which belong to\nthe apparatus of digestion, and of those which belong to the apparatus\nof excretion.\n\n124. The organs which belong to the apparatus of digestion are\u20141. The\nstomach (fig. LXIII. 2) 2. The duodenum (fig. LXIII. 4). 3. The jejunum\n(fig. LXIII. 5). 4. The ilium (fig. LXIII. 5). The three last organs\nare called the small intestines, and their office is partly to carry on\nthe digestion of the aliment commenced in the stomach, and partly to\nafford an extended surface for the absorption of the nutriment as it is\nprepared from the aliment. 5. The pancreas (fig. LXIV. 5). 6. The liver\n(fig. LXIV. 2). 7. The spleen (fig. LXIV. 4). The three last organs\ntruly belong to the apparatus of digestion, and their office is to\nco-operate with the stomach and the small intestines in the conversion\nof the aliment into nutriment.\n\n[Illustration: Fig. LXIII.\n\n1. Esophagus; 2. stomach; 3. liver raised, showing its under surface;\n4. duodenum; 5. small intestines; 6. c\u00e6cum; 7. colon; 8. urinary\nbladder; 9. gall bladder; 10. abdominal muscles divided and reflected.]\n\n125. The organs which belong to the apparatus of excretion are\u20141. The\nlarge intestines consisting of the c\u00e6cum (fig. LXIII. 6). 2. The colon\n(fig. LXIII. 7). 3. The rectum (fig. LXIV. 10). It is the office of\nthese organs, which are called the large intestines, to carry out of\nthe system that portion of the alimentary mass which is not converted\ninto nourishment. 4. The kidneys (fig. LXIV. 6), the organs which\nseparate in the form of the urine an excrementitious matter from the\nblood, in order that it may be conveyed out of the system.\n\n[Illustration: Fig. LXIV.\n\nGeneral view of the viscera of the abdomen. 1. Stomach raised; 2. under\nsurface of liver; 3. gall bladder; 4. spleen; 5. pancreas; 6. kidneys;\n7. ureters; 8. urinary bladder; 9. portion of the intestine called\nduodenum; 10. portion of the intestine called rectum; 11. the aorta.]\n\n126. The last division of the trunk, called the pelvis (fig. LXI. 3),\nconsists of a circle of large and firm bones, interposed between the\nlower portion of the trunk and the inferior extremities (fig. XLV.).\nThe bones that compose the circle, distinct in the child, are firmly\nunited in the adult into a single piece; but as the original separation\nbetween each remains manifest, they are always described as separate\nbones. They are the sacrum (fig. XLV. 5), the coccyx (fig. XXXV.), the\nilium (fig. XLV. 11), the ischium (fig. XLV. 12), and the pubis (fig.\nXLV. 13).\n\n127. The sacrum, placed like a wedge between the moveable portion\nof the spinal column and the lower extremities, forms the posterior\nboundary of the pelvis. The figure of this bone is triangular (fig.\nXLV. 5); its anterior surface is concave and smooth, for enlarging the\ncavity of the pelvis and sustaining the organs contained in it (fig.\nXLV. 5); its posterior surface is convex, irregular, and rough (fig.\nXXXV.), giving origin to the great muscles that form the contour of the\nhip, and to the strong muscles of the back and loins that raise the\nspine and maintain the trunk of the body erect.\n\n128. The base or upper part of the sacrum receives the last vertebra\nof the loins on a large and broad surface (fig. XLV. 4), forming a\nmoveable joint; and the degree of motion at this point is greater than\nit is at the higher points of the spinal column. Firmly united at its\nsides with the haunch bones, it admits there of no degree of motion.\n\n129. The coccyx, so named from its resemblance to the beak of the\ncuckoo, when elongated by a succession of additional bones, forms the\ntail in quadrupeds; but in man it is turned inwards to support the\nparts contained in the pelvis, and to contract the lower opening of\nthe cavity. By means of a layer of cartilage, the medium by which this\nbone is connected with the sacrum, it forms a moveable articulation,\ncontinuing moveable in men until the age of twenty-five, and in women\nuntil the age of forty-five; continuing moveable in women thus long, in\norder that by yielding to the force which tends to push it backwards\nduring the period of labour, it may enlarge the lower aperture of the\npelvis, and so facilitate the process of parturition and diminish its\nsuffering.\n\n130. The lateral boundaries of the pelvis are formed by the ilium,\nthe haunch bone (fig. XLV. 11), and by the ischium, the hip bone (fig.\nXLV. 12). The ilium forms the lower part of the abdomen and the upper\npart of the pelvis (fig. XLV. 11); its broad expanded wing supports the\ncontents of the abdomen, and gives attachment to the muscles that form\nthe anterior portion of its walls (figs. XLV. 11, and LXIII. 9); its\nexternal convex surface sustains the powerful muscles that extend the\nthigh; and along its internal surface is the prominent line which marks\nthe brim of the pelvis (fig. XLV. 15), and which divides this cavity\nfrom that of the abdomen.\n\n131. The ischium or hip bone is the lower part of the pelvis (fig.\nXLV. 12); at its undermost portion is a rounded prominence called\nthe tuberosity (fig. XLV. 12), in its natural condition covered with\ncartilage, upon which is superimposed a cushion of fat. It is this part\non which the body is supported in a sitting posture.\n\n132. The pubis or share bone forms the upper and fore part of the\npelvis (fig. XLV. 13), and together with the two former bones,\ncompletes the large and deep socket, termed the acetabulum (fig. XLV.\n14), into which is received the head of the thigh-bone (fig. XXXIV.\n4). The margin of the acetabulum and the greater part of its internal\nsurface is lined with cartilage, so that in its natural condition it is\nmuch deeper than it appears to be when the bones alone remain.\n\n133. The lower aperture of the pelvis, which appears large when all\nthe soft parts are removed, is not really large, for in its natural\nstate it is filled up partly by muscles and partly by ligaments, which\nsustain and protect the pelvic organs, leaving only just space enough\nfor the passage to and from those which have their opening on the\nexternal surface.\n\n134. The cavity of the pelvis, together with all the organs contained\nin it, are lined by a continuation of the membrane that invests the\nabdomen and its contents.\n\n135. The organs contained in the pelvis are the rectum (fig. LXIV. 9),\nwhich is merely the termination of the large intestines, the urinary\nbladder (fig. LXIV. 8), and the internal part of the apparatus of\nreproduction.\n\n136. The large and strong bones of the pelvis not only afford lodgment\nand protection to the tender organs contained in its cavity, but\nsustain the entire weight of the body, the trunk resting on the sacrum\nas on a solid basis (fig. XLV. 5), and the lower extremities being\nsupported in the sockets in which the heads of the thigh-bones play, in\nthe varied movements of locomotion (fig. XXXIV. 4).\n\n137. The last division of the body comprehends the superior and the\ninferior extremities.\n\n138. The superior extremities consist of the shoulder, arm, fore-arm,\nand hand.\n\n139. The soft parts of the SHOULDER are composed chiefly of muscles;\nits bones are two, the scapula or the _blade bone_, and the clavicle or\nthe _collar bone_ (fig. LXV. 2, 4).\n\n[Illustration: Fig. LXV.\n\n1. Sternum; 2. clavicle; 3. ribs; 4. anterior surface of scapula; 5.\ncoracoid process of scapula; 6. acromion process of scapula; 7. margin\nof glenoid cavity of scapula; 8. body of the humerus or bone of the\narm; 9. head of the humerus.]\n\n140. The SCAPULA is placed upon the upper and back part of the thorax,\nand occupies the space from the second to the seventh ribs (fig. LXV. 4)\n\n[Illustration: Fig. LXVI.\n\n1. Posterior surface of scapula; 2. margin of scapula; 3. acromion\nprocess; 4. margin of glenoid cavity; 5. clavicle; 6. body of humerus;\n7. head of humerus.]\n\nUnlike that of any other bone of the body, it is embedded in muscles,\nwithout being attached to any bone of the trunk, excepting at a single\npoint. From the bones of the thorax it is separated by a double layer\nof muscles, on which it is placed as upon a cushion, and over the\nsmooth surface of which it glides. Originally, like the bones of the\nskull, it consisted of two tables of compact bone, with an intermediate\nlayer of spongy bony substance (diplo\u00eb); but, by the pressure of the\nmuscles that act upon it, it gradually grows thinner and thinner,\nuntil, as age advances, it becomes in some parts quite transparent and\nas thin as a sheet of paper.\n\n141. The figure of the scapula is that of an irregular triangle (fig.\nLXVI.). Its anterior surface is concave (fig. LXV. 4), corresponding to\nthe convexity of the ribs (fig. XLV. 7); its posterior surface is very\nirregular (fig. LXVI. 1), being in some parts concave and in others\nconvex, giving origin especially to two large processes (figs. LXV. 5,\nand LXVI. 3); one of which is termed the _acromion_ (fig. LXVI. 3),\nand the other the _coracoid_ process of the scapula (fig. LXV. 5). The\nmargins of the bone, whatever the thinness of some portions of it, are\nalways comparatively thick and strong (fig. LXVI. 2), affording points\nof origin or of insertion to powerful muscles. At what is called the\nanterior angle of the bone there is a shallow oval depression covered\nwith cartilage and deepened by a cartilaginous margin, called the\n_glenoid_ cavity of the scapula (figs. LXV. 7, and LXVI. 4), which\nreceives the head of the humerus or bone of the arm (figs. LXV. 9, and\nLXVI. 7, 6).\n\n142. The clavicle, the second bone of the shoulder, is a long and\nslender bone, of the form of an italic [Illustration], projecting\na little forwards towards its middle, so as to give a slight convexity\nof outline to the top of the chest and the bottom of the neck (fig.\nLXV. 2). It is attached by one extremity to the sternum (fig. LXV. 2)\nand by the other to the scapula (fig. LXV. 2), by moveable joints. The\nnature of an immoveable joint has been explained (63). In the connexion\nof the bones of the trunk, while the main object is to secure firmness\nof attachment, some degree of motion is at the same time obtained (81\net seq.): but the mode in which the several bones of the extremities\nare connected with each other and with the trunk, admits of so great a\ndegree of motion, that these articulations are pre-eminently entitled\nto the name of moveable joints. The component parts of all moveable\njoints are bone, cartilage, synovial membrane, and ligament. The great\ncharacter of a moveable joint is the approximation of two or more\nbones; yet these bony surfaces are never in actual contact, but are\ninvariably separated from each other by cartilage. The cartilage either\ncovers the entire extent of the articulating surface of the bones,\nas in the shoulder-joint, where both the head of the humerus and the\ncavity of the scapula that receives it are enveloped in this substance\n(fig. LXV. 7. 9), or a portion of it is placed between the articulating\nsurfaces of the bones, as in the joint between the clavicle and sternum\n(fig. LXVII. _a_); which, when so placed, is termed an interarticular\ncartilage (fig. LXVII. _a_). By its smooth surface cartilage lessens\nfriction; while by its elasticity it facilitates motion and prevents\nconcussion. Slightly organized cartilage is provided with comparatively\nfew blood-vessels and nerves. Had it been vascular and sensible like\nthe skin and the muscle, the force applied in the movements of the\njoint would have stimulated the blood-vessels to inordinate action, and\nthe sensibility of the nerves would have been the source of constant\npain: every motion of every joint would have been productive of\nsuffering, and have laid the foundation of disease. The facility and\nease of motion obtained by the smoothness, elasticity, and comparative\ninsensibility of cartilage are still further promoted by the fluid\nwhich lubricates it, termed synovia, secreted by a membrane called\nsynovial, which lines the internal surface of the joint, and which\nbears a close resemblance to the serous (30). Synovia is a viscid\nfluid of the consistence of albumen (5). It is to the joint what oil\nis to the wheel, preventing abrasion and facilitating motion; but it\nis formed by the joint itself, at the moment when needed, and in the\nquantity required. The motion of the joint stimulates the synovial\nmembrane to secretion, and hence the greater the degree of motion, the\nlarger the quantity of lubricating fluid that is supplied. The several\nparts of the apparatus of moveable joints are retained in their proper\nposition by ligamentous substance, which, as has been shown (96 and\n97), is oftentimes so strong that it is easier to fracture the bone\nthan to tear the ligament, and in every case the kind and extent of\nmotion possessed by the joint are dependent mainly on the form of\nthe articulatory surfaces of the bones and on the disposition of the\nligaments.\n\n143. In the joint formed by the clavicle and the sternum (fig. LXVII.\n_a_) an interarticular cartilage is placed between the two bones which\nare united, first by a strong fibrous ligament, which envelops them\nas in a capsule (fig. LXVII. 1); by a second ligament, which extends\nfrom the cartilage of the first rib to the clavicle (fig. LXVII. 4),\nby which the attachment of the clavicle to the sternum is materially\nstrengthened; and by a third ligament which passes transversely from\nthe head of one clavicle to that of the other (fig. LXVII. 3). The\njoint thus formed, though so strong and firm that the dislocation of\nit is exceedingly rare, yet admits of some degree of motion in every\ndirection, upwards, downwards, forwards, and backwards; and this\narticulation is the sole point by which the scapula is connected with\nthe trunk, and consequently by which the upper extremity can act, or be\nacted upon, by the rest of the body.\n\n[Illustration: Fig. LXVII.\n\n1. The fibrous capsule of the sternum and clavicle; 2. the same laid\nopen, showing _a_, the interarticular cartilage; 3. the ligament\nconnecting the two clavicles; 4. the ligament joining the clavicle to\nthe first rib; 5. ligaments passing down in front of the sternum.]\n\n144. The scapular extremity of the clavicle (fig. LXVIII. 6) is\nattached to the processes of the scapula (fig. LXVIII. 4. 3) by several\nligaments of great strength (fig. LXVIII. 7, 8, 9). First by very\nstrong fasciculi which pass from the upper surface of the clavicle\nto the acromion of the scapula (fig. LXVIII. 6); and secondly by two\nligaments which unite the clavicle with the coracoid process of the\nscapula (fig. LXVIII. 8, 9). These ligaments are so powerful that they\nresist a force capable of fracturing the clavicle; and they need to be\nthus strong, for the clavicle is a shaft which sustains the scapula,\nand through the scapula the whole of the upper extremity; and the main\nobject of the joint by which these bones are united, is to afford a\nfirm attachment of the scapula to its point of support.\n\n[Illustration: Fig. LXVIII.\n\n1. The clavicle; 2. the anterior part of the scapula; 3. the coracoid\nprocess; 4. the acromion process; 5. the humerus; 6. ligaments binding\nthe scapular end of the clavicle to the acromion; 7. 8. 9. ligaments\npassing from one process of the scapula to the other; 10. the fibrous\ncapsule of the shoulder-joint.]\n\n145. The clavicle serves the following uses: it sustains the upper\nextremity; it connects the upper extremity with the thorax; it prevents\nthe upper extremity from falling forwards upon the thorax; and it\naffords a fixed point for steadying the extremity in the performance of\nits various actions.\n\n146. The glenoid cavity of the scapula (fig. LXV. 7) receives the head\nof the humerus, the bone of the arm (fig. LXV. 9), and the two bones\nbeing united by ligament form the shoulder-joint (fig. LXVIII.). This\njoint is what is termed a ball and socket joint, the peculiarities\nof which are two: first, beyond all others this mode of articulation\nadmits of free and extensive motion; in the present case, there is\nthe utmost freedom of motion in every direction, upwards, downwards,\nbackwards, and forwards. In the second place, this mode of articulation\nadmits of the motion of the limb without that of the body, or of the\nmotion of the body without that of the limb. When at rest, the arm may\nbe moved in almost any direction without disturbing the position of any\nother part of the frame; the manifold advantages of which are obvious.\nOn the other hand, by careful management, very considerable variations\nin the posture of the body may be effected without the communication\nof any degree of motion to the limb; an unspeakable advantage when the\nlimb has sustained injury, or is suffering from disease.\n\n147. It does not seem possible to construct a joint of great strength,\ncapable, at the same time, of the degree of motion possessed by the\njoint of the shoulder. So shallow is the socket of the scapula, and\nso large the head of the humerus, that it seems as if the slightest\nmovement must dislodge it from its cavity (fig. LXVI. 4. 7). For\nsustaining heavy weights or resisting a great amount of pressure,\napplied to it suddenly and in various directions, the arm is obviously\nunfitted. But this is not its office. The superior extremities are the\norgans of apprehension\u2014the instruments by which the mind executes\nthe commands of the will. They do not need the strength required by\nthe organs that sustain the weight of the body and that perform the\nfunction of locomotion; but they do need freedom and extent of motion:\nto this strength may be sacrificed, and so it is; yet what can be\ndone to combine strength with mobility is effected. Large and strong\nprocesses of bone, proceeding as has been shown (141), from the convex\nsurface of the scapula (figs. LXV. and LXVI.), overhang, and to a\nconsiderable extent surround, the head of the arm-bone, especially\nresisting the force that would dislodge it from its socket and drive\nit upwards, inwards, and backwards (fig. LXV.), the directions in\nwhich force is most commonly applied to it. By these processes of bone\nthe joint is greatly strengthened, especially in those directions.\nMoreover, a strong ligament, termed the fibrous capsule (fig. LXVIII.\n10) envelops the joint. This ligament, arising from the neck of\nthe scapula (fig. LXVIII. 10), expands itself in such a manner as\ncompletely to surround the head of the humerus (fig. LXVIII. 10); and\nthen again contracts in order to be inserted into the neck of the bone\n(fig. LXVIII. 10). This ligament is strengthened by the tendons of no\nless than four muscles which are expanded over it, as well as by the\npowerful substance termed fascia which is reflected upon it from both\nthe processes and ligaments of the scapula. In addition to all these\nexpedients for fortifying the joint, it receives a further security\nin the position of the scapula, which is loose and unattached; which\nslides easily over the ribs upon its cushion of flesh; which thus\nobtains, by its facility of yielding, some compensation for its want of\nstrength, eluding the force which it cannot resist.\n\n148. The arm consists of numerous and powerful muscles, and of a\nsingle bone, the humerus, which belongs to the class of bones termed\ncylindrical (185).\n\n149. The upper end of the humerus terminates in a circular head\n(fig. LXV. 9), which is received into the socket of the scapula (fig.\nLXV. 9. 7) termed, as has been stated (141), its glenoid cavity. The\nmiddle portion of the bone, or what is termed its shaft (fig. LXV. 8),\ndiminishes considerably in magnitude, and becomes somewhat rounded\n(fig. LXV. 8), while its lower end again enlarges, and is spread out\ninto a flattened surface of great extent (fig. LXIX. 1, 3, 2, 4). Of\nthis broad flattened surface, the middle portion is grooved (fig. LXIX.\n2): it is covered with cartilage; it forms the articulating surface\nby which the arm is connected with the fore-arm. On each side of this\ngroove there is a projection of bone or tubercle, termed condyle (fig.\nLXIX. 3, 4), the inner (fig. LXIX. 3) being much larger than the outer\n(fig. LXIX. 4). The inner condyle gives origin to the muscles that\nbend, the outer to those that extend the fore-arm and the fingers\n(figs. LXXXIV. 1, 2, and LXXXV. 1).\n\n[Illustration: Fig. LXIX.\n\n1. Lower extremity of the humerus; 2. grooved surface; 3. internal\ncondyle; 4. external condyle; 5. the upper part of the ulna; 6. the\nhead; 7. the neck; 8. the tubercle of the radius.]\n\n150. The muscles that act upon the arm arise from the back (fig.\nLXXII. 2), the chest (fig. LXXI. 1), the clavicle (fig. LXXI. 1), and\nthe scapula (fig. LXXI. 3); and they move the arm with freedom and\npower upwards, downwards, forwards, backwards, inwards, and outwards.\nThe chief muscle that raises the arm is the deltoid (fig. LXXI. 3),\nwhich arises partly from the clavicle and partly from the scapula\n(fig. LXXI. 3). It has the appearance of three muscles proceeding in\ndifferent directions, the different portions being separated by slight\nfissures (figs. LXXI. 3, and LXXII. 3). The fibres converging unite\nand form a powerful muscle which covers the joint of the humerus (fig.\nLXXI. 3). It is implanted by a short and strong tendon into the middle\nof the humerus (fig. LXXI. 4). Its manifest action is to pull the arm\ndirectly upwards. Its action is assisted by the muscles that cover\nthe back of the scapula, which are in like manner inserted into the\nhumerus, and which, at the same time that they elevate the arm, support\nit when raised.\n\n[Illustration: Fig. LXXI.\n\nView of the muscles on the fore part of the chest that act upon the\narm. 1. The muscle called the great pectoral; 2. the small pectoral; 3.\nthe deltoid; 4. the humerus.]\n\n151. The principal muscle that carries the arm downwards is the\nlatissimus dorsi (fig. LXXII. 2), the broadest muscle of the body,\nwhich, after having covered all the lower part of the back and loins,\nterminates in a thin but strong tendon which stretches to the arm, and\nis implanted into the humerus (fig. LXXII. 2), near the tendon of a\nmuscle immediately to be described,\u2014the great pectoral. When the arm\nis raised by the deltoid and its assistant muscles, the latissimus\ndorsi carries it downwards with force, and its powerful action is\nincreased by that of other muscles which arise from the scapula and are\ninserted into the arm.\n\n152. The principal muscle that carries the arm forwards towards the\nchest, is the great pectoral (fig. LXXI. 1), which, arising partly from\nthe clavicle (fig. LXXI. 1), partly from the sternum (fig. LXXI. 1),\nand partly from the cartilages of the second, third, fourth, fifth, and\nsixth ribs (fig. LXXI. 1), covers the greater part of the breast (fig.