{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_2923/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_2923","id":"gutenberg_2923","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/2923","summary":null,"tags":["Category: History - Modern (1750+)","Category: Philosophy & Ethics","Category: Science - Biology","Darwin, Charles, 1809-1882. On the origin of species","Evolution (Biology)"],"text":"Produced by Amy E. Zelmer\n\n\n\n\n\nTHE METHOD BY WHICH THE CAUSES OF THE PRESENT AND PAST CONDITIONS OF\nORGANIC NATURE ARE TO BE DISCOVERED.--THE ORIGINATION OF LIVING BEINGS\n\nLecture III. (of VI.), Lectures To Working Men, at the Museum of\nPractical Geology, 1863, On Darwin's work: \"Origin of Species\".\n\n\nBy Thomas H. Huxley\n\n\n\nIn the two preceding lectures I have endeavoured to indicate to you the\nextent of the subject-matter of the inquiry upon which we are engaged;\nand now, having thus acquired some conception of the Past and Present\nphenomena of Organic Nature, I must now turn to that which constitutes\nthe great problem which we have set before ourselves;--I mean, the\nquestion of what knowledge we have of the causes of these phenomena of\norganic nature, and how such knowledge is obtainable.\n\nHere, on the threshold of the inquiry, an objection meets us. There are\nin the world a number of extremely worthy, well-meaning persons, whose\njudgments and opinions are entitled to the utmost respect on account of\ntheir sincerity, who are of opinion that Vital Phenomena, and especially\nall questions relating to the origin of vital phenomena, are questions\nquite apart from the ordinary run of inquiry, and are, by their very\nnature, placed out of our reach. They say that all these phenomena\noriginated miraculously, or in some way totally different from the\nordinary course of nature, and that therefore they conceive it to be\nfutile, not to say presumptuous, to attempt to inquire into them.\n\nTo such sincere and earnest persons, I would only say, that a question\nof this kind is not to be shelved upon theoretical or speculative\ngrounds. You may remember the story of the Sophist who demonstrated to\nDiogenes in the most complete and satisfactory manner that he could not\nwalk; that, in fact, all motion was an impossibility; and that Diogenes\nrefuted him by simply getting up and walking round his tub. So, in the\nsame way, the man of science replies to objections of this kind, by\nsimply getting up and walking onward, and showing what science has done\nand is doing--by pointing to that immense mass of facts which have been\nascertained and systematized under the forms of the great doctrines of\nMorphology, of Development, of Distribution, and the like. He sees an\nenormous mass of facts and laws relating to organic beings, which\nstand on the same good sound foundation as every other natural law; and\ntherefore, with this mass of facts and laws before us, therefore,\nseeing that, as far as organic matters have hitherto been accessible and\nstudied, they have shown themselves capable of yielding to scientific\ninvestigation, we may accept this as proof that order and law reign\nthere as well as in the rest of nature; and the man of science says\nnothing to objectors of this sort, but supposes that we can and shall\nwalk to a knowledge of the origin of organic nature, in the same way\nthat we have walked to a knowledge of the laws and principles of the\ninorganic world.\n\nBut there are objectors who say the same from ignorance and ill-will. To\nsuch I would reply that the objection comes ill from them, and that the\nreal presumption, I may almost say the real blasphemy, in this matter,\nis in the attempt to limit that inquiry into the causes of phenomena\nwhich is the source of all human blessings, and from which has sprung\nall human prosperity and progress; for, after all, we can accomplish\ncomparatively little; the limited range of our own faculties bounds us\non every side,--the field of our powers of observation is small enough,\nand he who endeavours to narrow the sphere of our inquiries is only\npursuing a course that is likely to produce the greatest harm to his\nfellow-men.\n\nBut now, assuming, as we all do, I hope, that these phenomena are\nproperly accessible to inquiry, and setting out upon our search into the\ncauses of the phenomena of organic nature, or, at any rate, setting out\nto discover how much we at present know upon these abstruse matters, the\nquestion arises as to what is to be our course of proceeding, and what\nmethod we must lay down for our guidance. I reply to that question,\nthat our method must be exactly the same as that which is pursued in any\nother scientific inquiry, the method of scientific investigation being\nthe same for all orders of facts and phenomena whatsoever.\n\nI must dwell a little on this point, for I wish you to leave this room\nwith a very clear conviction that scientific investigation is not, as\nmany people seem to suppose, some kind of modern black art. I say that\nyou might easily gather this impression from the manner in which\nmany persons speak of scientific inquiry, or talk about inductive and\ndeductive philosophy, or the principles of the \"Baconian philosophy.\"\nI do protest that, of the vast number of cants in this world, there are\nnone, to my mind, so contemptible as the pseudoscientific cant which is\ntalked about the \"Baconian philosophy.\"\n\nTo hear people talk about the great Chancellor--and a very great man he\ncertainly was,--you would think that it was he who had invented science,\nand that there was no such thing as sound reasoning before the time of\nQueen Elizabeth. Of course you say, that cannot possibly be true; you\nperceive, on a moment's reflection, that such an idea is absurdly wrong,\nand yet, so firmly rooted is this sort of impression,--I cannot call it\nan idea, or conception,--the thing is too absurd to be entertained,--but\nso completely does it exist at the bottom of most men's minds, that this\nhas been a matter of observation with me for many years past. There\nare many men who, though knowing absolutely nothing of the subject with\nwhich they may be dealing, wish, nevertheless, to damage the author of\nsome view with which they think fit to disagree. What they do, then,\nis not to go and learn something about the subject, which one would\nnaturally think the best way of fairly dealing with it; but they abuse\nthe originator of the view they question, in a general manner, and wind\nup by saying that, \"After all, you know, the principles and method\nof this author are totally opposed to the canons of the Baconian\nphilosophy.\" Then everybody applauds, as a matter of course, and agrees\nthat it must be so. But if you were to stop them all in the middle of\ntheir applause, you would probably find that neither the speaker nor his\napplauders could tell you how or in what way it was so; neither the\none nor the other having the slightest idea of what they mean when they\nspeak of the \"Baconian philosophy.\"\n\nYou will understand, I hope, that I have not the slightest desire to\njoin in the outcry against either the morals, the intellect, or the\ngreat genius of Lord Chancellor Bacon. He was undoubtedly a very great\nman, let people say what they will of him; but notwithstanding all that\nhe did for philosophy, it would be entirely wrong to suppose that the\nmethods of modern scientific inquiry originated with him, or with his\nage; they originated with the first man, whoever he was; and indeed\nexisted long before him, for many of the essential processes of\nreasoning are exerted by the higher order of brutes as completely and\neffectively as by ourselves. We see in many of the brute creation the\nexercise of one, at least, of the same powers of reasoning as that which\nwe ourselves employ.\n\nThe method of scientific investigation is nothing but the expression of\nthe necessary mode of working of the human mind. It is simply the mode\nat which all phenomena are reasoned about, rendered precise and\nexact. There is no more difference, but there is just the same kind of\ndifference, between the mental operations of a man of science and those\nof an ordinary person, as there is between the operations and methods of\na baker or of a butcher weighing out his goods in common scales, and the\noperations of a chemist in performing a difficult and complex analysis\nby means of his balance and finely-graduated weights. It is not that\nthe action of the scales in the one case, and the balance in the other,\ndiffer in the principles of their construction or manner of working; but\nthe beam of one is set on an infinitely finer axis than the other, and\nof course turns by the addition of a much smaller weight.\n\nYou will understand this better, perhaps, if I give you some familiar\nexample. You have all heard it repeated, I dare say, that men of science\nwork by means of Induction and Deduction, and that by the help of these\noperations, they, in a sort of sense, wring from Nature certain other\nthings, which are called Natural Laws, and Causes, and that out of\nthese, by some cunning skill of their own, they build up Hypotheses and\nTheories. And it is imagined by many, that the operations of the common\nmind can be by no means compared with these processes, and that they\nhave to be acquired by a sort of special apprenticeship to the craft.\nTo hear all these large words, you would think that the mind of a man of\nscience must be constituted differently from that of his fellow men; but\nif you will not be frightened by terms, you will discover that you are\nquite wrong, and that all these terrible apparatus are being used by\nyourselves every day and every hour of your lives.