\nLXXI. 1). Its fibres, converging, terminate in a strong tendon, which\nis inserted near the tendon of the longissimus dorsi into the humerus,\nabout four inches below its head (fig. LXXI. 1). These two muscles form\nthe axilla or armpit, the anterior border of the axilla consisting of\nthe pectoral muscle. Though each of these muscles has its own peculiar\noffice, yet they often act in concert, thereby greatly increasing their\npower, and the result of their combined action is to carry the arm\neither directly downwards or to the side of the chest.\n\n[Illustration: Fig. LXXII.\n\nView of the muscles seated on the back part of the trunk that act\nupon the shoulder and arm. 1. The muscle called the trapezius; 2. the\nlatissimus dorsi; 3. the deltoid.]\n\n153. Some of the muscles that elevate the arm carry it inwards, and\nothers outwards; the muscles that carry it forwards likewise carry it\ninwards; while of the muscles that pull it downwards, some direct it\nforwards and inwards, and others backwards and outwards (151 and 152).\n\n154. It has been already stated that the shoulder-joint is completely\nsurrounded by the muscular fibres or the tendinous expansions of\nseveral of these powerful muscles, which have a far greater effect in\nmaintaining the head of the humerus in its socket than the fibrous\ncapsule of the joint; the latter being necessarily loose, in order\nto allow of the extended and varied motions of the arm, whereas the\nmuscles that encompass the joint adhere closely and firmly to it.\nMoreover, by virtue of their vital power these muscles act with an\nefficiency which a mere ligamentous band is incapable of exerting; for\nthey apportion the strength of resistance to the separating force, and\nreact with an energy proportioned to the violence applied.\n\n155. The bones of the fore-arm are two, the ulna and the radius (figs.\nLXIX. and LXXIII.). The ulna is essentially the bone of the elbow\n(figs. LXIX. 5, and LXXIII. 3); the radius that of the hand (fig.\nLXXV.). Supposing the arm to hang by the side of the body, and the palm\nof the hand to be turned forwards, the ulna, in apposition with the\nlittle finger, occupies the inner; and the radius, in apposition with\nthe thumb, occupies the outer part of the fore-arm (fig. XXXIV. 3).\n\n[Illustration: Fig. LXXIII.\n\n  1. The internal condyle of the humerus; 2. the external\n  condyle of the humerus; 3. the olecranon process of the ulna;\n  4. the head of the radius.]\n\n156. The upper end of the ulna belonging to the elbow is large (figs.\nLXIX. 5, and LXXIII. 3). It sends backwards the large projection\ncommonly named the elbow or _olecranon_ (fig. LXXII. 3), in the centre\nof which there is a smooth and somewhat triangular surface (fig.\nLXXIII. 3) which is always covered by skin of a coarse texture, like\nthat placed over the lower part of the knee-pan, as if nature intended\nthis for a part on which we may occasionally lean and rest. Large at\nthe elbow, the ulna gradually grows smaller and smaller as it descends\ntowards the wrist, where it ends in a small round head (fig. LXXXII.\n2), beyond which, on the inner side, or that corresponding to the\nlittle finger, it projects downwards a small rounded point, termed\nthe styloid process (fig. LXXXII. 3). As the styloid process and the\nolecranon, the two extremities of the ulna (figs. LXXIII. 3, and\nLXXII. 3), are easily and distinctly felt, the length of this bone was\nprimitively used as a measure, called a cubit, which was the ancient\nname of the bone.\n\n157. The radius, the second bone of the fore-arm, placed along its\nouter part next the thumb, is small at its upper end (figs. LXIX. 6,\nand LXXIII. 4); but its body is larger than that of the ulna; while its\nlower end, next the wrist to which it properly belongs, is very bulky\n(fig. LXXXII. 1). Its upper end is formed into a small circular head,\nwhich is united by distinct joints both to the humerus and to the ulna\n(fig. LXIX. 6). The top of its rounded head is excavated into a shallow\ncup (figs. LXIX. 6, and LXXIII. 4) which receives a corresponding\nconvexity of the humerus (fig. LXIX. 2), and its lower extremity is\nexcavated into an oblong cavity, which receives two of the bones of the\nwrist (fig. LXXXIII. 1. 4).\n\n158. The joint of the elbow is composed above of the condyles of the\nhumerus (fig. LXIX. 3. 2), and below by the heads of the ulna and\nradius (fig. LXIX. 5. 6).\n\n159. The upper surface of the ulna is so accurately adapted to the\nlower surface of the humerus that the one seems to be moulded on\nthe other (figs. LXIX. 5, and LXXIII. 3), and the form of these\ncorresponding surfaces, which are everywhere covered with cartilage,\nis such as to admit of free motion backwards and forwards, that is,\nof extension and flexion; but to prevent any degree of motion in any\nother direction. The joint is therefore a hinge-joint, of which the two\nmotions of flexion and extension are the proper motions. This hinge is\nformed on the part of the humerus by a grooved surface, with lateral\nprojections (fig. LXIX. 2, 3, 4), and on the part of the ulna by a\nmiddle projection with lateral depressions (fig. LXIX. 5): the middle\nprojection of the ulna turning readily on the grooved surface of the\nhumerus (fig. LXIX. 2).\n\n160. The bones are held in their proper situation, first, by a\nligament on the fore part of the arm, called the anterior (fig. LXXIV.\n6), which arises from the lower extremity of the humerus, and is\ninserted into the upper part of the ulna and the coronary ligament of\nthe radius (fig. LXXIV. 6. 8); secondly, by another ligament on the\nback part of the arm, called the posterior ligament (fig. LXXV. 8),\nplaced in the cavity of the humerus that receives the olecranon of the\nulna (fig. LXXV. 8); and thirdly, by two other ligaments at the sides\nof the ulna (fig. LXXV. 6, 7). The ulna and radius are united, first,\nby a ligament called the coronary, which, arising from the ulna, passes\ncompletely around the head of the radius (fig. LXXVI. 3), and the\nattachment of which, while sufficiently close to prevent the separation\nof the two bones, is yet not adherent to the radius, for a reason\nimmediately to be assigned; secondly, by another ligament which passes\nin an oblique direction from one bone to the other (fig. LXXVI. 4);\nand thirdly, by a dense and broad ligament, termed the _interosseous_\n(figs. LXXIV. 10, and LXXVI. 5), which fills up the space between the\ntwo bones nearly in their whole extent. This ligament serves other\noffices besides that of forming a bond of union, affording, more\nespecially, a greater extent of surface for the attachment of muscles,\nand separating the muscles on the anterior from those on the posterior\npart of the limb.\n\n[Illustration: Fig. LXXIV.\n\n  Anterior view of the ligaments of the elbow-joint. 1. The\n  lower portion of the humerus; 2. the upper portion of the\n  radius; 3. the upper portion of the ulna; 4. the internal\n  condyle; 5. the external condyle; 6. the anterior ligament;\n  7. portion of the internal lateral ligament; 8. portion of\n  the coronary ligament; 9. the oblique ligament; 10. upper\n  portion of the interosseous ligament.]\n\n[Illustration: Fig. LXXV.\n\n  Posterior view of the ligaments of the elbow-joint. 1. Lower\n  end of the humerus; 2. internal condyle; 3. external condyle;\n  4. the olecranon process of the ulna; 5. the upper portion of\n  the radius; 6. the internal lateral ligament; 7. the external\n  lateral ligament; 8. the posterior ligament.]\n\n[Illustration: Fig. LXXVI.\n\nView of the ligaments connecting the ulna and radius at their upper\npart. 1. The radius; 2. the ulna; 3. the coronary ligament surrounding\nthe head of the radius; 4. the oblique ligament passing from the ulna\nto the tubercle of the radius; 5 the upper portion of the interosseous\nligament.]\n\n161. At their inferior extremities the ulna and radius are united\npartly by the interosseous ligament (fig. LXXVII. 1) and partly by\nligamentous fibres which pass transversely from one bone to the other\n(fig. LXXVII. 2) on the anterior and the posterior surface of the\nfore-arm.\n\n[Illustration: Fig. LXXVII.\n\n1. Interosseous ligament; 2. transverse fibres passing between the\nradius and ulna, and uniting the two bones; 3. 4. 5. posterior and\nlateral ligaments of the wrist joint; 6. ligaments uniting the bones of\nthe wrist with one another; 7. 8. ligaments which attach the metacarpal\nto the carpal bones; 9. transverse ligaments for the attachment of the\nphalanges of the fingers; 10. lateral ligaments for the attachment of\nthe phalanges of the fingers 11. ligaments of the thumb.]\n\n162. The lower extremity of the radius is also united to the wrist;\nand the hand being attached to the wrist, the junction of the hand and\nthe fore-arm is effected by the articulation of the wrist with the\nradius (fig. LXXVII.). The ligaments which connect the bones of the\nwrist with the radius are bands of exceeding strength (fig. LXXVII. 3).\n\n163. The muscles that act upon the fore-arm are placed upon the arm\n(fig. LXXVIII.). The joint of the elbow being a hinge-joint, the\nfore-arm can admit only of two motions, namely, flexion and extension.\nThe muscles by which these motions are effected are four, two for each;\nthe two flexors being placed on the fore part (fig. LXXVIII. 2. 4), and\nthe two extensors on the back part of the arm (fig. LXXIX. 5).\n\n164. The two flexor muscles of the fore-arm are termed the biceps and\nthe brachialis (fig. LXXVIII. 2, 4). The biceps is so called because\nit has two distinct heads or points of origin (fig. LXXVIII. 2), both\nof which arise from the scapula (fig. LXXVIII. 2). About a third part\ndown the humerus the two heads meet, unite and form a bulky muscle\n(fig. LXXVIII. 2), which, when it contracts, may be felt like a firm\nball on the fore part of the arm, the upper part of the ball marking\nthe point of union of the two heads (fig. LXXVIII. 2). The muscle\ngradually becoming smaller, at length terminates in a rounded tendon\n(fig. LXXVIII. 3), which is implanted into the tubercle of the radius\na little below its neck (fig. LXXVIII. 3). It is an exceedingly thick\nand powerful muscle, and its manifest action is to bend the fore-arm\nwith great strength. But since its tendon is inserted into the radius,\nbesides bending the fore-arm, it assists other muscles that also act\nupon the radius in the performance of a function to be described\nimmediately (168).\n\n[Illustration: Fig. LXXVIII.\n\nView of the flexor muscles of the fore-arm. 1. The anterior surface\nof the scapula; 2. the muscle called biceps; 3. tendon of the biceps\npassing to the tubercle of the radius; 4. the muscle called brachialis.]\n\n165. The second flexor of the fore-arm, termed the brachialis, is\nplaced immediately under the biceps, and is concealed by it for a\nconsiderable part of its course (fig. LXXVIII. 4). Arising from the\nhumerus, on each side of the insertion of the deltoid, it continues its\nattachment to the bone all the way down the fore part of the humerus,\nto within inch of the joint; it then passes over the joint, adhering\nfirmly to the anterior ligament (fig. LXXVIII. 4), and is inserted by a\nstrong tendon into the ulna (fig. LXXVIII. 4). It is a thick and fleshy\nmuscle, powerfully assisting the action of the biceps.\n\n166. The two extensor muscles are named the triceps and the anconeous\n(fig. LXXIX.). The triceps, seated on the back part of the arm, derives\nits name from having three distinct points of origin, or three separate\nheads (fig. LXXIX. 5); one of which arises from the scapula and two\nfrom the humerus (fig. LXXIX. 5). All these heads adhere firmly to the\nhumerus, as the brachialis does on the fore part of the arm, down to\nwithin an inch of the joint (fig. LXXIX. 5), where they form a strong\ntendon, which is implanted into the olecranon of the ulna (fig. LXXIX.\n3); the projection of which affords a lever for increasing the action\nof the muscle. In all animals that leap and bound, this process of the\nulna is increased in length in proportion to their power of performing\nthese movements. The triceps forms an exceedingly thick and strong\nmuscle, which envelops the whole of the back part of the arm (fig.\nLXXIX.); its action is simple and obvious; it powerfully extends the\nfore-arm. The anconeous, a small muscle of a triangular form, arising\nfrom the external condyle of the humerus, and inserted into the ulna a\nlittle below the olecranon, assists the action of the triceps.\n\n[Illustration: Fig. LXXIX.\n\nView of the extensor muscles of the fore-arm. 1. The scapula; 2. the\nupper part of the humerus; 3. upper end of the ulna; 4. upper end\nof the radius; 5. the muscle called _triceps_, the extensor of the\nfore-arm.]\n\n167. Such are the motive powers which act upon the fore-arm, and\nwhich produce all the motions of which the hinge-joint of the elbow\nrenders it capable. But besides flexion and extension, the fore-arm is\ncapable of the motion of rotation, which is accomplished by means of\nthe radius. It has been shown (157) that the top of the rounded head of\nthe radius is excavated into a shallow cup (figs. LXIX. 6, and LXXIII.\n4) which receives a corresponding convexity of the humerus (figs.\nLXIX. 2, and LXXIII. 2). In consequence of this articulation with the\nhumerus, the radius, like the ulna, can move backwards and forwards\nin flexion and extension, the proper movements of the hinge-joint;\nbut that portion of the margin of the hinge of the radius which is in\napposition with the ulna is convex (fig. LXIX. 6), and is received into\na semilunar cavity hollowed out in the ulna (fig. LXIX. 5). In this\ncavity the rounded head of the radius revolves, the two bones being\nheld together by the ligament already described (160), which surrounds\nthe head of the radius (fig. LXXVI. 3), and which holds it firmly\nwithout being adherent to it, and without impeding in any degree the\nrotatory motion of the radius. Below, the surface of the radius next\nthe ulna is hollowed out into a semilunar cavity (fig. LXXXII. 1),\nwhich receives a corresponding convex surface of the ulna (fig. LXXXII.\n2), upon which convex surface the radius rolls (fig. LXXXII. 1). Thus,\nby the mode in which it is articulated with the ulna above, the radius\nturns upon its own axis. By the mode in which it is articulated with\nthe ulna below, the radius revolves upon the head of the ulna; and, in\nconsequence of both articulations, is capable of performing the motion\nof rotation. Moreover, the hand being attached to the radius through\nthe medium of the wrist (figs. LXXXII. 1. 4. and LXXXIII. 1. 4) must\nnecessarily follow every movement of the radius; the rotation of which\nbrings the hand into two opposite positions. In the one, the palm of\nthe hand is directed upwards (fig. LXXXII.); in the other, it is turned\ndownwards (fig. LXXXIII.). When the hand is turned upwards, it is said\nto be in the state of _supination_ (fig. LXXXII.); when downwards, in\nthat of _pronation_ (fig. LXXXIII.). A distinct apparatus of muscles\nis provided for effecting the rotation of the radius, in order to\nbring the hand into these opposite states: one set for producing its\nsupination, and another its pronation.\n\n168. The principal supinators arise from the external condyle of the\nhumerus (fig. LXXX.), and are called long and short (fig. LXXX. 4, 5).\nThe long supinator extends as far as the lower end of the radius, into\nwhich it is inserted (fig. LXXX. 4): the short supinator surrounds the\nupper part of the radius, and is attached to it in this situation (fig.\nLXXX. 5.). Moreover, the triceps, being inserted into the radius (164),\noften cooperates with the supinators and powerfully assists their\naction.\n\n169. The principal pronators are also two, called the round and the\nsquare (figs. LXXXI. and LXXXVI. 1). The round pronator arises from the\ninternal condyle, and passing downwards, is inserted into the middle\nof the radius (fig. LXXXI. 4); the square pronator is a small muscle\nbetween the radius and ulna, at their lower extremities being attached\nto each (fig. LXXXVI. 1).\n\n[Illustration: Fig. LXXX.\n\nView of the supinators of the radius and hand. 1. The humerus; 2. the\nulna; 3. the radius; 4. the muscle called the long supinator passing to\nbe inserted into the lower portion of the radius; 5. the muscle, called\nthe short supinator, surrounding the upper part of the radius.]\n\n170. The action of these muscles in producing the rotation of the\nradius, and so rendering the hand supine or prone, is sufficiently\nmanifest from the mere inspection of the diagrams (fig. LXXXI. 4).\n\n[Illustration: Fig. LXXXI.\n\nView of the pronators of the hand. 1. Lower end of the humerus; 2. the\nradius; 3. the ulna; 4. the muscle called the round _pronator_, one of\nthe powerful pronators of the hand.]\n\n171. The hand is composed of the carpus, metacarpus, and fingers.\n\n172. The carpus (fig. LXXXII. 4) consists of eight small wedge-shaped\nbones, placed in a double row, each row containing an equal number, and\nthe whole disposed like stones in an arch (fig. LXXXII. 4). They do in\nfact form an arch, the convexity of which is upwards, on the dorsal\nsurface (fig. LXXXIII. 4); and the concavity downwards, on the palmar\nsurface (fig. LXXXII. 4). But they differ from the stones of an arch\nin this, that each bone is joined to its fellow by a distinct moveable\njoint, each being covered with a smooth articulating cartilage. At the\nsame time all of them are tied together by ligaments of prodigious\nstrength, which cross each other in every direction (fig. LXXVII. 6),\nso that the several separate joints are consolidated into one great\njoint. The consequence of this mechanism is that some degree of motion\nis capable of taking place between the several bones, which, when\nmultiplied together, gives to the two rows of bones such an extent of\nmotion, that when the wrist is bent the arch of the carpus forms a kind\nof knuckle. By this construction a facility and ease of motion, and\na power of accommodation to motion and force, are obtained, such as\nbelong to no arch contrived by human ingenuity.\n\n[Illustration: Fig. LXXXII.\n\n1. Lower extremity of the radius; 2. lower extremity of the ulna;\n3. styloid process of the ulna; 4. bones of the carpus or wrist;\n5. metacarpal bones; 6. first phalanges of the fingers; 7. second\nphalanges of the fingers; 8. third phalanges of the fingers.]\n\n173. The metacarpus (fig. LXXXII. 5), the middle portion of the hand,\ninterposed between the wrist and the fingers, is composed of five\nbones, which are placed parallel to each other (fig. LXXXII. 5). They\nare convex outwardly, forming the back (fig. LXXXIII. 5), and concave\ninwardly, forming the hollow of the hand (fig. LXXXII. 5). They are\nlarge at each end, to form the joints by which they are connected with\nthe wrist and fingers (figs. LXXXII. and LXXXIII.): they are small in\nthe middle, in order to afford room for the lodgment and arrangement\nof the muscles, that move the fingers from side to side (fig. LXXXVI.\n2). Their ends, which are joined to the carpus, are connected by nearly\nplane surfaces (figs. LXXXII. and LXXXIII.): their ends, which support\nthe fingers, are formed into rounded heads, which are received into\ncorresponding cup-shaped cavities, excavated in the top of the first\nbones of the fingers (fig. LXXXII. 5.). The powerful ligaments that\nunite these bones pass, both on the dorsal and the palmar surface, from\nthe inferior extremity of the second row of the carpal to the bases of\nthe metacarpal bones (fig. LXXVII, 7, 8). The ligaments are arranged in\nsuch a manner as to limit the motions of the joints chiefly to those\nof flexion and extension, allowing, however, a slight degree of motion\nfrom side to side.\n\n174. Each of the fingers is composed of three separate pieces of bone,\ncalled phalanges; the thumb has only two (fig. LXXXII. 6, 7, 8): the\nphalanges are convex outwardly (fig. LXXXII. 6, 7, 8) for increasing\ntheir strength, and flattened inwardly (fig. LXXXIII. 6, 7, 8) for\nthe convenience of grasping. The last bones of the fingers, which are\nsmall, terminate at their under ends, in a somewhat rounded and rough\nsurface (fig. LXXXIII. 8), on which rests the vascular, pulpy, and\nnervous substance, constituting the special organ of touch, placed at\nthe points of the fingers, and guarded on the upper surface by the nail\n(fig. LXXXII. 8).\n\n[Illustration: Fig. LXXXIII.\n\n1. Lower extremity of the radius; 2. lower extremity of the ulna; 3.\nstyloid process of the ulna; 4. bones of the carpus; 5. metacarpal\nbones; 6. 7. 8. first, second, and third phalanges of the fingers.]\n\n175. The round inferior extremity of the metacarpus is admitted into\nthe cavity of the superior extremity of the first phalanx of the five\nfingers (figs. LXXXII. and LXXXIII.), and their joints are connected by\nlateral and transverse ligaments of great strength (fig. LXXVII. 9).\nThe situation and direction of the ligaments which unite the several\nphalanges of the fingers (fig. LXXVII. 9) are precisely the same as\nthose of the articulation of the phalanges with the metacarpus (fig.\nLXXVII. 7, 8); and the articulation of these bones with one another is\nsuch as to admit only of the motions of flexion and extension.\n\n176. The muscles which perform these motions are seated for the most\npart on the fore-arm. Independently of the supinators and pronators\nwhich have been already described (167 et seq.), there are distinct\nsets of muscles for bending and extending the wrist and the fingers.\nThe flexors arise from the internal, and the extensors from the\nexternal, condyle of the humerus (fig. LXIX. 3, 4). The internal\ncondyle is larger and longer than the external (fig. LXIX. 3, 4); for\nthe flexors require a larger point of origin and a longer fulcrum\nthan the extensor muscles; because to the actions of flexion, such as\ngrasping, bending, pulling, more power is necessary than to the action\nof extension, which consists merely in the unfolding or the opening of\nthe hand previously to the renewal of the grasp.\n\n177. For the same reason, two muscles are provided for flexing,\nwhile only one is provided for extending the fingers. The flexors,\nbulky, thick, and strong, are placed on the fore part of the fore-arm\n(fig. LXXXIV.). The first, named the superficial flexor (fig. LXXXIV.\n1), about the middle of the arm, divides into four fleshy portions,\neach of which ends in a slender tendon (fig. LXXXIV. 1). As these\ntendons approach the fingers they expand (fig. LXXXIV. 