\n\nThere is a well-known incident in one of Moliere's plays, where the\nauthor makes the hero express unbounded delight on being told that he\nhad been talking prose during the whole of his life. In the same way, I\ntrust, that you will take comfort, and be delighted with yourselves, on\nthe discovery that you have been acting on the principles of inductive\nand deductive philosophy during the same period. Probably there is not\none here who has not in the course of the day had occasion to set in\nmotion a complex train of reasoning, of the very same kind, though\ndiffering of course in degree, as that which a scientific man goes\nthrough in tracing the causes of natural phenomena.\n\nA very trivial circumstance will serve to exemplify this. Suppose you\ngo into a fruiterer's shop, wanting an apple,--you take up one, and, on\nbiting it, you find it is sour; you look at it, and see that it is hard\nand green. You take up another one, and that too is hard, green, and\nsour. The shopman offers you a third; but, before biting it, you examine\nit, and find that it is hard and green, and you immediately say that you\nwill not have it, as it must be sour, like those that you have already\ntried.\n\nNothing can be more simple than that, you think; but if you will take\nthe trouble to analyze and trace out into its logical elements what\nhas been done by the mind, you will be greatly surprised. In the first\nplace, you have performed the operation of Induction. You found that,\nin two experiences, hardness and greenness in apples go together with\nsourness. It was so in the first case, and it was confirmed by the\nsecond. True, it is a very small basis, but still it is enough to make\nan induction from; you generalize the facts, and you expect to find\nsourness in apples where you get hardness and greenness. You found upon\nthat a general law, that all hard and green apples are sour; and that,\nso far as it goes, is a perfect induction. Well, having got your natural\nlaw in this way, when you are offered another apple which you find is\nhard and green, you say, \"All hard and green apples are sour; this\napple is hard and green, therefore this apple is sour.\" That train of\nreasoning is what logicians call a syllogism, and has all its various\nparts and terms,--its major premiss, its minor premiss, and its\nconclusion. And, by the help of further reasoning, which, if drawn out,\nwould have to be exhibited in two or three other syllogisms, you arrive\nat your final determination, \"I will not have that apple.\" So that, you\nsee, you have, in the first place, established a law by Induction, and\nupon that you have founded a Deduction, and reasoned out the special\nconclusion of the particular case. Well now, suppose, having got your\nlaw, that at some time afterwards, you are discussing the qualities\nof apples with a friend: you will say to him, \"It is a very curious\nthing,--but I find that all hard and green apples are sour!\" Your friend\nsays to you, \"But how do you know that?\" You at once reply, \"Oh, because\nI have tried it over and over again, and have always found them to be\nso.\" Well, if we were talking science instead of common sense, we should\ncall that an Experimental Verification. And, if still opposed, you go\nfurther, and say, \"I have heard from the people in Somersetshire and\nDevonshire, where a large number of apples are grown, that they have\nobserved the same thing. It is also found to be the case in Normandy,\nand in North America. In short, I find it to be the universal experience\nof mankind wherever attention has been directed to the subject.\"\nWhereupon, your friend, unless he is a very unreasonable man, agrees\nwith you, and is convinced that you are quite right in the conclusion\nyou have drawn. He believes, although perhaps he does not know he\nbelieves it, that the more extensive Verifications are,--that the more\nfrequently experiments have been made, and results of the same kind\narrived at,--that the more varied the conditions under which the same\nresults have been attained, the more certain is the ultimate conclusion,\nand he disputes the question no further. He sees that the experiment has\nbeen tried under all sorts of conditions, as to time, place, and people,\nwith the same result; and he says with you, therefore, that the law you\nhave laid down must be a good one, and he must believe it.\n\nIn science we do the same thing;--the philosopher exercises precisely\nthe same faculties, though in a much more delicate manner. In scientific\ninquiry it becomes a matter of duty to expose a supposed law to every\npossible kind of verification, and to take care, moreover, that this is\ndone intentionally, and not left to a mere accident, as in the case of\nthe apples. And in science, as in common life, our confidence in a law\nis in exact proportion to the absence of variation in the result of our\nexperimental verifications. For instance, if you let go your grasp of\nan article you may have in your hand, it will immediately fall to\nthe ground. That is a very common verification of one of the best\nestablished laws of nature--that of gravitation. The method by which men\nof science establish the existence of that law is exactly the same as\nthat by which we have established the trivial proposition about\nthe sourness of hard and green apples. But we believe it in such an\nextensive, thorough, and unhesitating manner because the universal\nexperience of mankind verifies it, and we can verify it ourselves at any\ntime; and that is the strongest possible foundation on which any natural\nlaw can rest.