1), and when\nin apposition with the first phalanx, split and form distinct sheaths\nfor the reception of the tendons of the second flexor (fig. LXXXIV.\n3). After completing the sheath, the tendons proceed forward along the\nsecond phalanx, into the fore part of which they are implanted, and\nthe chief office of this powerful muscle is to bend the second joint\nof the fingers upon the first, and the first upon the metacarpal bone.\nIts action is assisted by a second muscle, called the deep or profound\nflexor (fig. LXXXIV. 2), because it lies beneath the former; or the\nperforans, because it pierces it. Bulky and fleshy, this second flexor,\nlike the first, about the middle of the arm, divides into four tendons,\nwhich, entering the sheaths prepared for them in the former muscle\n(where the tendons are small and rounded for their easy transmission\nand play), pass to the root of the third phalanx of the fingers into\nwhich they are implanted (fig. LXXXIV. 3).\n\n[Illustration: Fig. LXXXIV.\n\nView of the flexor muscles of the fingers. 1. The superficial flexor,\ndivided and turned aside, to show, 2. the deep flexor; 3. sheaths for\nthe tendons of the deep flexor, formed by the splitting of the tendons\nof the superficial flexor; 4. the anterior annular ligament, divided\nand turned aside.]\n\n118. The muscle that extends the fingers, called the common extensor,\nis placed on the back part of the fore-arm (fig. LXXXV.), about the\nmiddle of which it divides into four portions which terminate in\nso many tendons (fig. LXXXV. 2). When they reach the back of the\nmetacarpal bones, these tendons become broad and flat, and send\ntendinous expansions to each other, forming a strong tendinous sheath\nwhich surrounds the back of the fingers (fig. LXXXV. 2). These\ntendinous expansions are inserted into the posterior part of the bones\nof the four fingers (fig. LXXXV. 2); and their office is powerfully to\nextend all the joints of all the fingers (fig. LXXXV. 2).\n\n179. On both the palmar and dorsal regions of the wrist are placed\nligaments for tying down these tendons, and preventing them from\nstarting from their situation during the action of the muscles (figs.\nLXXXIV. and LXXXV.). On the palmar region an exceedingly strong\nligament passes anteriorly to the concave arch of the carpus (fig.\nLXXXIV. 4) for the purpose of tying down the tendons of the flexor\nmuscles. On the dorsal surface (fig. LXXXV.), a similar ligament,\npassing in an oblique direction from the styloid process of the radius\nto the styloid process of the ulna (fig. LXXXV. 3), performs the same\noffice in tying down the tendons of the extensor muscle. Both these\nligaments are called annular.\n\n[Illustration: Fig. LXXXV.\n\nView of the extensor muscles of the fingers. 1. The common extensor,\nsending (2 2 2 2) tendons to each finger; 3. the posterior annular\nligament.]\n\n180. In the palm of the hand are placed additional muscles which\nassist the flexors of the fingers (fig. LXXXVI. 2), being chiefly\nuseful in enabling the fingers to perform with strength and precision\nshort and quick motions. There are especially four small and rounded\nmuscles (fig. LXXXVI. 2), resembling the earth worm in form and size,\nand hence called lumbricales; but as their chief use is to assist the\nfingers in executing short and rapid motions, they have also received\nthe better name of the musculi fidicinales.\n\n[Illustration: Fig. LXXXVI.\n\n1. The muscle called the square pronator; 2. muscles seated in the palm\nof the hand, by which, chiefly, the fingers execute short and rapid\nmotions.]\n\n181. The thumb, in consequence of the comparative looseness of its\nligaments, is capable of a much greater extent of motion than the\nfingers, and can be applied to any part of each of the fingers, to\ndifferent parts of the hand, and in direct opposition to the power\nexerted by the whole of the fingers and hand, in the act of grasping.\nThe muscles which enable it to perform these varied motions, and which\nact powerfully in almost every thing we do with the hand, form a mass\nof flesh at the ball of the thumb (fig. LXXXVII. 1), almost entirely\nsurrounding it. The little finger is also provided with a distinct\napparatus of muscles (fig. LXXXVII. 2), which surrounds its root, just\nas those of the thumb surround its ball, in order to keep it firm in\nopposition to the power of the thumb in the act of grasping, and in\nvarious other motions.\n\n[Illustration: Fig. LXXXVII.\n\n1. The mass of muscles forming the ball of the thumb; 2. the mass of\nmuscles forming the ball of the little finger; 3. tendons of one of the\nflexor muscles of the fingers; 4. sheaths formed by the tendons of the\nsuperficial flexor for the reception of the tendons of the deep flexor.]\n\n182. The upper extremity is covered by a tendinous expansion or fascia\nwhich envelopes the whole arm, encloses its muscles as in a sheath,\nand affords them, in their strong actions, \"that kind of support which\nworkmen feel in binding their arms with thongs.\" This fascia likewise\ndescends between many of the muscles, forming strong partitions between\nthem, and affording points of origin to many of their fibres, scarcely\nless fixed than bone itself.\n\n183. From the whole, it appears, that the first joint of the upper\nextremities, that of the shoulder, is a ball and socket joint, a joint\nadmitting of motion in every direction; that the second joint, that of\nthe elbow, is partly a hinge-joint, admitting of flexion and extension,\nand partly a rotation joint, admitting of a turning or rotatory motion;\nand that the joints of the wrist and of the fingers are likewise\nhinge-joints, admitting at the same time of some degree of lateral\nmotion. When these various motions are combined, the result is that\nthe hand can apply itself to bodies in almost every direction, in any\npart of the area described by the arm, when all the joints are moved to\ntheir utmost extent. There is thus formed an instrument of considerable\nstrength, capable of a surprising variety and complexity of movements,\ncapable of seizing, holding, pulling, pushing and striking with great\npower, yet at the same time capable of apprehending the minutest\nobjects, and of guiding them with the utmost gentleness, precision, and\naccuracy, so that there are few conceptions of the designing mind which\ncannot be executed by the skilful hand.\n\n184. The lower extremities consist of the thigh, leg, and foot.\n\n185. The osseous part of the thigh consists of a single bone, called\nthe femur (fig. XXXIV. 4), the longest, thickest, and strongest bone in\nthe body. It sustains the entire weight of the trunk, and occasionally\nmuch heavier loads superimposed upon it. It is constructed in such\na manner as to combine strength with lightness. This is effected by\nrendering the bone what is technically called cylindrical; that is, a\nbone in which the osseous fibres are arranged around a hollow cylinder.\nThere are two varieties of osseous matter,\u2014the compact, in which the\nfibres are dense and solid (fig. LXXXVIII. 1), and the spongy, in which\nthe fibres are comparatively tender and delicate (fig. LXXXVIII. 2).\nBoth varieties are, indeed, combined, more or less, in every bone,\nthe compact substance being always external, and the spongy internal;\nbut in the cylindrical bones the arrangement is peculiar. Every long\nor cylindrical bone consists of a body or shaft (fig. LXXXVIII. 4.),\nand of two extremities (fig. LXXXVIII. 5). The body is composed\nprincipally of compact substance, which on the external surface is so\ndense and solid, that scarcely any distinct arrangement is visible;\nbut towards the interior this density diminishes; the fibres become\ndistinct (fig. LXXXVIII. 5), and form an expanded tissue of a cellular\nappearance (fig. LXXXVIII. 5), the cells being called cancelli, and\nthe structure cancellated. In the centre of the bone even the cancelli\ndisappear; the osseous fibres terminate; and a hollow space is left\nfilled up, in the natural state, by an infinite number of minute\nmembranous bags which contain the marrow (fig. LXXXVIII. 3). In the\nbody of the bone, to which strength is requisite, that part being the\nmost exposed to external violence, the compact matter is arranged\naround a central cavity. By this means strength is secured without\nany addition of weight; for the resisting power of a cylindrical body\nincreases in proportion to its diameter; consequently the same number\nof osseous fibres placed around the circumference of a circle produce\na stronger bone than could have been constructed had the fibres been\nconsolidated in the centre, and had the diameter been proportionally\ndiminished. The hollow space thus gained in its centre, renders the\nbone lighter by the subtraction of the weight of as many fibres as\nwould have gone to fill up that space; while its strength is not only\nnot diminished by this arrangement, but positively increased. On the\nother hand, at the extremities of the bone, space, not strength, is\nrequired; required for the attachment and arrangement of the tendons\nof the muscles that act upon it, and for the formation of joints (fig.\nLXXXVIII. 5). Accordingly, at its extremities the bone swells out into\nbulky surfaces; but these surfaces are composed, not of dense and solid\nsubstance, but of spongy tissue, covered by an exceedingly thin crust\nof compact matter, and so, as by the former expedient strength is\nsecured without increase of weight, by this, space is obtained without\nincrease of weight.\n\n[Illustration: Fig. LXXXVIII.\n\nA section of the femur, showing, 1. the compact bony substance; 2. the\nspongy or cancellated structure; 3. the internal cavity containing the\nmarrow; 4. body; 5, extremities of the bone.]\n\n186. The thigh-bone, placed at the under and outer part of the pelvis,\nhas an oblique direction, the under being considerably nearer its\nfellow than the upper end (fig. XXXIV. 4), in order to afford space for\nthe passages at the bottom of the pelvis, and also to favour the action\nof walking. The body of the bone, which is of a rounded form (fig.\nXXXIV. 4), is smooth on its anterior surface (fig. XXXIV. 4), where it\nis always slightly convex, the convexity being forwards (fig. XXXIV.\n4), while its posterior surface is irregular and rough, and forms a\nsharp prominent line, termed the linea aspera (fig. XXXV. 4), giving\nattachment to numerous muscles.\n\n187. The superior extremity of the femur terminates in a large ball or\nhead, which forms nearly two-thirds of a sphere (fig. LXXXIX. 4.). It\nis smooth, covered with cartilage, and received into the socket of the\nilium called the acetabulum, which, deep as it is, is still further\ndeepened by the cartilage which borders the brim (fig. LXXXIX. 3). The\nbrim is particularly high in the upper and outer part, because it is in\nthis direction that the reaction of the ground against the descending\nweight of the trunk tends to dislodge the ball from its socket.\n\n188. Passing obliquely downwards and outwards from the ball, is that\npart of the femur which is called the neck (fig. LXXXIX. 5). It spreads\nout archlike between the head and the body of the bone, and is more\nthan an inch in length (fig. LXXXIX. 5). It is thus long in order\nthat the head of the bone may be set deep in its socket, and that its\nmotions may be wide, free, and unembarrassed.\n\n[Illustration: Fig. LXXXIX.\n\n1. Lower portion of the ilium; 2. tuberosity of the ischium: 3. socket\nfor the head of the femur, or thigh-bone; 4. head of the femur; 5. neck\nof the femur; 6. the great process of the femur called the trochanter\nmajor; 7. the body of the femur.]\n\n189. From the external surface of the femur, nearly in a line with\nits axis, proceeds the largest and strongest bony process of the body\nwhich gives insertion to its most powerful muscles, namely, those that\nextend the thigh and that turn it upon its axis (fig. LXXXIX. 6).\nBecause, from its oblique direction, it rotates the thigh, this process\nis called the trochanter, and, from its size, the trochanter major. At\nthe under and inner part of the neck on the posterior surface of the\nbone, is a similar process, but much smaller, called the trochanter\nminor (fig. XXXV. 4), into which are inserted the muscles that bend the\nthigh.\n\n190. The inferior extremity of the femur, much broader and thicker\nthan the superior (fig. XC. 1), is terminated by two eminences, with\nsmooth surfaces, termed condyles (fig. XC. 2), which, articulated with\nthe tibia, and the patella, form the joint of the knee (figs. XC. 2, 4,\n5, and XCI. 1, 2, 3).\n\n[Illustration: Fig. XC.\n\n1. Lower end of the femur; 2. condyles of the femur; 3. upper end of\nthe tibia; 4. articular surfaces on the head of the tibia on which the\nthigh-bone plays; 5. the patella, or knee-pan; 6. upper end of the\nfibula, not entering into the knee-joint.]\n\n[Illustration: Fig. XCI.\n\nPosterior view of the bones forming the knee-joint. 1. Lower end of the\nfemur; 2. upper end of the tibia; 3. articular surfaces on the head of\nthe tibia, on which the thigh-bone plays; 4. upper end of the fibula,\nnot entering into the knee joint.]\n\n191. The bones of the leg, two in number, consist of the tibia (fig.\nXC. 3) and fibula (fig. XC. 6). The tibia, next to the femur, the\nlongest bone in the body, is situated at the inner side of the leg\n(fig. XC. 3). Its superior extremity is bulky and thick (fig. XC. 3).\nThe top of it forms two smooth and slightly concave surfaces, adapted\nto the convex surfaces of the condyles of the femur (fig. XC. 4, 2).\nOn its outer side there is a smooth surface, to which the head of the\nfibula is attached (fig. XC. 6). Its lower extremity, which is small,\nforms a concavity adapted to the convexity of the bone of the tarsus,\ncalled the astragalus, with which it is articulated (fig. XCII. 4.)\nIts inner part is produced so as to form the inner ankle (figs. XCII.\n2, and XCIII. 3): its outer side is excavated into a semilunar cavity,\nfor receiving the under end of the fibula, which forms the outer ankle\n(figs. XCII. 3, and XCIII. 4).\n\n192. The fibula, in proportion to its length the most slender bone of\nthe body, is situated at the outer side of the tibia (fig. XC. 6). Its\nupper end formed into a head, with a flat surface on its inner side\n(figs. XC. 6, and XCI. 4), is firmly united to the tibia (fig. XC. 4).\nIts lower end forms the outer ankle, which is lower and farther back\nthan the inner (fig. XCII. 3, 2).\n\n[Illustration: Fig. XCII.\n\nAnterior view of the bones forming the ankle-joint. 1. Lower end of\nthe tibia; 2. production of the tibia, forming the inner ankle; 3.\nlower end of the fibula, forming the outer ankle; 4. upper part of the\nastragalus: these three bones form the ankle-joint; 5 5 5, other bones\nof the tarsus; 6 6 6 6 6 metatarsal bones.]\n\n[Illustration: Fig. XCIII.\n\nPosterior view of the bones forming the ankle-joint. 1. Lower end of\nthe tibia; 2. lower end of the fibula; 3. internal malleolus or ankle;\n4. external malleolus or ankle; 5. one of the tarsal bones, called the\nastragalus, with which the tibia and fibula are articulated; 6. the os\ncalcis or heel.]\n\n193. The patella, or knee-pan (fig. XC. 5), is a light but strong\nbone, of the figure of the heart as painted on playing-cards, placed\nat the fore part of the joint of the knee, and attached by a strong\nligament to the tibia, the motions of which it follows (fig. XC. 5). It\nis lodged, when the knee is extended, in a cavity formed for it in the\nfemur (fig. XC.); when bent, in a cavity formed for it at the fore part\nof the knee (fig. XC. 5).\n\n194. The foot consists of the tarsus, metatarsus, and toes.\n\n195. The tarsus, or instep, is composed of seven strong,\nirregular-shaped bones, disposed like those of the carpus, in a double\nrow (fig. XCII. 4, 5). The arrangement of the tarsal bones is such as\nto form an arch, the convexity of which above, constitutes the upper\nsurface of the instep (fig. XCII. 4, 5): in the concavity below are\nlodged the muscles, vessels, and nerves that belong to the sole.\n\n196. The metatarsus consists of five bones, which are placed parallel\nto each other (fig. XCII. 6), and which extend between the tarsus\nand the proper bones of the toes (fig. XCII. 6). Their extremities,\nespecially next the tarsus, are large, in order that they may form\nsecure articulations with the tarsal bones (fig. XCII. 6). Their\nbodies are arched upwards (fig. XCII. 6), slightly concave below, and\nterminate forwards in small, neat, round heads, which receive the\nfirst bones of the toes, and with which they form joints, admitting\nof a much greater degree of rotation than is ever actually exercised,\nin consequence of the practice of wearing shoes. The natural, free,\nwide-spreading form of the toes, and the consequent security with\nwhich they grasp the ground, is greatly impaired by this custom. Taken\ntogether, the bones of the metatarsus form a second arch corresponding\nto that of the tarsus (fig. XCVIII. 2).\n\n197. Each toe consists of three distinct bones, called, like those\nof the fingers, phalanges (fig. XCVIII.), but the great toe, like\nthe thumb, has only two (fig. XCVIII.). That extremity of the first\nphalanges which is next the metatarsal bones is hollowed into a socket\nfor the head of the metatarsal bones.\n\n198. Besides the bones already described, there are other small bones,\nof the size and figure of flattened peas, found in certain parts of\nthe extremities, never in the trunk, called sesamoid, from their\nresemblance to the seed of the sesamum. They belong rather to the\ntendons of the muscles than to the bones of the skeleton. They are\nembedded within the substance of tendons, are found especially at the\nroots of the thumb and of the great toe, and are always placed in the\ndirection of flexion. Their office, like that of the patella, which is,\nin truth, a bone of this class, is to increase the power of the flexor\nmuscles by altering the line of their direction, that is, by removing\nthem farther from the axis of the bone on which they are intended to\nact.\n\n199. The ligaments which connect the bones of the lower extremities\nare the firmest and strongest in the body. Of these, the fibrous\ncapsule of the hip-joint (fig. XCIV. 1), which secures the head of the\nfemur in the cavity of the acetabulum (fig. XCIV.), is the thickest and\nstrongest. It completely surrounds the joint (fig. XCIV. 1). It arises\nfrom the whole circumference of the acetabulum, and, proceeding in a\ndirection outwards and backwards, is attached below to the neck of the\nfemur (fig. XCIV. 1). It is thicker, stronger, and much more closely\nattached to the bones than the fibrous capsule of the shoulder-joint\n(144), because the hip-joint is formed, not like the shoulder-joint,\nfor extent of motion, but for strength. Its internal surface is\nlined by synovial membrane, and its external surface is covered and\nstrengthened by the insertion of muscles that move the thigh-bone.\nThe joint is strengthened by another ligament, which passes from the\ninner and fore part of the cavity of the acetabulum (fig. XCV.) to be\ninserted into the head of the femur (fig. XCIV.), called the round\nligament, the office of which obviously is to hold the head of the\nfemur firmly in its socket.\n\n[Illustration: Fig. XCIV.\n\n1. The fibrous capsule of the hip-joint, laid open and turned aside to\nshow, 2. the round ligament in its natural position.]\n\n[Illustration: Fig. XCV.\n\nA view of the head of the femur drawn out of its socket, and suspended\nby the round ligament, to show more clearly the action of the ligament\nin retaining the head of the femur in its socket.]\n\n200. Numerous and complicated ligaments connect the bones that form\nthe knee-joint (fig. XCVI.), and the strength of these powerful bands\nis greatly increased by the tendons that move the leg (fig. XCVI. 5),\nwhich pass over, and more or less surround, the joint.\n\n[Illustration: Fig. XCVI.\n\nGeneral view of the ligaments of the knee-joint. 1. Lower end of the\nfemur; 2. upper end of the tibia; 3. upper end of the fibula; 4. the\npatella; 5. united tendons of the extensor muscles; 6. ligaments of\nthe patella; 7. the capsular investment of the knee; 8. the internal\nlateral ligament; 9. the external lateral ligaments; 10. the posterior\nligament; 11. the ligament connecting the tibia and fibula; 12. a\nportion of the interosseous ligament.]\n\n201. Strong ligaments maintain in their proper position the bones that\nform the ankle-joint (fig. XCVII.), connect the bones of the tarsus\nand metatarsus with one another (fig. XCVIII. 1), and articulate the\nseveral phalanges of the toes (fig. XCVIII. 2).\n\n[Illustration: Fig. XCVII.\n\nGeneral view of the posterior ligaments of the ankle-joint. 1. Lower\nend of the tibia; 2. lower end of the fibula; 3. astragalus; 4. os\ncalcis; 5. ligament between the tibia and fibula; 6. ligament passing\nfrom the fibula to the astragalus; 7. ligament passing from the fibula\nto the os calcis; 8. ligament passing from the tibia to the astragalus.]\n\n[Illustration: Fig. XCVIII.\n\nGeneral view of the ligaments of the sole of the foot. 1. Ligaments\nconnecting the bones of the tarsus; 2. ligaments connecting the bones\nof the toes.]\n\n202. The joint of the hip, like that of the shoulder, is capable of\nflexion, extension, and rotation; but its rotatory motions are to a\nmuch less extent, on account of the greater depth of the acetabulum and\nthe stronger and shorter fibrous capsule. When the femur is flexed, the\nthigh is bent upon the pelvis, and its inferior extremity is carried\nforwards. When it is extended, the thigh is carried backwards. The\ntwo thighs may be separated from each other laterally (abduction), or\nbrought near to each other (adduction), or the one may be made to cross\nthe other, and they may be rotated outwards or inwards.\n\n203. The apparatus of muscles that produces these varied motions is\nseated partly on the trunk and partly on the pelvis. Thus, the powerful\nmuscle that flexes the thigh, or that carries it forwards, termed\nthe psoas (fig. XCIX. 1), arises from the last vertebra of the back,\nand successively from each vertebra of the loins (fig. XCIX. 1), and\nis inserted into the lesser trochanter of the femur (fig. XCIX. 3).\nIts action is assisted first by a large and strong muscle named the\niliacus (fig. XCIX. 2), which occupies the whole concavity of the ilium\n(fig. XCIX. 2), and which, like the psoas, is inserted into the lesser\ntrochanter of the femur (fig. XCIX. 3).\n\n[Illustration: Fig. XCIX.\n\nView of the muscles that bend the thigh. 1. The muscle called psoas;\n2. the muscle called iliacus; 3. tendons of these muscles, going to be\ninserted into the trochanter minor of the femur.]\n\n204. The muscles that extend the thigh, or that carry it backwards,\nnamed the glut\u00e6i, the most powerful muscles of the body, are placed\nin successive layers, one upon the other, on the back part of the\nilium (fig. C. 1, 2, 3), and are inserted into the linea aspera of the\nfemur. They constitute the mass of flesh which forms the hip, and their\npowerful action in drawing the thigh backwards is assisted by several\nother muscles (fig. C. 4, 5, 6). Their action is never perfectly simple\nand direct; for those which move the thigh forwards sometimes carry it\ninwards, and sometimes outwards; and in like manner, those which move\nit backwards, at one time carry it inwards and at another outwards,\naccording to the direction of the fibres of the muscle and the position\nof the limb when those fibres act; while some of them, and more\nespecially those which carry it backwards, at the same time rotate it,\nor roll it upon its axis.\n\n[Illustration: Fig. C.\n\nView of the muscles that extend the thigh. 1. The muscle called glut\u00e6us\nmaximus, removed from its origin, 2, 2, to show the muscles which lie\nbeneath it; 2. cut edge showing the origin of the same muscle; 3. the\nmuscle called glut\u00e6us medius; 4, 5, 6. smaller muscles, assisting the\naction of the glut\u00e6i.]\n\n205. The knee is a hinge-joint, admitting only of flexion and\nextension, and is therefore provided only with two sets of muscles, one\nfor bending and the other for extending the leg. The flexors of the leg\narise from the under and back part of the pelvis, are seated on the\nback part of the thigh, and are inserted into the upper part either of\nthe tibia or of the fibula (fig. CI). They consist for the most part of\nthree muscles, named the semi-tendinosus, the semi-membranosus (fig.\nCI. 3), and the biceps of the leg (fig. CI. 1). The tendons of the two\nformer muscles, in passing to be inserted into the leg, form the inner,\nand that of the latter the outer, hamstrings (fig. CI. 4, 5).\n\n[Illustration: Fig. CII.\n\nView of the flexor and extensor muscles of the leg. 1. The biceps of\nthe leg; 2. tendon of the biceps, inserted into the head of the fibula;\n3. the semi-membranosus, passing to be inserted into the head of the\nfibula; 4. tendon of the semi-membranosus forming the inner, and 5.\ntendon of the biceps forming the outer, hamstring; 6. upper part of the\ngastrocnemius muscle; 7. the four large muscles which unite to form the\ngreat extensor muscle of the leg, inserted into 8. the patella; 9. a\nportion of the glut\u00e6us maximus concealing the other muscles of the hip.]\n\n206. Four large muscles, blended together in such a manner as to form\none muscle of prodigious size, termed the quadriceps cruris (fig. CI.\n7), occupying nearly all the forepart and the sides, and a considerable\nportion of the back part of the thigh, constitute the great flexor of\nthe thigh. This enormous mass of muscle arises partly from the ischium,\nand partly from the upper part of the femur (fig. CI. 7), and is all\ninserted into the patella (fig. CI. 8), which constitutes a pulley for\nthe purpose of assisting the action of these powerful muscles.\n\n207. The muscles which bend the toes and extend the foot, termed the\ngastrocnemii (fig. CII. 1, 2), are placed on the back part of the leg,\nand form the mass of muscle which constitutes the calf of the leg (fig.\nCII. 1, 2). They arise partly from the lower extremity of the femur\n(fig. CII.) and partly from the upper and back part of the fibula and\ntibia; and they form the largest and strongest tendon in the body,\ntermed the tendo achillis (fig. CII. 3), which is implanted into the\nheel (fig. CII. 4).\n\n[Illustration: Fig. CII.\n\nView of the muscles which bend the toes, and which, by lifting the\nheel, extend the foot. 1. The muscle called gastrocnemius externus,\nwhich, uniting with 2. the gastrocnemius internus, forms 3. the tendo\nachillis, which is inserted into 4. the heel.]\n\n[Illustration: Fig. CIII.\n\nView of the muscles which extend the toes and bend the foot. 1. The\ncommon extensor; 2. the tendons of the same muscle inserted into the\ntoes; 3. the anterior annular ligament of the foot.]\n\n[Illustration: Fig. CIV.\n\nView of the muscles in the sole of the foot. 1 The muscle which draws\nthe great toe from the other toes; 2. the muscle which draws the little\ntoe from the other toes; 3. the muscle called the short flexor of the\ntoes, which assists in bending the four smaller toes.]\n\n208. The muscles which extend the toes and bend the foot are seated\non the fore part of the leg (fig. CIII.); split into tendons like the\nanalogous muscles of the fingers (fig. CIII. 2); and are bound down\nby a ligament (fig. CIII. 3), exactly the same in name, disposition,\nand office, as that which belongs to the hand (fig. CIII. 3). Numerous\nminute muscles are placed in the sole of the foot (fig. CIV.), which\nact on the toes as the small muscles in the palm of the hand act on the\nfingers (fig. LXXXVI.).\n\n209. Such are the moving powers which put in action the complicated\nmechanism provided for the function of locomotion. And these powers are\nadequate to their office; but they are what may be termed expensive\npowers; agents requiring a high degree, of organization and the utmost\nresources of the economy to support and maintain them. Hence in the\nconstruction of the framework of the machine which they have to move,\nwhatever mechanical contrivance may economize their labour, is adopted.\nThe construction, form, and disposition of the several parts of that\nframework have all reference to two objects: first, the combination\nof strength with lightness; and secondly, security to tender organs,\nwith the power of executing rapid, energetic, and, sometimes, violent\nmotions. The combination is effected and the object attained in a mode\ncomplicated in the detail, simple in the design, and perfect in the\nresult. The weight of the body transmitted from the arch of the pelvis\nto a second arch, formed by the neck of the thigh-bone, and from this,\nin a perpendicular direction, to a third arch formed by the foot, is\nultimately received by the heel behind, and by the metatarsal bones\nand the first phalanges of the toes before, and more especially by the\nmetatarsal joints belonging to the great and little toe, which have a\nspecial apparatus of muscles, for the purpose of preserving steadily\ntheir relative situation to the heel. The weight of the body is thus\nsustained on a series of arches, from which it is, in succession,\ntransmitted to the ground, where it ultimately rests upon a tripod:\nforms known and selected as the best adapted to afford support, and to\ngive security of position. Columns of compact bone superimposed one\nupon another, and united at different points by bands of prodigious\nstrength, form the pillars of support. But these bony columns never\ntouch each other; are never in actual contact; are all separated by\nlayers of elastic matter which, while they assist in binding the\ncolumns together, enable them to move one upon another, as upon so many\npliant springs. The layers of cartilage interposed between the several\nvertebr\u00e6; the layer of cartilage interposed between the vertebral\ncolumn and the pelvis; the layer of cartilage that lines the acetabulum\nand that covers the head of the femur; the layer of cartilage that\ncovers the lower extremity of the femur and the upper extremity of the\ntibia and fibula and the tarsus; the successive layers of cartilage\ninterposed between the several bones of the tarsus; and finally,\nthe layer of cartilage that covers both the tarsal and the digital\nextremities of the metatarsal bones; are so many special provisions to\nprevent the weight of the body from being transmitted to the ground\nwith a shock; and, at the same time, so many barriers established\nbetween the ground and the spinal cord, the brain and the soft and\ntender organs contained in the thoracic and abdominal cavities, to\nprevent these organs from being injured by the reaction of the ground\nupon the body. The excellence of this mechanism is seen in its results;\nin contemplating \"from what heights we can leap\u2014to what heights we can\nspring\u2014to what distances we can bound\u2014how swiftly we can run\u2014how\nfirmly we can stand\u2014how nimbly we can dance\u2014and yet how perfectly we\ncan balance ourselves upon the smallest surfaces of support!\"\n\n210. It is necessary, in order to complete this general view of the\nstructure of the human body, and of the combination and arrangement\nof its various parts, to denote the several regions into which, for\nthe purpose of describing with accuracy the situation and relation of\nits more important organs, the body is divided. It is not needful to\nthe present purpose to describe the regions of the head, because its\ninternal cavity contains only one organ, the brain, and its external\ndivisions do not differ materially from those which are common\nand familiar; but the chest, the abdomen, and the upper and lower\nextremities are mapped out into regions, of which it is very important\nto have an exact knowledge, which may be acquired by the study of the\nannexed diagrams.\n\n[Illustration: Fig. CV.\n\nAnterior view of the regions of the body. 1. Region of the neck; 2.\nregion of the chest or thorax. Abdominal regions: 3. epigastric; 4.\numbilical; 5. hypogastric region. Regions of the upper extremities. 6.\nshoulder; 7. arm; 8. elbow; 9. fore-arm; 10. wrist; 11. ball of thumb;\n12. the axilla or armpit. Regions of the lower extremities: 13. thigh;\n14. knee; 15. leg; 16. ankle; 17. instep and foot.]\n\n[Illustration: Fig. CVI.\n\nPosterior view of the regions of the body: 18. region to the scapula;\n19. of the back; 20. of the loins; 21. of the hips; 22. of the ham; 23.\nof the calf of the leg; 24. of the heel and foot.]\n\n[Illustration: Fig. CVII.\n\nLateral view of the regions of the body: 25. arch of the foot.]\n\n[Illustration: Fig. CVIII.\n\nAnterior view of the situation of the more important internal organs:\n1. lungs, right and left; 2. heart; 3. line representing the edge of\nthe diaphragm; 4. liver; 5. stomach; 6. small intestines; 7. colon; 8.\nurinary bladder.]\n\n[Illustration: Fig. CIX.\n\nPosterior view of the situation of the more important internal organs:\n9. kidnies, right and left; 10. the course of the spinal cord.]\n\n[Illustration: Fig. CX.\n\nLateral view of the situation of the more important internal organs.]\n\n\n\n\nCHAPTER VI.\n\nOF THE BLOOD.\n\n  Physical characters of the blood: colour, fluidity,\n  specific gravity, temperature: quantity\u2014Process\n  of coagulation\u2014Constituents of the blood:\n  proportions\u2014Constituents of the body contained in the\n  blood\u2014Vital properties of the blood\u2014Practical applications.\n\n\n211. Supposing the human body to have been built up in the manner now\ndescribed, and to be in the full exercise of all its functions, the\nintegrity of its various structures is maintained, and their due action\nexcited by the blood. Out of this substance is formed the blandest\nfluid, as the milk, and the firmest solid, as the compact bone. The\nheart, capable of untiring action, as long as the blood is in contact\nwith its internal surface, becomes immovable soon after the supply of\nthis fluid is withdrawn; and in less than one minute from the time\nit ceases to flow in due quantity and of proper quality through the\nvessels of the brain, the eye is no longer capable of seeing, nor the\near of hearing, nor the brain of carrying on any intellectual operation.\n\n212. At the moment, and for some time after it has issued from its\nvessel, the appearance of the blood is that of a thick, viscid, and\ntenacious fluid; yet it is essentially a solid, composed of several\nsubstances, each possessing its own distinct and peculiar properties,\nthe relation and combination of which cannot be considered without\nexciting the feeling that our admiration of the structure of the animal\nframe ought not to be confined to the mechanism of its solid parts, but\nthat the whole is admirable, from the common material of which it is\ncomposed, to its most delicate and elaborate instrument.\n\n213. The colour of redness is universally associated with the idea of\nblood; but redness of colour is not essential to blood. There are many\nanimals with true, yet without red, blood; and there is no animal in\nwhich the blood is red in all the parts of its body. The blood of the\ninsect is transparent; that of the reptile is of a yellowish colour;\nthat of the fish, in the greater part of its body, is colourless. Even\nthe red blood of the human body is not equally red in every part of it,\nthere being two distinct systems of blood-vessels, distinguished from\neach other by carrying blood of different colours.\n\n214. In the state of health, the specific gravity of human blood, water\nbeing 1000, is 1080; from which standard it is capable of varying from\n1120, the maximum, to 1026, the minimum.\n\n215. The natural temperature of the human blood is 98\u00b0. From this it\nis capable of varying from 104\u00b0, the maximum, to 86\u00b0, the minimum;\nthese changes being always the effect of disease.\n\n216. It is estimated that the fluids circulating in the adult\nman amount to about fifty pounds; of these it is calculated that\ntwenty-eight consist of red blood.\n\n217. Fluid and homogeneous as the blood appears while flowing in its\nvessel, when a mass of it is collected and allowed to stand at rest, it\nsoon undergoes a very remarkable change. First, a thin film is formed\nupon its surface; this is followed by the conversion of the whole mass\ninto a soft jelly: this jelly separates into two portions, a fluid and\na solid portion. The solid portion again separates into two parts, into\na substance of a yellowish-white colour, occupying the upper surface,\nand into a red mass always found at the under surface.\n\n218. The process by which the constituents of the blood are thus\nspontaneously disunited, and afforded in a separate form, is\ndenominated COAGULATION; the fluid portion separated by the process is\ntermed the SERUM; the solid portion the COAGULUM or CLOT; the white\nsubstance forming the upper part of the clot, the FIBRIN; and the red\nmass forming the under part of it, the RED PARTICLES.\n\n219. Probably the process of coagulation commences the moment the\nblood leaves its living vessel. In three minutes and a half it is\nvisible to the eye; in seven minutes the mass is formed into a jelly;\nin from ten to twelve minutes the serum separates from the clot; in\nabout twenty the clot is divided into fibrin and red particles, when\nthe coagulation is complete; but occasionally the clot continues to\ngrow firmer and firmer for the space of twenty-four hours.\n\n220. As soon as the coagulation commences, and during all the time the\nblood preserves its heat, an aqueous vapour arises from it, termed\nthe HALITUS. The halitus consists of water holding in solution a\nsmall quantity of animal and saline matter, which communicate to it a\nf\u0153tid odour of a strong and peculiar nature, manifest on approaching\na slaughter-house, and still more manifest in the slaughter-house of\nhuman beings, a field of battle.\n\n221. During the process of coagulation, as in every other in which a\nfluid is converted into a solid, caloric is evolved.\n\n222. During the process of coagulation carbonic acid is also extricated.\n\n223. The process of coagulation affords three distinct substances,\nthe chief constituents of the blood, namely, serum, fibrin, and red\nparticles.\n\n224. The serum, the fluid portion of the blood, when obtained\nperfectly pure, is of a light straw colour, tinged with green.\nIts taste is saline, and its consistence adhesive. It is composed\nprincipally of water holding in solution animal and saline matter.\nThe animal matter gives it its adhesive consistence, and the saline\nits peculiar salt taste. The chief animal matter contained in it is\nthe proximate principle termed albumen, which may be separated from\nthe water that holds it in solution by the application of heat and\nby certain chemical agents. Heat being applied, when the temperature\nreaches 160\u00b0, fluid serum is converted into a white opaque solid\nsubstance of firm consistence. This is found to be albumen, which may\nbe also separated from the watery portion by the application of spirits\nof wine, acids, oxymuriate of mercury, and several other chemical\nsubstances. The quantity of albumen contained in 1000 parts of serum\nvaries from about 78, the maximum, to 58, the minimum.\n\n225. If the albumen yielded by the serum be subjected to pressure, or\nbe cut into small pieces, there flows from it a watery fluid which is\ntermed the serosity. In meat dressed for the table, the serum of the\nblood contained in the blood-vessels is converted by the heat into\nsolid albumen, from which, when cut, the serosity flows in the form of\ngravy.\n\n226. Besides albumen, serum holds in solution both a fatty and an oily\nmatter, in the proportion of about one part of each to 1000 parts of\nserum. The proportion of its saline substances is about ten in 1000\nparts. According to M. le Canu, who has made the most recent chemical\nanalysis of serum, 1000 parts contain, of\n\n  Water                                     906\u00b700\n  Albumen                                    78\u00b700\n  Animal matter, soluble in water\n    and alcohol                               1\u00b769\n  Albumen combined with soda                  2\u00b710\n  Crystallizable fatty matter                 1\u00b720\n  Oily matter                                 1\u00b700\n  Hydrochlorate of soda and\n    potash                                    6\u00b700\n  Subcarbonate and phosphate of\n    soda, and sulphate of potash              2\u00b710\n  Phosphate of lime, magnesia,\n    and iron, with subcarbonate\n    of lime and magnesia                       \u00b791\n  Loss                                        1\u00b700\n\n227. All the animal and saline matter held in solution in the serum\nbeing removed, the fluid that remains is water, the proportion of which\nin 1000 parts varies from 853, the maximum, to 779, the minimum.\n\n228. The second constituent of the blood, the fibrin, is the most\nessential portion of it, being invariably present, whatever other\nconstituent be absent. While circulating in the living vessel,\nfibrin is fluid and transparent; by the process of coagulation, it\nis converted into a solid and opaque substance of a yellowish white\ncolour, consisting of stringy fibres, disposed in stri\u00e6, which\noccasionally form a complete net-work (fig. CXI.). These fibres are\nexceedingly elastic. In their general aspect and their chemical\nrelations they bear a close resemblance to pure muscular fibre, that\nis, to muscular fibre deprived of its enveloping membrane and of its\ncolouring matter, and they form the basis of muscle. According to M.\nle Canu, the proportion of the fibrin varies from seven parts in 1000,\nthe maximum, to one part in 1000, the minimum, the medium of twenty\nexperiments being four parts in 1000.\n\n[Illustration: Fig. CXI.\n\nA portion of the fibrin of the blood, showing its fibrous structure and\nthe striated or net-like arrangement of its fibres.]\n\n229. The third constituent of the blood, the matter upon which its red\ncolour depends, though, as has been stated, entirely absent in certain\nclasses of animals, and in all animals in some parts of their body,\nseems to be essential, at least to the organic organs, whenever they\nperform their functions with a high degree of perfection. Thus in the\nlowest class of vertebrated animals, the fish, while the principal part\nof its body receives only a colourless fluid, its organic organs, as\nthe heart, the gills, the liver, are provided with red blood.\n\n230. The red matter, wherever present, is invariably heavier than\nthe fibrin, and consequently, during the process of coagulation, it\ngradually subsides to the lower surface, and is always found forming\nthe bottom of the clot. Its proportion to the other constituents varies\nvery remarkably, the maximum being 148, the minimum 68, and the medium\n108, in 1000 parts of blood.\n\n231. All observers are agreed that the red matter of the blood consists\nof minute particles, having a peculiar and definite structure; but in\nregard to the nature of that structure, there is considerable diversity\nof opinion, which is not wonderful, since the particles in question\nare so minute that they can be distinguished only by the microscope,\nand since, of all microscopical objects, they are perhaps the most\ndifficult to examine, because, being soft and yielding, their figure\nis apt to change, and because there is reason to suppose that their\nsubstance is not uniform in its refractive power.\n\n232. The earlier observers describe the red particles as being of\na globular figure, and accordingly name them globules. They conceive\nthat each globule consists of a central solid particle, enveloped in a\ntransparent vesicle. Recently, Sir Everard Home and Mr. Bauer in this\ncountry, and MM. Prevost and Dumas on the continent, have revived this\nopinion, and describe the red particle as consisting of a central solid\nwhite corpuscle contained in an external envelop of a red colour. When\nthe blood is observed with the microscope in a living animal, flowing\nin its vessels, only two substances can be distinguished, namely,\na transparent fluid and the red corpuscles. MM. Prevost and Dumas\ncontend that these two substances are the only component parts of the\nblood. When the blood coagulates, they conceive that the red envelop\nseparates from the central white corpuscle; that these white corpuscles\nunite together; that the aggregates resulting from this combination\nare disposed in the form of filaments, which filaments constitute the\nfibrin, while the red matter at the bottom of the clot is nothing but\nthe disintegrated envelops of the central particle. But this view is\nnot the common one. In general, physiologists conceive the fibrin to\nbe one constituent and the red particles to be another constituent of\nthe blood. Mr. Lister, who has successfully laboured to improve the\nmicroscope, and who, together with his friend Dr. Hodgkin, have very\ncarefully examined with their improved instrument the red particles,\ncontend that the figure of these bodies is not globular, although\nthey state that the instant the particles are removed from the living\nblood-vessels many things are capable of making them assume a globular\nappearance; such, for example, as the application of water. With a\nrapidity which, in spite of every precaution, the eye in vain attempts\nto follow, the particles change their real figure for a globular form\non the application of the smallest quantity of pure water; while,\nif the water contain a solution of saline matter, little alteration\nis occasioned in the figure of the particles. According to these\nobservers, the red particles are flattened cakes, having rounded and\nvery slightly thickened margins (fig. CXII. 1). The thickness of the\nmargin gives to both surfaces the appearance of a slight depression\nin the middle (fig. CXII. 1), so that the particles bear a close\nresemblance to a penny piece. There is no appearance of an external\nenvelop. The circular and flattened cake is transparent; when seen\nsingly it is nearly if not quite colourless (fig. CXII. 1); it assumes\na reddish tinge only when aggregated in considerable masses.