\n\nSo much by way of proof that the method of establishing laws in science\nis exactly the same as that pursued in common life. Let us now turn\nto another matter (though really it is but another phase of the same\nquestion), and that is, the method by which, from the relations of\ncertain phenomena, we prove that some stand in the position of causes\ntowards the others.\n\nI want to put the case clearly before you, and I will therefore show you\nwhat I mean by another familiar example. I will suppose that one of you,\non coming down in the morning to the parlour of your house, finds that a\ntea-pot and some spoons which had been left in the room on the previous\nevening are gone,--the window is open, and you observe the mark of a\ndirty hand on the window-frame, and perhaps, in addition to that, you\nnotice the impress of a hob-nailed shoe on the gravel outside. All these\nphenomena have struck your attention instantly, and before two minutes\nhave passed you say, \"Oh, somebody has broken open the window, entered\nthe room, and run off with the spoons and the tea-pot!\" That speech is\nout of your mouth in a moment. And you will probably add, \"I know there\nhas; I am quite sure of it!\" You mean to say exactly what you know; but\nin reality what you have said has been the expression of what is, in all\nessential particulars, an Hypothesis. You do not 'know' it at all; it is\nnothing but an hypothesis rapidly framed in your own mind! And it is an\nhypothesis founded on a long train of inductions and deductions.\n\nWhat are those inductions and deductions, and how have you got at this\nhypothesis? You have observed, in the first place, that the window\nis open; but by a train of reasoning involving many Inductions and\nDeductions, you have probably arrived long before at the General\nLaw--and a very good one it is--that windows do not open of themselves;\nand you therefore conclude that something has opened the window. A\nsecond general law that you have arrived at in the same way is, that\ntea-pots and spoons do not go out of a window spontaneously, and you are\nsatisfied that, as they are not now where you left them, they have been\nremoved. In the third place, you look at the marks on the window-sill,\nand the shoemarks outside, and you say that in all previous experience\nthe former kind of mark has never been produced by anything else but\nthe hand of a human being; and the same experience shows that no other\nanimal but man at present wears shoes with hob-nails on them such as\nwould produce the marks in the gravel. I do not know, even if we could\ndiscover any of those \"missing links\" that are talked about, that they\nwould help us to any other conclusion! At any rate the law which states\nour present experience is strong enough for my present purpose.--You\nnext reach the conclusion, that as these kinds of marks have not been\nleft by any other animals than men, or are liable to be formed in any\nother way than by a man's hand and shoe, the marks in question have been\nformed by a man in that way. You have, further, a general law, founded\non observation and experience, and that, too, is, I am sorry to say, a\nvery universal and unimpeachable one,--that some men are thieves;\nand you assume at once from all these premisses--and that is what\nconstitutes your hypothesis--that the man who made the marks outside and\non the window-sill, opened the window, got into the room, and stole your\ntea-pot and spoons. You have now arrived at a 'Vera Causa';--you have\nassumed a Cause which it is plain is competent to produce all the\nphenomena you have observed. You can explain all these phenomena only by\nthe hypothesis of a thief. But that is a hypothetical conclusion, of the\njustice of which you have no absolute proof at all; it is only rendered\nhighly probable by a series of inductive and deductive reasonings.\n\nI suppose your first action, assuming that you are a man of ordinary\ncommon sense, and that you have established this hypothesis to your own\nsatisfaction, will very likely be to go off for the police, and set\nthem on the track of the burglar, with the view to the recovery of your\nproperty. But just as you are starting with this object, some person\ncomes in, and on learning what you are about, says, \"My good friend,\nyou are going on a great deal too fast. How do you know that the man who\nreally made the marks took the spoons? It might have been a monkey that\ntook them, and the man may have merely looked in afterwards.