\n\n[Illustration: Fig. CXII.\n\n1. A particle of the human blood as it appears when transparent and\nfloating; 2. the same dry, seen as opaque, illuminated by a leiberkuhn;\n3. the same as it appears when half the leiberkuhn is darkened; 4. a\nparticle of the frog's blood floating; 5. the same seen on its edge.\nAll the above objects are magnified 500 diameters[5].]\n\n233. The red particle of the human blood is circular (fig. CXII. 1, 2,\n3). It is circular also in all animals belonging to the class mammalia;\nbut in the three lower classes of vertebrated animals, the bird, the\nreptile, and the fish, it is elliptical (fig. CXII. 4, 5).\n\n234. The magnitude of the red particle of the human blood is variously\nestimated from the two-thousandth to the six-thousandth part of an inch\nin diameter. Bauer estimates it at the two-thousandth, Hodgkin and\nLister at the three-thousandth, Kater at the four-thousandth, Wollaston\nat the five-thousandth, and Young at the six-thousandth part of an\ninch. Its magnitude is uniformly the same in all individuals of the\nsame species, but differs exceedingly in the different classes. The\nelliptical particles are larger than the circular, but proportionally\nthinner; larger in fishes than in any other class of animals, and\nlargest of all in the skate.\n\n235. When perfect and entire, the red particles indicate a disposition\nto arrange themselves in a definite mode. They combine spontaneously\ninto columns of variable length (fig. CXIII.). In order to observe this\ntendency, a small quantity of blood, the moment it is taken from its\nliving vessel, should be placed between two strips of glass or covered\nwith a bit of talc and placed under the microscope. When thus arranged,\na considerable agitation at first takes place among the particles.\nAs soon as this motion subsides, the particles apply themselves to\neach other by their broad surfaces, and thus form piles or columns of\nConsiderable length (fig. CXIII.). The columns often again combine one\namong another, the end of one being attached to the side of another,\nsometimes producing very curious ramifications (fig. CXIII.). In\nlike manner, the elliptical particles apply themselves to each other\nby their broad surfaces, but they are not so exactly matched as the\ncircular, one particle partially overlapping another, so that they form\nless regular columns than the circular.\n\n[Illustration: Fig. CXIII.\n\nColumnar arrangement which the particles of the human blood assume\nimmediately after it is drawn from its vessel.]\n\n236. The red particles, as far as is known, constitute a distinct and\npeculiar form of animal matter: the red colour, according to some,\ndepending on an impregnation of iron; according to others, on an animal\nsubstance of a gelatinous nature.\n\n237. The exact proportion of the different substances contained in the\nblood, according to the most recent analysis of it, that by M. le Canu,\nis as follows, namely,\n\n  Water                                786\u00b7500\n  Albumen                               69\u00b7415\n  Fibrin                                 3\u00b7565\n  Colouring matter                     119\u00b7626\n  Crystallizable fatty matter            4\u00b7300\n    Oily matter                          2\u00b7270\n  Extractive matter, soluble in\n    alcohol and water                    1\u00b7920\n  Albumen combined with soda             2\u00b7010\n  Chloruret of sodium and potassium,\n    alkaline phosphate,\n    sulphate, and subcarbonates          7\u00b7304\n  Subcarbonate of lime and magnesia,\n    phosphates of lime,\n    magnesia and iron, peroxide\n    of iron                              1\u00b7414\n  Loss                                   2\u00b7586\n                                      --------\n                                      1000\u00b7\n\n238. From the results of this analysis it is manifest that all the\nproximate principles of which the different tissues are composed exist\nin the blood, namely, albumen, the proximate principle forming the\nbasis of membrane; fibrin, the proximate principle forming the basis\nof muscle; fatty matter, forming the basis of nerve and brain; and\nvarious saline and mineral substances, forming a large part of bone,\nand entering more or less into the composition of every fluid and solid.\n\n239. The blood, which contains all the proximate constituents of the\nbody, and which, by distributing them to the various tissues and\norgans, maintains their integrity and life, is itself alive. The\nvitality of the blood is proved,\u2014\n\n240. i. By its undergoing the process of death, which it does just as\nmuch as the heart or the brain, every time it is removed from the body.\nWhile flowing in its living vessel, the blood is permanently fluid.\nIts fluidity depends on a force of mutual repulsion exerted by its\nparticles on each other. That repulsive force is a vital endowment,\nprobably derived from the organic nerves so abundantly distributed\nto the inner coat of the blood-vessels. When this vital influence\nis withdrawn, which happens on the removal of the blood from its\nvessel, the mass is no longer capable of remaining fluid; the fibrin\nis converted into a solid; the red particles, instead of repelling,\nattract each other, forming the crude aggregate at the bottom of\nthe clot; coagulation is thus a process of death; its commencement\nindicates a diminution of the vital energy of the blood; during its\nprogress that energy is constantly growing less and less; the blood is\ndying; and when complete, the blood is dead.\n\n241. Hence in every state of the system in which the vital energy of\nthe blood is preternaturally increased, coagulation is proportionably\nslow; in every state in which its energy is diminished, coagulation\nis rapid. By copious and repeated blood-letting, the vital energy\nis rapidly exhausted. The effect of blood-letting on coagulation\nis determined by experiments instituted for the express purpose of\nascertaining it. Blood was received from a horse at four periods, about\na minute and a half intervening between the filling of each cup.\n\n                                      Minutes.   Seconds.\n\n  In cup No. 1. coagulation began in     11         10\n       \"     2.     \"     \"     \"        10          5\n       \"     3.     \"     \"     \"         9         55\n       \"     4.     \"     \"     \"         3         10\n\n242. In like manner three cups were filled with the blood of a sheep,\nat the interval of half a minute.\n\n                                      Minutes.   Seconds.\n\n  In cup No. 1. coagulation began in      2         10\n       \"     2.     \"     \"     \"         1         45\n       \"     3.     \"     \"     \"         0         55\n\nThe same result was obtained in blood taken from a human subject. A\npound and a half of blood was removed from the arm of a woman labouring\nunder fever, a portion of which, received into a tea-cup on the first\neffusion, remained fluid for the space of seven minutes; a similar\nquantity, taken immediately before tying up the arm, was coagulated\nin three minutes thirty seconds. These experiments demonstrate that\ncoagulation is rapid or slow as the vital energy of the blood is\nexhausted or unexhausted, or that in proportion to the degree of life\npossessed by the blood is the space of time it takes in dying.\n\n243. This result is referable to the principle already shown to be\ncharacteristic of living substance,\u2014namely, the power of resisting,\nwithin a certain range, the ordinary influence of physical agents.\nThe operation of this power is illustrated in a beautiful manner in\na series of experiments performed by Mr. Hunter on the egg and on\nblood. This physiologist exposed a live, that is, a fresh egg to the\ntemperature of the 17th and the 15th degrees of Fahrenheit; it took\nhalf an hour to freeze it. The egg was then thawed and exposed to 10\u00b0\nless cold, namely, to the 25th degree of Fahrenheit; it was now frozen\nin a quarter of an hour. A living egg and one that had been killed by\nhaving been first frozen and then thawed, were put together into a\nfreezing mixture at 15\u00b0: the dead was frozen twenty-five minutes sooner\nthan the living egg. The undiminished vitality of the fresh egg enabled\nit to resist the low temperature for the space of twenty-five minutes;\nthe vitality of the frozen egg having been destroyed, it yielded at\nonce to the influence of the physical agent. On subjecting blood to\nanalogous experiments, the result was found to be the same. Blood\nimmediately taken from the living vessel, and blood previously frozen\nand then thawed, being exposed to a freezing mixture, a much shorter\nperiod and a much less degree of cold were required to freeze the\nlatter than the former.\n\n244. ii. The vitality of the blood is proved by the change it\nundergoes in becoming a constituent part of an organized tissue.\nThe blood conveys to the several tissues the constituents of which\nthey are composed; each tissue selects from the mass of blood its\nown constituents and converts them into its own substance, in which\nconversion, since the blood always goes to the tissue in a fluid\nform, the blood must necessarily pass from a fluid into a solid. In\nthe vessels the vital endowment of the blood maintains it permanently\nfluid; in the structures the same power makes it and keeps it\nsolid. One and the same substance in one and the same body, in one\npart is always fluid, in another always solid; the fluid is every\nmoment passing into the solid and the solid into the fluid, without\nintermixture and without interference. Nothing analogous to this is\never witnessed in inorganic matter, in physical mechanism; it is\npeculiar to the organized body and distinctive of the mechanism of\nlife. Sometimes in physical mechanism we can perceive the mechanical\narrangements and distinctly trace them from beginning to end: in vital\nmechanism, even when we can discern the mechanical arrangements, we can\nseldom trace them beyond a step or two, and never from beginning to\nend; but arrangement and adaptation we know there must be in that which\ngoes beyond, no less than in that which keeps within, our perception,\nand we ought scarcely to question the existence of adjustments, because\nthey elude our sense, when probably the very reason why they do so is\nthat their delicacy and perfection immeasurably exceed any with which\nsense has made us acquainted.\n\n245. iii. The vitality of the blood is proved by the process of\norganization. We can trace only a few steps of this process, but these\nare sufficient to establish the point in question. Blood effused from\nliving vessels into the substance, or upon the surface of living\norgans, solidifies without losing vitality. If a clot of blood be\nexamined some time after it has thus become solid, it is found to\nabound with blood-vessels. Some of these vessels are obviously derived\nfrom the surrounding living parts. The minute vessels of these parts,\nas can be distinctly traced, elongate and shoot into the clot. The\nclot thus acquires blood-vessels of its own. By degrees a complete\ncirculation is established within it. The blood-vessels of the clot act\nupon the blood they receive just as the vessels of any other part act\nupon their blood, that is transform it into the animal matter it is\ntheir office to elaborate. In this manner a clot of blood is converted\ninto a component part of the body, and acquires the power of exercising\nits own peculiar and appropriate functions in the economy.\n\n246. But while, in this process, some of the vessels of the clot can\nbe distinctly traced from the surrounding living parts, others appear\nto have no communication with those parts, at all events no such\ncommunication can be traced. These vessels, the origin of which cannot\nbe found external to the clot, are supposed by some physiologists to\nbe formed within it. Within the living egg, during incubation, certain\nmotions or actions are observed spontaneously to arise, which terminate\nin the development of the chick. Analogous motions arising within the\nclot terminate, it is conceived, in the development of blood-vessels.\nAccording to this view, a simultaneous action takes place in the clot,\nand in the living part with which it is in contact; each shooting out\nvessels which elongate, approximate, unite, and thus establish a direct\nvital communication. Whether this view of the process of organization\nbe the correct one or not does not affect the present argument. It\nis certain that a clot of blood surrounded by living parts becomes\norganized; it is certain that no dead substance surrounded by living\nparts becomes organized; it follows that the blood possesses life.\n\n247. Health and life depend on the quantity, quality, and distribution\nof the blood. The chief source from which the blood itself is derived\nis the chyle: hence too much or too little food, or too great or too\nlittle activity of the organs that digest it, may render the quantity\nof the blood preternaturally abundant or deficient; or though there be\nneither excess nor deficiency in the quantity of nourishment formed,\nparts of the blood which ought to be removed may be retained, or\nparts which ought to be retained may be removed, and hence the actual\nquantity in the system may be superabundant or insufficient.\n\n248. The relative proportion of every constituent of the blood\nis capable of varying; and of course in the degree in which the\nhealthy proportion is deranged, the quality of the mass must undergo\na corresponding deterioration. The watery portion is sometimes so\ndeficient, that the mass is obviously thickened; while at other times\nthe fluid preponderates so much over the solid constituents, that the\nblood is thin and watery. The albumen, the quantity of which varies\nconsiderably even in health, in disease is sometimes twice as great,\nand at other times is less than half its natural proportion. In some\ncases the fibrin preponderates so much, that the coagulum formed by\nthe blood is exceedingly coherent, firm and dense; in other cases the\nquantity of fibrin is so small, that the coagulation is imperfect,\nforming only a soft, loose and tender coagulum, and in extreme cases\nthe blood remains wholly fluid. When the vital energy of the system\nis great, the red particles abound; when it is depressed, they are\ndeficient. In the former state, they are of a bright red colour; in\nthe latter, dusky, purple, or even black. When the depression of\nthe vital energy is extreme, the power of mutual repulsion exerted\nby the particles would seem to be so far destroyed as to admit of\ntheir adhering to each other partially in certain organs; while in\nother cases they seem to be actually disorganised, and to have their\nstructures so broken up, that they escape from the current of the\ncirculation as if dissolved in the serum, through the minute vessels\nintended only for the exhalation of the watery part of the blood.\nThis fearful change is conceived to have an intimate connexion with\na diminution of the proportion of the saline constituents. Out of\nthe body, as has been shown, the red particles change their figure\ninstantaneously, and are rapidly dissolved when in contact with\npure water; while they undergo little change of form if the water\nhold saline matter in solution. It would seem that one use of the\nsaline constituents of the blood is to preserve entire the figure and\nconstitution of the red particles. It is certain that any change in the\nproportion of the saline constituents produces a most powerful effect\non the condition of the red particles. It is no less certain that\nchanges do take place in the proportion of the saline constituents.\nIn the state of health, the taste of the blood is distinctly salt,\ndepending chiefly on the quantity of muriate of soda contained in\nit. In certain violent and malignant diseases, such, for example, as\nthe malignant forms of fever, and more especially that form of it\ntermed pestilential cholera, this salt taste is scarcely, if at all,\nperceptible; and it is ascertained that, in such cases, the proportion\nof saline matter is sensibly diminished.\n\n249. The quality of the blood may be also essentially changed\nby the disturbance of the balance of certain organic functions:\ndigestion, absorption, circulation, respiration, are indispensable\nto the formation of the blood and to the nourishment of the tissues.\nAbsorption, nutrition, secretion, circulation, render the blood impure,\neither by directly communicating to it hurtful ingredients, or by\nallowing noxious matters to accumulate in it, or by destroying the\nrelative proportion of its constituents. Organs are specially provided,\nthe main function of which is to separate and remove from the blood\nthese injurious substances. Organs of this class are called depurating,\nand the process they carry on is denominated that of depuration. The\nlungs, the liver, the kidneys, are depurating organs, and one result at\nleast of the functions they perform is the purification or depuration\nof the blood. If the lung fail to eliminate carbon, the liver bile,\nthe kidney urine, carbon, bile, urine, or at least the constituents\nof which these substances are composed, must accumulate in the blood,\ncontaminate it, and render it incapable of duly nourishing and\nstimulating the organs.\n\n250. But though the blood be good in quality and just in quantity,\nhealth and life must still depend upon its proper distribution. It\nmay be sent out to the system too rapidly or too slowly. It may be\ndistributed to different portions of the system unequally; too much may\nbe sent to one organ, and too little to another: consequently, while\nthe latter languishes, the former may be oppressed, overwhelmed or\nstimulated to violent and destructive action. In either case health is\ndisturbed and life endangered.\n\n251. Of the mode and degree in which food, air, moisture, temperature,\nrepletion, abstinence, exercise, indolence, influence the quantity,\nquality, and distribution of the blood; of the mode in which the\ncondition of the blood modifies the actions both of the organic and\nthe animal organs; of the reason why health and disease are wholly\ndependent on those states and actions, a clear and just conception\nmay be formed when the several functions have been described, and the\nprecise office of each is understood.\n\n\n\n\nCHAPTER VII.\n\nOF THE CIRCULATION.\n\n  Vessels connected with the heart: chambers of the\n  heart\u2014Position of the heart\u2014Pulmonic circle:\n  systemic circle\u2014Structure of the heart, artery, and\n  vein\u2014Consequences of the discovery of the circulation to the\n  discoverer\u2014Action of the heart: sounds occasioned by its\n  different movements\u2014Contraction: dilatation\u2014Disposition\n  and action of the valves\u2014Powers that move the blood\u2014Force\n  of the heart\u2014Action of the arterial tubes: the pulse:\n  action of the capillaries: action of the veins\u2014Self-moving\n  power of the blood\u2014Vital endowment of the capillaries:\n  functions\u2014Practical applications.\n\n\n252. The blood, being necessary to nourish the tissues and to\nstimulate the organs, must be in motion in order to be borne to them.\nAn apparatus is provided partly for the purpose of originating an\nimpelling force to put the blood in motion, and partly for the purpose\nof conveying the blood when in motion to the different parts of the\nbody.\n\n253. The heart is the impelling organ; the great vessels in immediate\nconnexion with it are the transmitting organs (fig. CXIV. 1, 2). The\nheart is divided into two sets of chambers (fig. CXIV. 3, 4, 10, 11),\none for the reception of the blood from the different parts of the body\n(fig. CXIV. 3, 10); the other for the communication of the impulse\nwhich keeps the blood in motion (fig. CXIV. 4, 11). The chamber which\nreceives the blood is termed an auricle (fig. CXIV. 3, 10), and is\nconnected with a vessel termed a vein (fig. CXIV. 1, 2, 9); that which\ncommunicates impulse to the blood is termed a ventricle (fig. CXIV. 4,\n11), and is connected with a vessel termed an artery (fig. CXIV. 7,\n12). The vein carries blood to the auricle; the auricle transmits it to\nthe ventricle; the ventricle propels it into the artery; the artery,\ncarrying it out from the ventricle, ultimately sends it again into the\nvein, the vein returns it to the auricle, the auricle to the ventricle,\nthe ventricle to the artery, and thus the blood is constantly moving in\na circle; hence the name of the process, the circulation of the blood.\n\n[Illustration: Fig. CXIV.\n\nView of the heart with its several chambers exposed, and the great\nvessels in connection with them. 1. The superior vena cava; 2. the\ninferior vena cava; 3. the chamber called the right auricle; 4. the\nchamber called the right ventricle; 5. the line marking the passage\nbetween the two chambers, and the points of attachment of one margin of\nthe valve; 6. the septum between the two ventricles; 7. the pulmonary\nartery arising from the right ventricle, and dividing at 8, into right\nand left for the corresponding lungs; 9. the four pulmonary veins\nbringing the blood from the lungs into 10, the left auricle; 11. the\nleft ventricle; 12. the aorta arising from the left ventricle, and\npassing down behind the heart to distribute blood, by its divisions and\nsubdivisions, to every part of the body.]\n\n254. In nourishing the tissues and stimulating the organs, the blood\nparts with its nutritive and stimulating constituents, and receives in\nreturn some ingredients which can no longer be usefully employed in the\neconomy, and others which are positively injurious. An apparatus is\nestablished for its renovation and depuration; this organ is termed the\nlung (fig. LIX. 5), and to this organ the blood must in like manner be\nconveyed. Thus the blood moves in a double circle, one from the heart\nto the body and from the body back to the heart, termed the systemic\ncircle; the other from the heart to the lung and from the lung back\nto the heart, termed the pulmonic circle. Hence in the human body the\nheart is double, consisting of two corresponding parts precisely the\nsame in name, in nature, and in office; the one appropriated to the\ngreater, or the systemic, and the other to the lesser, or the pulmonic\ncirculation (fig. CXIV.).\n\n255. There is a complete separation between these two portions of the\nheart (fig. CXIV. 6), formed by a strong muscular partition which\nprevents any communication between them except through the medium of\nvessels.\n\n256. The heart is situated between the two lungs (fig. LIX. 2, 5),\nin the lower and fore part of the chest, nearly in the centre, but\ninclining a little to the left side. Its position is oblique (fig.\nLIX. 2, 5). Its basis is directed upwards, backwards, and towards the\nright (fig. LIX. 2); its apex is directed downwards, forwards, and\ntowards the left, opposite to the interval between the cartilages\nof the fifth and sixth ribs (fig. LIX. 2). It is inclosed in a bag\ntermed the pericardium (fig. CXV.), which consists of serous membrane.\nThe pericardium is considerably larger than the heart, allowing\nabundant space for the action of the organ (fig. CXV.). One part of\nthe pericardium forms a bag around the heart (fig. CXV.); the other\npart is reflected upon the heart so as to form its external covering\n(fig. CXV.), and is continued for a considerable distance upon the\ngreat vessels that go to and from the heart in such a manner that this\nbag, like all the serous membranes, constitutes a shut sac. Both that\nportion of the pericardium which is reflected upon the heart, and that\nwhich forms the internal surface of the bag around it, is moistened\nduring life by a serous fluid, which, after death, is condensed into a\nsmall quantity of transparent water. That portion of the pericardium\nwhich rests on the diaphragm (fig. LXX. 1) is so firmly attached to it\nthat it cannot be separated without laceration, and by this attachment,\ntogether with the great vessels at its base, the heart is firmly held\nin its situation, although in the varied movements of the body it is\ncapable of deviating to a slight extent from the exact position here\ndescribed.\n\n[Illustration: Fig. CXV.\n\nView of the heart enveloped in its pericardium, the fore part of the\nlatter being cut open and reflected back.]\n\n257. When the interior of the heart is laid open there are brought\ninto view four chambers (fig. CXIV. 3, 4, 10, 11), two for each circle.\nThose belonging to the pulmonic circle are on the right (fig. CXIV. 3,\n4), those to the systemic on the left side of the body (fig. CXIV. 10,\n11); hence the terms right and left are applied to these respective\nparts of the heart.\n\n258. The veins which carry the blood to the right or the pulmonic\nchambers are two, one of which brings it from the upper, and the other\nfrom the lower parts of the body: the first is called the superior and\nthe second the inferior vena cava (fig. CXIV. 1, 2). Both pour their\nblood into the first chamber, termed the right auricle (fig. CXIV.\n3); from the right auricle the blood passes into the second chamber,\ndenominated the right ventricle (fig. CXIV. 4): from which springs\nthe artery which carries the blood from the heart to the lung, the\npulmonary artery (fig. CXIV. 7). This is the pulmonic circle. From\nthe lung the blood is returned to the heart by four veins, termed the\npulmonary veins (fig. CXIV. 9), which pour the blood into the third\nchamber of the heart, the left auricle (fig. CXIV. 10). From the left\nauricle it passes into the fourth chamber, the left ventricle (fig.\nCXIV. 11), from which springs the artery which carries out the blood\nto the system, termed the aorta (figs. CXIV. 12, and CXVII. 11). This\nis the systemic circle. In the system the minute branches of the aorta\nunite with the minute branches that form the ven\u00e6 cav\u00e6, which return\nthe blood to the right auricle of the heart, and thus the double circle\nis completed.\n\n259. The two chambers called the auricles occupy the basis of the\nheart (fig. CXIV. 3, 10). The right auricle is situated at the basis\nof the right ventricle (figs. CXIV. 3, and CXVI. 4). It is partly\nmembranous and partly muscular. At its upper and back part is the\nopening of the vena cava superior (fig. CXVI. 1), which returns the\nblood to the heart from the head, neck, and all the upper parts of the\nbody. At its lower part is the opening of the vena cava inferior (fig.\nCXVI. 2), which returns the blood from all the lower parts of the body.\n\n[Illustration: Fig. CXVI.\n\nView of the heart with the great vessels in connection with it, on the\nright side, its different chambers being laid open and its structure\nshown. 1. The vena cava superior; 2. the vena cava inferior; 3. cut\nedge of the right auricle turned aside to show, 4. the cavity of the\nright auricle into which the two ven\u00e6 cav\u00e6 pour the blood returned\nfrom all parts of the body; 5. hook suspending the reflected portion\nof the wall of the auricle; 6. the right ventricle; 7. cut edge of the\nwall of the ventricle, a portion of which has been removed to show 8.\nthe cavity of the ventricle; 9. situation of the opening between the\nauricle and ventricle, called the auricular orifice of the ventricle;\n10. valve placed between the auricle and ventricle, one margin being\nfirmly attached to the auriculo-ventricular opening in its entire\nextent, the other lying loose in the cavity of the ventricle; 11.\nprobe passed from the auricle into the ventricle underneath the valve,\nshowing the course of the blood from the former chamber to the latter;\n12. the column\u00e6 carne\u00e6 attached by one extremity to the walls of the\nventricle, the other extremity ending in tendinous threads attached to\nthe loose margin of the valve; 13. passage to the pulmonary artery;\n14. the three semilunar valves placed at the commencement of 15. the\npulmonary artery; 16. the two great branches into which the trunk of\nthe pulmonary artery divides, one branch going to each lung.]\n\n260. The auricle communicates with its corresponding ventricle by a\nlarge opening, termed the auricular orifice of the ventricle (figs.\nCXIV. 5, and CXVI. 9). All around the opening is placed a thin but\nstrong membrane (fig. CXVI. 10), one margin of which is firmly attached\nto the wall of the ventricle (figs. CXIV. 5, and CXVI. 9), while the\nother is free (fig. CXVI. 10). This membrane receives the name, and, as\nwill be seen immediately, performs the office of a valve.\n\n261. The ventricle is much thicker and proportionally stronger than the\nauricle (fig. CXVI. 3, 6). It is composed almost entirely of muscular\nfibre. Over nearly the whole extent of its internal surface are placed\nirregular masses of muscular fibres, many of which stand out from the\nwall of the ventricle like columns or pillars (fig. CXVI. 12); hence\nthey are called fleshy columns (column\u00e6 carne\u00e6). Some of these fleshy\ncolumns are adherent by one extremity to the wall of the ventricle,\nwhile the other extremity terminates in tendinous threads which are\nattached to the membrane that forms the valve (fig. CXVI. 12).\n\n262. From the upper and right side of this chamber springs the\npulmonary artery (fig. CXVI. 15); at the entrance of which are placed\nthree membranes of a crescent or semilunar shape, termed the semilunar\nvalves (fig. CXVI. 14).\n\n263. The structure of the left side of the heart is perfectly analogous\nto that of the right. Its auricle, like that on the left side, is\nplaced at the base of the ventricle (figs. CXIV. 10, and CXVII. 2), and\nlike it also is thin, being composed chiefly of membrane. At its upper\nand back part (figs. CXIV. 9, and CXVII. 1) are the openings of the\nfour pulmonary veins, two from the right, and two from the left lung.\n\n264. At the passage of communication between the left auricle and\nventricle is placed a valve analogous to that on the right side (fig.\nCXVII. 7).\n\n[Illustration: Fig. CXVII.\n\nView of the heart with the great vessels in connection with it, on the\nleft side, its chambers being laid open as in the preceding figure.\n1. The four pulmonary veins opening into, 2. the cavity of the left\nauricle; 3. the cut edge of the wall of the auricle; 4. the appendix\nof the auricle; 5. the cavity of the left ventricle; 6. the cut edge\nof the wall of the ventricle, the greater portion of the wall having\nbeen removed to show the interior of the chamber; 7. valve placed\nbetween the auricle and ventricle; 8. column\u00e6 carne\u00e6 terminating in\ntendinous threads attached to the loose margin of the valve; 9. probe\npassed underneath the valve and its tendinous threads, raising them\nfrom the wall of the ventricle similar to a refluent current of blood;\n10. passage to 11. the aorta; 12. two of the semilunar valves placed\nat the mouth of the aorta, the third having been cut away; 13. arch of\nthe aorta; 14. the three semilunar valves at the commencement of the\npulmonary artery seen in action, completely closing the mouth of the\nvessel.]\n\n265. The walls of the left ventricle are nearly as thick again as those\nof the right, and its fleshy columns are much larger and stronger. From\nthe upper and back part of this fourth chamber (fig. CXVII. 11) springs\nthe great systemic artery, the aorta, around the mouth of which are\nplaced three semilunar valves (fig. CXVII. 12), similar to those at the\nmouth of the pulmonary artery.\n\n266. The partition which divides the two sets of chambers from each\nother (fig. CXIV. 6) is wholly composed of muscular fibres, and is\ncalled the septum of the heart.\n\n267. The external surface of the heart is covered by a thin but\nstrong membrane continued over it from the pericardium. Between this\nmembranous covering and its fleshy substance is lodged, even when the\nbody is reduced to the greatest degree of thinness, a quantity of\nfat. Immediately beneath this fat are the fleshy fibres that compose\nthe main bulk of the organ. These fibres are arranged in a peculiar\nmanner. The arrangement is not perceptible when the heart is examined\nin its natural state, but after it has been subjected to long-continued\nboiling, which, besides separating extraneous matters from the fibres,\nhardens and loosens without displacing them, the manner in which they\nare disposed is manifest. Just at the point where the muscular fibres\nthat constitute the septum of the auricles are set upon those which\nform the septum of the ventricles, and parallel with the origin of the\naorta, the heart is not muscular but tendinous. The substance called\ntendon, it has been shown, is often employed in the body to afford\norigin or insertion to muscular fibres, performing, in fact, the\nordinary office of bone, and substituted for it in situations where\nbone would be inconvenient. From the tendinous matter just indicated\nmost of the fibres that constitute the muscular walls of the heart\ntake their origin. From this point the fibres proceed in different\ndirections: those which go to form the wall of the auricles ascend;\nthose which form the wall of the ventricles pursue an oblique course\ndownwards, and the arrangement of the whole is such, that a general\ncontraction of the fibres must necessarily bring all the parts of the\nheart towards this central tendinous point. The object and the result\nof this arrangement will be manifest immediately.\n\n268. The internal surface of the chambers of the heart, in its whole\nextent, is lined by a fine transparent serous membrane, which renders\nit smooth and moist; and, like all other organs which have important\nfunctions to perform, it is plentifully supplied with blood-vessels and\nnerves.\n\n269. Such is the structure of the organ that moves the blood. The\nartery, the tube that carries it out from the heart, is a vessel\ncomposed of three distinct layers of membrane superimposed one upon\nanother, and intimately united by delicate cellular tissue. These\nlayers are termed tunics or coats. The external coat (fig. CXVIII. 3),\nwhich is also called the cellular, consists of minute whitish fibres,\nwhich are dense and tough, and closely interlaced together in every\ndirection. They form a membrane of great strength, the elasticity of\nwhich, especially in the longitudinal direction, is such that, in\naddition to its other names, it has received that of the elastic coat.\n\n[Illustration: Fig. CXVIII.\n\nPortion of an artery, showing the several coats of which it is composed\nseparated from each other. 1. The internal or serous coat; 2. the\nmiddle or fibrous coat; 3. the external or cellular coat.]\n\n270. The middle or the fibrous tunic is composed of yellowish\nflattened fibres which pass in an oblique direction around the calibre\nof the vessel, forming segments of circles, which, uniting, produce\ncomplete rings (fig. CXVIII. 2). This tunic is thick, consisting of\nseveral layers of fibres which it is easy to peel off in succession.\nThey form a firm, solid, elastic, but, at the same time, brittle\nmembrane.\n\n271. The inner tunic, thin, colourless, nearly transparent, and\nperfectly smooth, is moistened by a serous fluid, and is thence called\nthe serous coat (fig. CXVIII. 1). To the naked eye it presents no\nappearance of fibres, yet notwithstanding its extreme delicacy, it is\nso strong that, after the other coats of the artery have been entirely\nremoved in a living animal, it is capable of resisting the impetus of\nthe circulation, and of preventing the dilatation of the artery. The\narteries themselves are supplied with arteries, vessels that nourish\ntheir tissues, and which are sent to them from neighbouring branches,\nseldom or never from the vessel itself to which they are distributed.\nEach individual part of an artery is supplied by its own appropriate\nvessels, which form but few communications above and below, so that\nif care be not taken in surgical operations to disturb these nutrient\narteries very little, the vessel will perish for want of sustenance.\n\n272. The vein, the tube that carries back the blood to the heart,\nis composed of the same number of tunics as the artery, which, with\nthe exception of the middle, are essentially the same in structure,\nbut they are all much thinner. The external tunic consists of a less\ndense and strong cellular membrane; the middle tunic, instead of being\nformed of elastic rings, is composed of soft and yielding fibres,\ndisposed in a longitudinal direction; while the inner coat, which is\nstill more delicate than that of the artery, is arranged in a peculiar\nmanner. The inner coat of most veins, at slight intervals, is formed\ninto folds (fig. CXX. 5), one margin of which is firmly adherent to\nthe circumference of the vessel, while the other margin is free and\nturned in the direction of the heart. These membranous folds are termed\nvalves. In all veins the diameter of which is less than a line the\nvalves are single; in most veins of greater magnitude they are placed\nin pairs, while in some of the larger trunks they are triple, and in\na few instances quadruple, and even quintuple. The veins, like the\narteries, are supplied with nutrient vessels and nerves.\n\n273. All the arteries of the body proceed from the two trunks already\ndescribed; that connected with the pulmonic circle, the pulmonary\nartery, and that connected with the systemic circle, the aorta. These\nvessels, as they go out from the heart and proceed to their ultimate\ntermination, are arborescent, that is, they successively increase in\nnumber and diminish in size, like the branches of a tree going off from\nthe trunk (fig. CXIX. 1, 2, 3). Each trunk usually ends by dividing\ninto two or more branches (fig. CXIX. 1, 2), the combined area of which\nis always greater than that of the trunk from which they spring, in\nthe proportion of about one and a half to one. As the branch proceeds\nto its ultimate termination it divides and subdivides, until at length\nthe vessel becomes so minute, that it can no longer be distinguished\nby the eye. These ultimate branches are called capillary vessels,\nfrom their hair-like smallness (fig. CXIX. 4); but this term does not\nadequately express their minuteness. It has been stated (234) that the\nred particle of the blood, at the medium calculation, is not more than\nthe three-thousandth part of an inch in diameter; yet vast numbers of\nthe capillary vessels are so small that they are incapable of admitting\none of these particles, and receive only the colourless portion of the\nblood.\n\n[Illustration: Fig. CXIX.\n\nView of the manner in which an artery divides and subdivides into its\nultimate branches. 1. Trunk of the artery; 2. large branches into which\nit subdivides; 3. small branches, successively becoming smaller and\nsmaller until they terminate in 4. the capillary branches.]\n\n274. Every portion of an artery, by reason of the elasticity of its\ncoats, preserves nearly a cylindrical form, and as the area of the\nbranches is greater than that of the trunks, the blood, in proceeding\nfrom the heart to the capillaries, though passing through a series of\ndescending cylinders, is really flowing through an enlarging space.\n\n275. The disposition of the veins, like that of the arteries, is\narborescent, but in an inverse order; for the course of the veins is\nfrom capillary vessels to visible branches, and from visible branches\nto large trunks (fig. CXX. 1, 2, 3). In every part of the body where\nthe capillary arteries terminate the capillary veins begin, and\nthe branches uniting to form trunks, and the small to form large\ntrunks, and the trunks always advancing towards the heart, and always\nincreasing in magnitude as they approach it, form at length the two\nveins which it has been stated (258) return all the blood of the body\nto the right auricle of the heart.\n\n[Illustration: Fig. CXX.\n\nView of the manner in which the minute branches of the vein unite to\nform the larger branches and the trunks. 1. Capillary venous branches;\n2. small branches formed by the union of the capillary; 3. larger\nbranches formed by the union of the smaller and gradually increasing in\nsize, to form the great trunk, 4. a portion of which is laid open to\nshow its inner surface and the arrangement of 5. the valves formed by\nits inner coat.]\n\n276. The veins are very much more numerous than the arteries, for\nthey often consist of double sets, and they are at the same time\nmore capacious and more extensible. Reckoning the whole of the blood\nat one-fifth of the weight of the body, it is estimated that, of\nthis quantity, about one-fourth is in the arterial and the remaining\nthree-fourths in the venous system. The combined area of the branches\nof the veins is much greater than that of the two trunks in which they\nterminate (fig. CXX. 1, 2, 3, 4): the blood, therefore, in returning to\nthe heart, is always flowing from a large into a smaller space.\n\n277. The divisions and subdivisions of the artery freely communicate\nin all parts of the body by means of what are called anastomosing\nbranches, and this communication of branch with branch and trunk with\ntrunk is termed anastomosis. The same intercommunication, but with\nstill greater freedom and frequency, takes place among the branches\nof veins. In both orders of vessels the communication is frequent in\nproportion to the minuteness of the branch and its distance from the\nheart. It is also more frequent in proportion as a part is exposed\nto pressure; hence the minute arteries and veins about a joint are\ndistinguished for the multitude of their anastomosing branches; and\nabove all, it is frequent in proportion to the importance of the organ;\nhence the most remarkable anastomosis in the body is in the brain. By\nthis provision care is taken that no part be deprived of its supply of\nblood; for if one channel be blocked up, a hundred more are open to the\ncurrent, and the transmission of it to any particular region or organ\nby two or more channels, instead of through one trunk, is a part of the\nsame provision. Thus the fore-arm possesses four principal arteries\nwith corresponding veins, and the brain receives its blood through four\ntotally independent canals[6].\n\n278. That the blood is really a flowing stream, and that it pursues the\ncourse described (258), is indubitable. For,\n\n(1.) With the microscope, in the transparent parts of animals, the\nblood can be seen in motion (fig. CXXI.); and if its course be\nattentively observed, its route may be clearly traced.\n\n[Illustration: Fig. CXXI.\n\nView of the circulation of the blood as seen under the microscope in\nthe web of the frog's foot.]\n\n(2.) The membranes termed valves are so placed as to allow of the\nfreest passage to the blood in the circle described, while they either\naltogether prevent or exceedingly impede its movement in any other\ndirection.\n\n(3.) The effect of a ligature placed around a vein and an artery, and\nof a puncture made above the ligature in the one vessel and below it in\nthe other, demonstrate both the motion of the blood and the course of\nit. When a ligature is placed around a vein, that part of the vessel\nwhich is most distant from the heart becomes full and turgid on account\nof the accumulation of blood in it; while the part of the vessel which\nis between the ligature and the heart becomes empty and flaccid,\nbecause it has carried on its contents to the heart, and it can receive\nno fresh supply from the body. When, on the contrary, a ligature is\nplaced around an artery, that portion of the vessel which lies between\nthe ligature and the heart becomes full and turgid, and the other\nportion empty and flaccid. This can only be because the contents of\nthe two vessels move in opposite directions,\u2014from the heart to the\nartery, from the artery to the vein, and from the vein to the heart.\nAt the same time, if the vein be punctured above the ligature, there\nwill be little or no loss of blood; while if it be punctured below\nthe ligature, the blood will continue to flow until the loss of it\noccasions death, which could not be unless the blood were in motion,\nnor unless the direction of its course were from the artery to the vein\nand from the vein to the heart.\n\n(4.) If fluids be injected into the veins or arteries, whether of the\ndead or of the living body, they readily make their way and fill the\nvessels, if thrown in the direction stated to be the natural course\nof the circulation; but they are strongly resisted if forced in the\nopposite direction.