\" You would\nprobably reply, \"Well, that is all very well, but you see it is contrary\nto all experience of the way tea-pots and spoons are abstracted; so\nthat, at any rate, your hypothesis is less probable than mine.\" While\nyou are talking the thing over in this way, another friend arrives, one\nof that good kind of people that I was talking of a little while ago.\nAnd he might say, \"Oh, my dear sir, you are certainly going on a great\ndeal too fast. You are most presumptuous. You admit that all these\noccurrences took place when you were fast asleep, at a time when you\ncould not possibly have known anything about what was taking place. How\ndo you know that the laws of Nature are not suspended during the night?\nIt may be that there has been some kind of supernatural interference in\nthis case.\" In point of fact, he declares that your hypothesis is one\nof which you cannot at all demonstrate the truth, and that you are by no\nmeans sure that the laws of Nature are the same when you are asleep as\nwhen you are awake.\n\nWell, now, you cannot at the moment answer that kind of reasoning. You\nfeel that your worthy friend has you somewhat at a disadvantage. You\nwill feel perfectly convinced in your own mind, however, that you are\nquite right, and you say to him, \"My good friend, I can only be guided\nby the natural probabilities of the case, and if you will be kind enough\nto stand aside and permit me to pass, I will go and fetch the police.\"\nWell, we will suppose that your journey is successful, and that by good\nluck you meet with a policeman; that eventually the burglar is found\nwith your property on his person, and the marks correspond to his hand\nand to his boots. Probably any jury would consider those facts a very\ngood experimental verification of your hypothesis, touching the cause\nof the abnormal phenomena observed in your parlour, and would act\naccordingly.\n\nNow, in this suppositious case, I have taken phenomena of a very common\nkind, in order that you might see what are the different steps in an\nordinary process of reasoning, if you will only take the trouble to\nanalyse it carefully. All the operations I have described, you will\nsee, are involved in the mind of any man of sense in leading him to\na conclusion as to the course he should take in order to make good a\nrobbery and punish the offender. I say that you are led, in that case,\nto your conclusion by exactly the same train of reasoning as that which\na man of science pursues when he is endeavouring to discover the origin\nand laws of the most occult phenomena. The process is, and always must\nbe, the same; and precisely the same mode of reasoning was employed by\nNewton and Laplace in their endeavours to discover and define the causes\nof the movements of the heavenly bodies, as you, with your own common\nsense, would employ to detect a burglar. The only difference is, that\nthe nature of the inquiry being more abstruse, every step has to be most\ncarefully watched, so that there may not be a single crack or flaw in\nyour hypothesis. A flaw or crack in many of the hypotheses of daily life\nmay be of little or no moment as affecting the general correctness of\nthe conclusions at which we may arrive; but, in a scientific inquiry,\na fallacy, great or small, is always of importance, and is sure to be\nconstantly productive of mischievous, if not fatal results.\n\nDo not allow yourselves to be misled by the common notion that an\nhypothesis is untrustworthy simply because it is an hypothesis. It is\noften urged, in respect to some scientific conclusion, that, after\nall, it is only an hypothesis. But what more have we to guide us in\nnine-tenths of the most important affairs of daily life than hypotheses,\nand often very ill-based ones? So that in science, where the evidence of\nan hypothesis is subjected to the most rigid examination, we may rightly\npursue the same course. You may have hypotheses and hypotheses. A man\nmay say, if he likes, that the moon is made of green cheese: that is an\nhypothesis. But another man, who has devoted a great deal of time and\nattention to the subject, and availed himself of the most powerful\ntelescopes and the results of the observations of others, declares that\nin his opinion it is probably composed of materials very similar to\nthose of which our own earth is made up: and that is also only an\nhypothesis. But I need not tell you that there is an enormous difference\nin the value of the two hypotheses. That one which is based on sound\nscientific knowledge is sure to have a corresponding value; and that\nwhich is a mere hasty random guess is likely to have but little value.\nEvery great step in our progress in discovering causes has been made\nin exactly the same way as that which I have detailed to you. A person\nobserving the occurrence of certain facts and phenomena asks, naturally\nenough, what process, what kind of operation known to occur in nature\napplied to the particular case, will unravel and explain the mystery?