\n\n279. Such is the description, and with the exception of the first\nproof, such the evidence of the circulation of the blood in the\nhuman body, pretty much as it was given by the discoverer of it, the\nillustrious Harvey. Before the time of Harvey, a vague and indistinct\nconception that the blood was not without motion in the body had been\nformed by several anatomists. It is analogous to the ordinary mode\nin which the human mind arrives at discovery (chap. iii., p. 103),\nthat many minds should have an imperfect perception of an unknown\ntruth, before some one mind sees it in its completeness and fully\ndiscloses it. Having, about the year 1620, succeeded in completely\ntracing the circle in which the blood moves, and having at that\ntime collected all the evidence of the fact, with a rare degree of\nphilosophical forbearance, Harvey still spent no less than eight years\nin re-examining the subject, and in maturing the proof of every point,\nbefore he ventured to speak of it in public. The brief tract which at\nlength he published was written with extreme simplicity, clearness,\nand perspicuity, and has been justly characterised as one of the most\nadmirable examples of a series of arguments deduced from observation\nand experiment that ever appeared on any subject.\n\n280. Cotemporaries are seldom grateful to discoverers. More than one\ninstance is on record in which a man has injured his fortune and lost\nhis happiness through the elucidation and establishment of a truth\nwhich has given him immortality. It may be that there are physical\ntruths yet to be brought to light, to say nothing of new applications\nof old truths, which, if they could be announced and demonstrated\nto-day, would be the ruin of the discoverer. It is certain that there\nare moral truths to be discovered, expounded, and enforced, which, if\nany man had now penetration enough to see them, and courage enough to\nexpress them, would cause him to be regarded by the present generation\nwith horror and detestation. Perhaps, during those eight years of\nre-examination, the discoverer of the circulation sometimes endeavoured\nin imagination to trace the effect which the stupendous fact at the\nknowledge of which he had arrived would have on the progress of his\nfavourite science; and, it may be, the hope and the expectation\noccasionally arose that the inestimable benefit he was about to confer\non his fellow men would secure to him some portion of their esteem\nand confidence. What must have been his disappointment when he found,\nafter the publication of his tract, that the little practice he had\nhad as a physician, by degrees fell off. He was too speculative,\ntoo theoretical, not practical. Such was the view taken even by his\nfriends. His enemies saw in his tract nothing but indications of a\npresumptuous mind that dared to call in question the revered authority\nof the ancients; and some of them saw, moreover, indications of a\nmalignant mind, that conceived and defended doctrines which, if not\nchecked, would undermine the very foundations of morality and religion.\nWhen the evidence of the truth became irresistible, then these persons\nsuddenly turned round and said, that it was all known before, and\nthat the sole merit of this vaunted discoverer consisted in having\ncirculated the circulation. The pun was not fatal to the future fame of\nthis truly great man, nor even to the gradual though slow return of the\npublic confidence even during his own time; for he lived to attain the\nsummit of reputation.\n\n281. It is then indubitably established that the whole blood of the\nbody in successive streams is collected and concentrated at the heart.\nThe object of the accumulation of a certain mass of it at this organ\nis to subject it to the action of a strong muscle, and thereby to\ndetermine its transmission with adequate force and precision through\nthe different sets of capillary vessels.\n\n282. In the accomplishment of this object the heart performs a twofold\naction; that of contraction and that of dilatation. The auricles\ncontract and thereby diminish their cavities, then dilate and thereby\nexpand them, and the one action alternates with the other. There is the\nlike alternate contraction and dilatation of the ventricles. The first\naction is termed systole, the second diastole, and both are performed\nwith force.\n\n283. When the heart is laid open to view in a living animal, and its\nmovements are carefully observed, it is apparent that the two auricles\ncontract together; that the two ventricles contract together; that\nthese motions alternate with each other, and that they proceed in\nregular succession. The interval between these alternate movements is,\nhowever, exceedingly short, and can scarcely be perceived when the\nheart is acting with full vigour; but it is evident when its action is\nsomewhat languid.\n\n284. When the ventricles contract, the apex of the heart is drawn\nupwards, and at the same time raised or tilted forwards. It is during\nthis systole of the ventricles, and in consequence of this result of\ntheir action, that the apex of the heart gives that impulse against the\nwalls of the chest which is felt in the natural state between the fifth\nand sixth ribs, and which just perceptibly precedes the pulse at the\nwrist.\n\n285. When the ear is applied to the human chest, over the situation of\nthe heart, a dull and somewhat prolonged sound is heard, which precedes\nand accompanies the impulse of the heart against the chest. This dull\nsound is immediately succeeded by a shorter and sharper sound: after\nthis there is a short pause; and then the dull sound and impulse are\nagain renewed. The duller sound and stronger impulse are ascribed to\nthe contraction of the ventricles, and the sharper sound and feebler\nimpulse to that of the auricles.\n\n286. The movement of the heart is effected by the contraction of its\nmuscular fibres. Those fibres rest, as upon a firm support, on the\ntendinous matter to which they are attached, from which they diverge,\nand towards which their contraction must necessarily bring all the\nparts of the heart (267). The result of their contraction is the\npowerful compression of all the chambers of the heart, and thereby the\nforcible ejection of their contents through the natural openings.\n\n287. But the chambers, alternately with forcible contraction, perform\nthe action of forcible dilatation. This movement of dilatation is\neffected by the reaction of the elasticity of the tendinous matter on\nwhich the muscular fibres are supported (267). This highly elastic\nsubstance, by the contraction of the fibres, is brought into a state of\nextreme tension. The contraction of the fibres ceasing, that moment the\ntense tendon recoils with a force exactly proportionate to the degree\nof tension into which it had been brought. Thus the very agent that is\nemployed forcibly to close the chamber is made the main instrument of\nsecuring its instantaneous re-opening. A vital energy is appointed to\naccomplish what is indispensable, and what nothing else can effect,\nthe origination of a motive power; a physical agent is conjoined to\nperform the easier task to which it is competent; and the two powers,\nthe vital and the physical, work in harmony, each acting alternately,\nand each, with undeviating regularity and unfailing energy, fulfilling\nits appropriate office.\n\n288. When the chambers of the heart which open into each other, and\nwhich as freely communicate with the great vessels that enter and\nproceed from them, are forcibly closed, and the blood they contain is\nprojected from them, how is one uniform forward direction given to the\ncurrent? Why, when the right ventricle contracts, is the blood not sent\nback into the right auricle, as well as forward into the pulmonary\nartery? There is but one mode of preventing such an event, which is to\nplace a flood-gate between the two chambers; and there a flood-gate\nis placed, and that flood-gate is the valve. As long as the blood\nproceeds onwards in the direct course of the circulation, it presses\nthis membrane close to the side of the heart, and thereby prevents it\nfrom occasioning any impediment to the current. When, on the contrary,\nthe blood is forced backwards, and attempts to re-enter the auricle,\nbeing of course driven in all directions, some of it passes between the\nwall of the ventricle and the valve. The moment it is in this situation\nit raises up the valve, carries it over the mouth of the passage, and\nshuts up the channel. There cannot be a more perfect flood-gate.\n\n289. This is beautiful mechanism; but there is another arrangement\nwhich surpasses mere mechanism, however beautiful. It has been shown\n(260) that one edge of the membrane that forms the valve is firmly\nadherent to the wall of the ventricle, while the other edge, when not\nin action, appears to lie loosely in the ventricle (fig. CXVI. 10).\nWere this edge really loose the refluent current would carry it back\ncompletely into the auricle, and so counteract its action as a valve;\nbut it is attached to the tendinous threads proceeding from the fleshy\ncolumns that stand along the wall of the ventricle (fig. CXVI. 12). By\nthese tendinous threads, as by so many strings, the membrane is firmly\nheld in its proper position (fig. CXVI. 10, 12); and the refluent\ncurrent cannot carry it into the auricle. Thus far the arrangement is\nmechanical. But each of these fleshy columns is a muscle, exerting\na proper muscular action. Among the stimulants which excite the\ncontractility of the muscular fibre, one of the most powerful is\ndistension. The refluent current distends the membrane; the distension\nof the membrane stretches the tendinous threads attached to it; the\nstretching of its tendinous threads stretches the fleshy column; by\nthis distension of the column it is excited to contraction; by the\ncontraction of the column its thread is shortened; by the shortening\nof the thread the valve is tightened, and that in the exact degree\nin which the thread is shortened. So, the greater the impetus of the\nrefluent blood, the greater the distension of the membrane; and the\ngreater the distension of the membrane, the greater the excitement of\nthe fleshy column; the greater the energy with which it is stimulated\nto act, the greater, therefore, the security that the valve will be\nheld just in the position that is required, with exactly the force that\nis needed. Here, then, is a flood-gate not only well constructed as far\nas regards the mechanical arrangement, but so endowed as to be able to\nact with additional force whenever additional force is requisite; to\nput forth on every occasion, as the occasion arises, just the degree of\nstrength required, and no more.\n\n290. The contraction of the heart is the power that moves the blood;\nand this contraction generates a force which is adequate to impel it\nthrough the circle. From experiments performed by Dr. Hales it appears\nthat if the artery of a large animal, such as the horse, be made to\ncommunicate with an upright tube, the blood will ascend in the tube to\nthe height of about ten feet above the level of the heart, and will\nafterwards continue there rising and falling a few inches with each\npulsation of the heart. In this animal, then, the heart acts with a\nforce capable of maintaining a column of ten feet. Now a column of ten\nfeet indicates a pressure of about four pounds and a half in a square\ninch of surface. Suppose the human heart to be capable of supporting\na column of blood eight feet high, this will indicate a pressure of\nfour pounds to the square inch; but the left ventricle of the heart,\nwhile it injects its column of blood into the aorta, has to overcome\nthe inertia of the quantity of blood projected; of the mass already\nin the artery, and of the elasticity of the vessel yielding to a\nmomentary increase of pressure: it is probable, therefore, that the\nheart acts with a force of six pounds on the inch. The left ventricle,\nwhen distended, has about ten square inches of internal surface;\nconsequently the whole force exerted by it may be about sixty pounds.\nAccording to the calculation of Hales, it is fifty-one and a half.\nNow, it is proved by numerous experiments, that, after death, a slight\nimpulse with the syringe, certainly much less than that which is acting\nupon the blood in the same artery during life, is sufficient to propel\na solution of indigo, or fresh drawn blood, from a large artery into\nthe extreme capillary. If, therefore, after death, a slight force will\nfill the capillaries, a force during life equal to sixty pounds must be\nadequate to do so.\n\n291. The heart, with a force equal to the pressure of sixty pounds,\npropels into the artery two ounces of blood at every contraction. It\ncontracts four thousand times in an hour. There passes through the\nheart, therefore, every hour, eight thousand ounces or seven hundred\npounds of blood. It has been stated (216) that the whole mass of blood\nin an adult is about twenty-eight pounds: on an average the entire\ncirculation is completed in two minutes and a half; consequently a\nquantity of blood equal to the whole mass passes through the heart\nfrom twenty to twenty-four times in an hour. But though the average\nspace of time requisite to accomplish a complete circulation may be\ntwo minutes and a half, yet when a stream of blood leaves the heart,\ndifferent portions of it must finish their circle at very different\nperiods, depending in part upon the length of the course which they\nhave to go, and in part upon the degree of resistance that obstructs\ntheir passage. A part of the stream, it is obvious, finishes its course\nin circulating through the heart itself; another portion takes a longer\ncircuit through the chest; another extends the circle round the head;\nand another visits the part placed at the remotest distance from the\ncentral moving power. Such is the velocity with which the current\nsometimes goes, that, in the horse, a fluid injected into the great\nvein of the neck, on one side, has been detected in the vein on the\nopposite side, and even in the vein of the foot, within half a minute.\n\n292. It has been shown (282) that the different chambers of the\nheart have a tendency to perform their movements in a uniform manner,\nand in a successive order; that they contract and dilate in regular\nalternation, and at equal intervals; but, moreover, they continue\nthese movements equally without rest and without fatigue. On go the\nmotions, night and day, for eighty years together, at the rate of\na hundred thousand strokes every twenty-four hours, alike without\ndisorder, cessation, or weariness. The muscles of the arm tire after\nan hour's exertion, are exhausted after a day's labour, and can by no\neffort be made to work beyond a certain period. There is no appreciable\ndifference between the muscular substance of the heart and that of the\narm. It is true that the heart is placed under one condition which\nis peculiar. Muscles contract on the application of stimuli; and\ndifferent muscles are obedient to different stimuli,\u2014the voluntary\nmuscles to the stimulus of volition, and the heart to that of the\nblood. The exertion of volition is not constant, but occasional; the\nmuscle acts only when it is excited by the application of its stimulus:\nhence the voluntary muscle has considerable intervals of rest. The\nblood, on the contrary, is conveyed to the heart without ceasing, in a\ndeterminate manner, in a successive order; and this is the reason why\nthrough life its action is uniform: it uniformly receives a due supply\nof its appropriate stimulus. But why it is unwearied, why it never\nrequires rest, we do not know. We know the necessities of the system\nwhich render it indispensable that it should be capable of untiring\naction, for we know that the first hour of its repose would be the\nlast of life; but of the mode in which this wonderful endowment is\ncommunicated, or of the relations upon which it is dependent, we are\nwholly ignorant.\n\n293. The force exerted by the heart is vital. It is distinguished from\nmechanical force in being produced by the very engine that exerts it.\nIn the best-constructed machinery there is no real generation of power.\nThere is merely concentration and direction of it. In the recoil of the\nspring, in the reaction of condensed steam, the energy of the expansive\nimpulse is never greater than the force employed to compress or\ncondense, and the moment this power is expended all capacity of motion\nis at an end. But the heart produces a force equal to the pressure of\nsixty pounds by the gentlest application of a bland fluid. Here no\nforce is communicated to be again given out, as in every mechanical\nmoving power; but it is new power, power really and properly generated;\nand this power is the result of vital action, and is never in any case\nthe result of action that is not vital.\n\n294. The heart projects the blood with a given force into the arterial\ntubes. The arteries in the living body are always filled to distension,\nand somewhat beyond it, by the quantity of blood that is in them. It\nhas been shown that the elasticity of their coats is such as to give\nto them, even after death, the form of open hollow cylinders (274).\nDuring life they are kept in a state of distension by the quantity of\nblood they contain. By virtue of their elasticity they react upon\ntheir contents with a force exactly proportioned to the degree of their\ndistension, that is, with a force at least adequate to keep them always\nopen and rigid.\n\n295. These open and rigid tubes, already filled to distension, and\nsomewhat beyond it, receive at every contraction of the heart a\nforcible injection of a new wave of blood. The first effect of the\ninjection of this new wave into a tube previously full to distension,\nis to cause the current to proceed by jerks or jets, each jerk or\njet corresponding to the contraction of the heart. And, accordingly,\nby this jet-like motion, the flow of the blood in the artery is\ndistinguished from that in the vein, in which latter vessel the current\nis an equal and tranquil stream.\n\n296. The second effect of this new wave is to occasion some further\ndistension of the already distended artery, and accordingly, when\nthe vessel is exposed in a living animal, and its action carefully\nobserved, a slight augmentation of its diameter is distinguishable at\nevery contraction of the heart. This new wave while it distends must at\nthe same time slightly elongate the vessel; cause its straight portions\nto bend a little, and its curved portions to bend still more; and,\nconsequently, in some situations, to lift it a little from its place,\ngiving it a slight degree of locomotion;\u2014and these two causes combined\nproduce the pulse. When the finger is pressed gently on an artery, at\nthe instant of the contraction of the heart, the vessel is felt to\nbound against the finger with a certain degree of force: this, as just\nstated, is owing to a slight distension of the vessel by the new wave\nof blood, together with a slight elongation of it, and a gentle rising\nfrom its situation.\n\n297. The blood, in flowing through the arterial trunks and branches\nto the capillaries, through the arterial to the venous capillaries, and\nthrough the venous branches and trunks back to the heart, is exposed\nto numerous and powerful causes of retardation: such, for example,\nas the friction between the blood and the sides of the vessels, the\nnumerous curves and angles formed by the branches in springing from the\ntrunks, the tortuous course of the vessels in many parts of the body,\nand the increasing area of the arterial branches as they multiply and\nsubdivide. Yet the extraordinary fact has been recently discovered,\nthat the blood moves with the same momentum or force in every part of\nthe arterial system, in the aorta, in the artery in the neck which\ncarries the blood to the head (the carotid artery), in the artery of\nthe arm (the humeral artery), in the artery of the lower extremity\n(the femoral artery); in a word, in the minute and remote capillary,\nand in the large trunk near the heart. Having contrived an instrument\nby which the force of the blood as it flows in its vessel could be\naccurately indicated by the rise of mercury in a tube, M. Poiseuille\nfound that the elevation of the mercury is uniformly the same in the\ndifferent arteries of the same animal, whatever the size of the artery\nand its distance from the heart. This tube was inserted, for example,\ninto the common carotid artery of a horse: the diameter of the vessel\nwas 34/100ths of an inch; its distance from the heart was thirty-nine\ninches; the height to which the mercury rose in the graduated tube was\naccurately marked. The tube was then inserted into a muscular branch of\nthe artery in the thigh: the diameter of this vessel was 7/100ths of an\ninch, and its distance from the heart 67\u00bd inches. According to the mean\nof nine observations, the mercury rose in both tubes to precisely the\nsame elevation. Here is another instance of the beautiful adjustments\neverywhere established in the living economy. The blood is sent by a\nliving engine, moving under laws peculiar to the state of life, into\nliving vessels, which in their turn acting under laws peculiar to the\nstate of life, so accommodate themselves to the current as absolutely\nto offer no resistance to its progress; so accommodate themselves to\nthe moving power, as completely and everywhere to obviate the physical\nimpediments to motion inseparable from inorganic matter.\n\n298. That the arterial tubes do possess and exert a truly vital power,\nmodifying the current of the blood they contain, is indubitably\nestablished.\n\n1. If in a living animal the trunk of an artery be laid bare, the mere\nexposure of it to the atmospheric air causes it to contract to such a\ndegree, that its size becomes obviously and strikingly diminished. This\ncan result only from the exertion of a vital property, for no dead tube\nis capable in such a manner of diminishing its diameter.\n\n2. If during life an artery be opened and the animal be largely bled,\nthe arteries become progressively smaller and smaller as the quantity\nof blood in the body diminishes. If the bleeding be continued until the\nanimal dies, and the arteries of the system be immediately examined,\nthey are found to be reduced to a very small size; if again examined\nsome time after death, they are found to have become larger, and they\ngo on growing successively larger and larger until they regain nearly\ntheir original magnitude, which they retain until they are decomposed\nby putrefaction.