\nHence you have the scientific hypothesis; and its value will be\nproportionate to the care and completeness with which its basis had been\ntested and verified. It is in these matters as in the commonest affairs\nof practical life: the guess of the fool will be folly, while the guess\nof the wise man will contain wisdom. In all cases, you see that the\nvalue of the result depends on the patience and faithfulness with\nwhich the investigator applies to his hypothesis every possible kind of\nverification.\n\nI dare say I may have to return to this point by-and-by; but having\ndealt thus far with our logical methods, I must now turn to something\nwhich, perhaps, you may consider more interesting, or, at any rate,\nmore tangible. But in reality there are but few things that can be more\nimportant for you to understand than the mental processes and the means\nby which we obtain scientific conclusions and theories. [1] Having\ngranted that the inquiry is a proper one, and having determined on\nthe nature of the methods we are to pursue and which only can lead to\nsuccess, I must now turn to the consideration of our knowledge of the\nnature of the processes which have resulted in the present condition of\norganic nature.\n\nHere, let me say at once, lest some of you misunderstand me, that I have\nextremely little to report. The question of how the present condition of\norganic nature came about, resolves itself into two questions. The first\nis: How has organic or living matter commenced its existence? And the\nsecond is: How has it been perpetuated? On the second question I shall\nhave more to say hereafter. But on the first one, what I now have to say\nwill be for the most part of a negative character.\n\nIf you consider what kind of evidence we can have upon this matter, it\nwill resolve itself into two kinds. We may have historical evidence and\nwe may have experimental evidence. It is, for example, conceivable, that\ninasmuch as the hardened mud which forms a considerable portion of the\nthickness of the earth's crust contains faithful records of the past\nforms of life, and inasmuch as these differ more and more as we go\nfurther down,--it is possible and conceivable that we might come to\nsome particular bed or stratum which should contain the remains of those\ncreatures with which organic life began upon the earth. And if we did\nso, and if such forms of organic life were preservable, we should have\nwhat I would call historical evidence of the mode in which organic life\nbegan upon this planet. Many persons will tell you, and indeed you will\nfind it stated in many works on geology, that this has been done, and\nthat we really possess such a record; there are some who imagine that\nthe earliest forms of life of which we have as yet discovered any\nrecord, are in truth the forms in which animal life began upon the\nglobe. The grounds on which they base that supposition are these:--That\nif you go through the enormous thickness of the earth's crust and get\ndown to the older rocks, the higher vertebrate animals--the quadrupeds,\nbirds, and fishes--cease to be found; beneath them you find only the\ninvertebrate animals; and in the deepest and lowest rocks those remains\nbecome scantier and scantier, not in any very gradual progression,\nhowever, until, at length, in what are supposed to be the oldest rocks,\nthe animal remains which are found are almost always confined to four\nforms--'Oldhamia', whose precise nature is not known, whether plant or\nanimal; 'Lingula', a kind of mollusc; 'Trilobites', a crustacean animal,\nhaving the same essential plan of construction, though differing in\nmany details from a lobster or crab; and Hymenocaris, which is also a\ncrustacean. So that you have all the 'Fauna' reduced, at this period,\nto four forms: one a kind of animal or plant that we know nothing about,\nand three undoubted animals--two crustaceans and one mollusc.\n\nI think, considering the organization of these mollusca and crustacea,\nand looking at their very complex nature, that it does indeed require a\nvery strong imagination to conceive that these were the first created of\nall living things. And you must take into consideration the fact that\nwe have not the slightest proof that these which we call the oldest beds\nare really so: I repeat, we have not the slightest proof of it. When you\nfind in some places that in an enormous thickness of rocks there are but\nvery scanty traces of life, or absolutely none at all; and that in other\nparts of the world rocks of the very same formation are crowded with the\nrecords of living forms, I think it is impossible to place any reliance\non the supposition, or to feel oneself justified in supposing that these\nare the forms in which life first commenced. I have not time here\nto enter upon the technical grounds upon which I am led to this\nconclusion,--that could hardly be done properly in half a dozen lectures\non that part alone;--I must content myself with saying that I do not at\nall believe that these are the oldest forms of life.