\n\n3. M. Poiseuille distended with water the artery of an animal just\nkilled. This water was urged by the pressure of a given column of\nmercury. The force of the reaction of the artery was now measured by\nthe height of a column of mercury which the water expelled from the\nartery could support. It was found that the artery reacted with a\nforce greater than that employed to distend it, and greater than the\nsame artery could exert some time after death; but since mechanical\nreaction can never be greater than the force previously exerted upon\nit (293), it follows that the excess of the reaction indicated in this\ncase was vital.\n\n4. If an artery be exposed and a mechanical or chemical stimulus be\napplied to it, its diameter is altered, sometimes becoming larger and\nsometimes smaller, according to the kind of agent employed.\n\n299. Any one of these facts, taken by itself, affords a demonstration\nthat the arterial trunks and branches are capable of enlarging and\ndiminishing their diameter by virtue of a vital endowment. There is\ncomplete evidence that the exertion of this vital power on the part\nof the arterial trunk is not to communicate to the blood the smallest\nimpulsive force; the engine constructed for the express purpose of\nworking the current generates all the force that is required; but the\nlabour of the engine is economized by imparting to the tubes that\nreceive the stream a vital property, by which they wholly remove the\nphysical obstructions to its motion.\n\n300. Driven by the heart through the arterial branches into the\ncapillaries, the blood courses along these minute vessels urged by the\nsame power. The most careful observers, from Haller and Spalanzani\ndown to the present time, concur in stating that the pulsatory\nmovement communicated by the heart to the blood in the great arteries\nis distinctly visible under the microscope in the capillaries. \"I\nhave often observed in frogs and tadpoles, and once in the bat,\" says\nWedemeyer, \"that when the circulation was becoming feeble, the blood\nin the finest capillaries advanced by jerks, corresponding with the\ncontractions of the heart. I remarked the same appearance in the fine\nveins several times in the toad and tadpole, and once in the frog.\" If\nan experimenter so dispose the circulation of the limb of an animal\nthat the flow of blood be confined to the branches of a single artery,\nand a corresponding vein, it is found that the blood stagnates in the\nvein whenever the current in the artery is stopped by a ligature, but\nno sooner is the ligature removed from the artery, than the blood\nbegins again to flow freely along the vein, the capillaries of the\nartery which have to send on the current to those of the vein being\nnow again within the influence of the heart. And if the impulse of\nthe heart be removed from the capillary system, by placing a ligature\naround the aorta, the capillary circulation is uniformly and completely\nstopped.\n\n301. It was found by Dr. Hales, that, under ordinary circumstances,\nthe blood rises in a tube connected with a vein to the height only of\nsix inches, while it has been shown (290) that in the artery it ascends\nas high as ten feet. This prodigious difference between the venous and\nthe arterial tension led to the conclusion that the impulsive force of\nthe heart was all but exhausted before the blood reached the veins, and\nset physiologists on the search for other powers to carry on the venous\ncirculation. It was overlooked that the blood has an open and ready\nescape from the great trunks of the veins through the right chambers of\nthe heart, and that in consequence of this free escape of their fluid,\nthese vessels indicate no greater tension than is just sufficient to\nlift the blood to the heart, and to overcome friction[7]. M. Magendie\nhaving laid bare the chief artery and vein of a living limb, and having\nraised the vessels in such a manner that he could place a ligature\naround the former, without including the latter, found that the flow\nof blood from a puncture made below a ligature on the vein, was rapid\nor slow, according as the heart was allowed to produce a greater or\nless degree of tension in the artery, which tension was regulated by\ncompressing the artery between the fingers. After a similar preparation\nof a limb, a ligature was placed around the vein; a tube was then\ninserted into it; it was found that the blood ascended in the tube from\nthe obstructed vein just as high as from the artery.\n\n302. Thus we are able to trace the action of the heart from the\nbeginning to the end of the circle. Of this circle it is the sole\nmoving power; but it is a living engine acting in combination with\nliving vessels. The force it exerts is a vital force, economized by the\nagency of a vital property communicated to the vessels, by virtue of\nwhich they spontaneously and completely remove all physical obstruction\nto the progress of the stream through its channels.\n\n303. Some German physiologists of great eminence, after a careful and\npatient observation of the blood, have satisfied themselves that in\naddition to the contraction of the heart, it is necessary to admit a\nsecond original and independent motive force, namely, a self-moving\npower inherent in the particles of the blood itself. The blood we\nknow is a living substance. No reason can be assigned why the power\nof originating motion should not be communicated to such a substance\nas well as to the muscular fibre, of which, indeed, one constituent\nof the blood affords the basis. Such a power, if found to be inherent\nin the particles of the blood, would explain some phenomena connected\nwith the circulation not yet clearly elucidated; but the proof of the\nself-moving power of the blood does not yet seem to be complete. It\nis, however, impossible to explain the phenomena of the circulation,\nor to obtain a satisfactory view of some of the other functions of the\neconomy, without supposing the particles of the blood to be endowed\nwith a vital power of repulsion, in consequence of which they are\nprevented from uniting when in contact, and the fluidity of the mass is\nmaintained.\n\nIn this account of the powers that move the blood, no notice has been\ntaken of the physical agents supposed to act as auxiliaries to the\nheart, in carrying on the circulation, such as the suction power of the\nthorax, and of the auricles of the heart, and the capillary attraction\nof the vessels; because, without questioning the existence of such\nagents, or denying that advantage may be taken of them, it seems pretty\nclear that their influence is but trivial, and they assumed importance\nonly when the vital endowments of the tissues were not well understood.\n\n304. The ultimate end for which the apparatus of the circulation is\nconstructed, and for which all its action is exerted, is to convey\narterial blood to the capillary arteries. These vessels are totally\ndistinct in structure and in office from the larger arterial tubes. All\nthe tunics of these minute vessels diminish in thickness and strength\nas the tubes lessen in size, but more especially the middle or the\nfibrous coat; which, according to Wedemeyer, may still be distinguished\nby its colour in the transverse section of any vessel whose internal\ndiameter is not less than the tenth of a line; but that it entirely\ndisappears in vessels too small and too remote to receive the wave of\nblood in a manifest jet. But while the membranous tunics diminish,\nthe nervous filaments distributed to them increase: the smaller and\nthinner the capillary, the greater the proportionate quantity of its\nnervous matter; and this is most manifest in organs of the greatest\nirritability. The coats of the capillaries successively becoming\nthinner and thinner, at length disappear altogether, and the vessels\nultimately terminate in membraneless canals formed in the substance of\nthe tissues. \"The blood in the finest capillaries,\" says Wedemeyer,\n\"no longer flows within actual vessels; it is not contained in tubes\nwhose parietes are formed by a membranous substance distinguishable by\nits texture and compactness from the adjoining cellular tissue: it is\ncontained in the different tissues in channels which it forms in them\nfor itself; and, under the microscope, the stream is seen easily and\nrapidly to work out for itself a new passage in the tissues which it\npenetrates.\"\n\n305. Some of these fine capillaries, before they entirely lose their\nmembranous tunics, communicate directly with veins. Of the capillaries\nwhich terminate by direct communication with veins, some are large\nenough to admit of three or four of the red particles of the blood\nabreast; the diameter of others is sufficient to admit only of one;\nwhile others are so small that they can transmit nothing but the serum\nof the blood. As long as the capillary is of sufficient magnitude\nto receive three or four of the particles abreast, it is evident\nthat it possesses regular parietes; but by far the greater number,\nbefore they communicate with veins, lose altogether their membranous\ncoats. There are no visible openings or pores in the sides or ends\nof the capillaries by means of which the blood can be extravasated,\npreparatory to its being imbibed by the veins. There is nowhere\napparent a sudden passage of the arterial into the venous stream; no\nabrupt boundary between the division of the two systems. The arterial\nstreamlet winds through long routes, and describes numerous turns\nbefore it assumes the nature and takes the direction of a venous\nstreamlet. The ultimate capillary rarely passes from a large arterial\ninto a large venous branch.\n\n306. The vital power which it has been shown (298) is possessed by\nthe arterial trunks and branches, is still more intense in the minute\ncapillaries. If alcohol, strong acetic acid, naphtha, and other\nstimulating fluids, be injected into the arteries of a living animal,\nit is found that they are not transmitted through the capillaries\nat all, or, at all events, that they make their way through them\nwith extreme difficulty; whereas mild, unirritating fluids pass with\nrapidity and ease. Wedemeyer exposed and divided the main artery in\nthe fore-leg of a horse, together with the corresponding vein in the\nshoulder. Several syringes-full of tepid water were now injected into\nthe lower end of the artery. The gentlest pressure was sufficient to\nforce the fluid through the capillaries. At each injection the water\nissued in a full stream from the aperture of the vein, the flow of the\nfluid ceasing as soon as the injection was stopped. Next, instead of\nwater, four syringes-full of pure cold brandy were injected. To propel\nthis fluid through the capillaries, so as to render its smell and taste\nperceptible at the aperture of the vein, required a great degree of\npressure; and when at last the fluid issued from the vein, it merely\ntrickled in a feeble stream.\n\nThe experiment being repeated on another horse with vinegar, six\nsyringes-full of which being injected in rapid succession, at first\nthis fluid passed as easily as water, afterwards it flowed with greater\ndifficulty and in a small stream; before long the force required to\npropel it was extreme, and at last the obstruction to its passage\nbecame complete, so that no fluid whatever issued from the vein.\n\nThese experiments, whenever repeated, afforded the same result, and\nthey demonstrate that the capillaries are capable of being stimulated\nto contract upon their contents, and that they can contract with such\nforce as to stop the current. It is manifest that the power by which\nthey do this is vital, because after death all fluids, the mildest and\nthe most acrid, pass through them with equal facility.\n\n307. Drs. Thompson, Philip, Hastings, and others in this country,\nhave applied stimulants of various kinds to the capillary arteries,\nin order to observe with the microscope the changes which the vessels\nundergo. The results of these experiments, performed independently,\nagree with each other; and all the observers concur in stating that\nthose results are so obvious and decisive as to admit of no question.\nWedemeyer, fully aware of all that had been done on this subject by\nthe English physiologists, repeated their experiments with his usual\npatience and care, vigilantly watching the effects with his microscope.\nHis observations completely coincide with those of our countrymen. The\ncirculation being observed in the mesentery of the frog and in the web\nof its foot, it was apparent that no change whatever took place in\nthe diameter of the small arteries, nor in that of the capillaries,\nas long as the circulation was allowed to go on in its natural state;\nbut as soon as stimulants were applied to them, an alteration of their\ndiameter was visible. Alcohol, without much apparent contraction of the\nvessels, stopped the flow of the blood. Muriate of soda, in the course\nof three or four minutes, caused the vessels to contract one-fifth of\ntheir calibre, which contraction was followed by dilatation and gradual\nretardation and stoppage of the blood. Ammonia caused immediate and\ndirect dilatation, and the effect of galvanism was still more striking.\nIn a space of time varying from ten to thirty seconds, nay, sometimes\nimmediately after the completion of the galvanic circle, the vessels\ncontracted, some a fourth, others half, and others three-fourths, of\ntheir calibre. The flow of the blood through the contracted vessels\nwas accelerated. The contraction sometimes lasted a considerable time,\noccasionally several hours; in other instances the contraction ceased\nin ten minutes, and the vessels resumed their natural diameter. A\nsecond application of galvanism to the same capillaries seldom caused\nany material contraction.\n\n308. The evidence, then, is abundant that stimulants are capable of\nmodifying to a great extent the action of the capillary arteries,\nsometimes causing them to contract, at other times to dilate; sometimes\nquickening the flow of blood through them, at other times retarding it,\nand frequently altogether arresting its motion. This contractile power\nof the capillaries must be a vital endowment, for no such property is\npossessed by any substance destitute of life, and there is satisfactory\nevidence that it is communicated, regulated, and controlled by the\norganic nerves, which, as has been shown, increase as the size of the\nvessels and the thickness of their membranous tunics diminish. The\npowerful influence of these nerves upon the capillary vessels is placed\nbeyond doubt or controversy by the obvious local changes produced in\nthe capillary circulation by sudden, and even by mental, impressions,\nby the flush of the cheek and the sparkle of the eye, at a thought\nconceived or a sound heard; changes which can be effected, as far as we\nhave any knowledge, by no medium excepting that of the nerves. The part\nperformed by electricity, the physical agent by which it is conceived\nthe nerves operate, will be considered hereafter.\n\n309. Exerting upon each other a vital force of repulsion, under a\nvital influence derived from the organic nerves, urged by the vital\ncontraction of the heart, the particles of the blood reach the extreme\ncapillaries. Most of these capillaries terminate (304) in canals, which\nthey work out for themselves in the substance of the tissues. The\ntissues are endowed with a vital attractive force, which they exert\nupon the blood\u2014an elective as well as an attractive force: for in\nevery part of the body, in the brain, the heart, the lung, the muscle,\nthe membrane, the bone, each tissue attracts only those constituents\nof which it is itself composed. Thus the common current, rich in all\nthe proximate constituents of the tissues, flows out to each. As the\ncurrent approaches the tissue, the particles appropriate to the tissue\nfeel its attractive force, obey it, quit the stream, mingle with the\nsubstance of the tissue, become identified with it, and are changed\ninto its own true and proper nature. Meantime, the particles which are\nnot appropriate to that particular tissue, not being attracted by it,\ndo not quit the current, but passing on, are borne by other capillaries\nto other tissues, to which they are appropriate, and by which they\nare apprehended and assimilated, When it has given to the tissues the\nconstituents with which it abounded, and received from them particles\nno longer useful, and which would become noxious, the blood flows into\nthe veins to be returned by the pulmonic heart to the lung, where,\nparting with the useless and noxious matter it has accumulated, and,\nreplenished with new proximate principles, it returns to the systemic\nheart, by which it is again sent back to the tissues.\n\n310. Particles of blood are seen to quit the current and mingle with\nthe tissues; particles are seen to quit the tissues and mingle with\nthe current. But all that we can see, with the best aid we can get,\ndoes but bring us to the confines of the grand operations that go on,\nof which we are altogether ignorant. Arterial blood is conveyed by\nthe arteries to the capillaries; but before it has passed from under\nthe influence of the capillaries it has ceased to be arterial blood.\nArterial blood is conveyed by the carotid artery to the brain; but\nthe cerebral capillaries do not deposit blood, but brain. Arterial\nblood is conveyed by its nutrient arteries to bone, but the osseous\ncapillaries do not deposit blood, but bone. Arterial blood is conveyed\nby the muscular arteries to muscle, but the muscular capillaries do not\ndeposit blood, but muscle. The blood conveyed by the capillaries of\nbrain, bone, and muscle is the same, all comes alike from the systemic\nheart, and is alike conveyed to all tissues; yet in the one it becomes\nbrain, in the other bone, and in the third muscle. Out of one and the\nsame fluid these living chemists manufacture cuticle, and membrane, and\nmuscle, and brain, and bone; the tears, the wax, the fat, the saliva,\nthe gastric juice, the milk, the bile, all the fluids, and all the\nsolids of the body.\n\n311. And they do still more; for they are architects as well as\nchemists; after they have manufactured the tissue, they construct the\norgan. The capillaries of the eye not only form its different membranes\nand humours, but arrange them in such a manner as to constitute the\noptical instrument; and the capillaries of the brain not only form\ncerebral matter, but build it up into the instrument of sensation,\nthought, and motion.\n\n312. The practical applications of these phenomena are numerous and\nmost important; but they can be clearly and impressively stated\nonly when the operation of the physical agents which influence the\ncirculation, and which proportionally affect life and health, has been\nexplained.\n\n\n\n\nFOOTNOTES.\n\n\n[1] Computationi in alimentis faciend\u00e6 hanc formam esse Ulpianus\nscribit, ut _\u00e0 prim\u00e2 \u00e6tate_ usque ad annum vicesimum quantitas\nalimentorum triginta annorum computetur, ejusque quantitatis Falcidia\npr\u00e6stetur: _ab annis ver\u00f2 viginti_ usque ad annum vicesimumquintum\nannorum viginti octo: _ab annis vigintiquinque_ usque ad annos\ntriginta, annorum vigintiquinque: _ab annis triginta_ usque ad annos\ntrigintaquinque annorum viginti duo; _ab annis trigintaquinque_\nusque ad annos quadraginta annorum viginti: _ab annis quadraginta_\nusque ad annos quinquaginta tot annorum computatio fit quot \u00e6tate\nejus ad annum sexagesimum deerit, remisso uno anno: _ab anno ver\u00f2\nquinquagesimo_ usque ad annum quinquagesimumquintum annorum novem:\n_ab annis quinquagintaquinque_ usque ad annum sexagesimum annorum\nseptem: _ab annis sexaginta_, cujuscunque \u00e6tatis sit, annorum quinque;\neoque nos jure uti Ulpianus ait, et circa compu tationem ususfructus\nfaciendam. Solitum est tamen _\u00e0 prim\u00e2 \u00e6tate_ usque ad annum trigesimum\ncomputationem annorum triginta fieri: _ab annis ver\u00f2 triginta_ tot\nannorum computationem inire, quot ad annum sexagesimum deesse videntur;\nnunquam ergo amplius quam triginta aunorum computatio initur. Sic\ndenique, et si Reipublic\u00e6 ususfructus egetur, sive simpliciter, sive\nad ludos, triginta annorum computatio fit. Si quis ex heredibus rem\npropriam esse contendat, deinde hereditariam esse convincatur: quidem\nputant ejus quoque Falcidiam non posse retineri; qui\u00e0 nihil intersit,\nsubtraxerit an hereditariam esse negaverit. Quod Ulpianus rect\u00e8\nimprobat. (Vide Justin. Pandect. lib. 35, tit. 2, ad Legem Falcidiam.)\n\n[2] Which maximum is a little above the highest point hitherto any\nwhere attained.\n\n[3] Hence in the preparation of jelly as an article of diet, the parts\nof young animals, as the feet of the calf, are principally employed;\nwhereas soups made from beef contain a large proportion of albumen,\nwhile in those made from veal the proportion of jelly preponderates.\n\n[4] Treatise on Ligaments, by Bransby B. Cooper, Esq.\n\n[5] For these illustrations I am indebted to Mr. Lister, who has been\nso kind as to make drawings of the objects for me.\n\n[6] Whenever there is any interruption to the ordinary flow of the\ncirculating fluids, the powers of the anastomosing circulation are\ncapable of being increased to a surprising extent. The aorta itself\nhas frequently been tied in animals of considerable size without\ndestroying life; in the human body it has also been found obliterated\nby disease in different parts of its course, in one case as high\nas the termination of its curvature. In the cure for aneurism the\nexternal iliac artery has been tied by Mr. Abernethy with success; the\nsubclavian artery below the clavicle by Mr. Keate; the common carotid\nby Sir Astley Cooper; the subclavian artery above the clavicle by\nMr. Ramsden; the internal iliac artery by Dr. Stevens; the arteria\ninnominata by Dr. Mott, of New York; and lastly, the abdominal aorta\nitself, by Sir A. Cooper. Mr. Grainger tied the abdominal aorta of a\ndog; when the animal had recovered from that operation, the carotids\nand the great trunks of the anterior extremities were tied: in this\nmanner the whole course of the circulation was altered. The dog, which\nwas of very large size, survived all these operations, and appeared to\nenjoy its ordinary health. Grainger's General Anatomy, p. 251-253.\n\n[7] See this matter very ably discussed in Dr. Arnott's excellent work\non the Elements of Physics, vol. i.\n\n\nEND OF VOL. I.\n\n\nLondon: Printed by W. CLOWES and SONS, Stamford Street.\n\n\n\n\nTRANSCRIBER'S NOTES.\n1. (Figure LXXIV.) was incorrectly labeled as (Figure LXXVI.).\n     This has been corrected.\n2. No Figure LXX in original book.","title":"The Philosophy of Health; Volume 1 (of 2): or, an exposition of the physical and mental constitution of man","tradition":"philosophy-ethics","translated_text":null,"word_count":82175}