\n\nI turn to the experimental side to see what evidence we have there.\nTo enable us to say that we know anything about the experimental\norigination of organization and life, the investigator ought to be able\nto take inorganic matters, such as carbonic acid, ammonia, water, and\nsalines, in any sort of inorganic combination, and be able to build them\nup into Protein matter, and that that Protein matter ought to begin to\nlive in an organic form. That, nobody has done as yet, and I suspect it\nwill be a long while before anybody does do it. But the thing is by no\nmeans so impossible as it looks; for the researches of modern chemistry\nhave shown us--I won't say the road towards it, but, if I may so say,\nthey have shown the finger-post pointing to the road that may lead to\nit.\n\nIt is not many years ago--and you must recollect that Organic Chemistry\nis a young science, not above a couple of generations old,--you must not\nexpect too much of it; it is not many years ago since it was said to be\nperfectly impossible to fabricate any organic compound; that is to say,\nany non-mineral compound which is to be found in an organized being. It\nremained so for a very long period; but it is now a considerable number\nof years since a distinguished foreign chemist contrived to fabricate\nUrea, a substance of a very complex character, which forms one of the\nwaste products of animal structures. And of late years a number of other\ncompounds, such as Butyric Acid, and others, have been added to the\nlist. I need not tell you that chemistry is an enormous distance from\nthe goal I indicate; all I wish to point out to you is, that it is by no\nmeans safe to say that that goal may not be reached one day. It may be\nthat it is impossible for us to produce the conditions requisite to the\norigination of life; but we must speak modestly about the matter, and\nrecollect that Science has put her foot upon the bottom round of the\nladder. Truly he would be a bold man who would venture to predict where\nshe will be fifty years hence.\n\nThere is another inquiry which bears indirectly upon this question,\nand upon which I must say a few words. You are all of you aware of the\nphenomena of what is called spontaneous generation. Our forefathers,\ndown to the seventeenth century, or thereabouts, all imagined, in\nperfectly good faith, that certain vegetable and animal forms gave\nbirth, in the process of their decomposition, to insect life. Thus,\nif you put a piece of meat in the sun, and allowed it to putrefy, they\nconceived that the grubs which soon began to appear were the result\nof the action of a power of spontaneous generation which the meat\ncontained. And they could give you receipts for making various animal\nand vegetable preparations which would produce particular kinds of\nanimals. A very distinguished Italian naturalist, named Redi, took up\nthe question, at a time when everybody believed in it; among others our\nown great Harvey, the discoverer of the circulation of the blood. You\nwill constantly find his name quoted, however, as an opponent of the\ndoctrine of spontaneous generation; but the fact is, and you will see it\nif you will take the trouble to look into his works, Harvey believed\nit as profoundly as any man of his time; but he happened to enunciate a\nvery curious proposition--that every living thing came from an 'egg'; he\ndid not mean to use the word in the sense in which we now employ it, he\nonly meant to say that every living thing originated in a little rounded\nparticle of organized substance; and it is from this circumstance,\nprobably, that the notion of Harvey having opposed the doctrine\noriginated. Then came Redi, and he proceeded to upset the doctrine in a\nvery simple manner. He merely covered the piece of meat with some very\nfine gauze, and then he exposed it to the same conditions. The result\nof this was that no grubs or insects were produced; he proved that the\ngrubs originated from the insects who came and deposited their eggs in\nthe meat, and that they were hatched by the heat of the sun. By\nthis kind of inquiry he thoroughly upset the doctrine of spontaneous\ngeneration, for his time at least.\n\nThen came the discovery and application of the microscope to scientific\ninquiries, which showed to naturalists that besides the organisms which\nthey already knew as living beings and plants, there were an immense\nnumber of minute things which could be obtained apparently almost at\nwill from decaying vegetable and animal forms. Thus, if you took some\nordinary black pepper or some hay, and steeped it in water, you would\nfind in the course of a few days that the water had become impregnated\nwith an immense number of animalcules swimming about in all directions.\nFrom facts of this kind naturalists were led to revive the theory\nof spontaneous generation. They were headed here by an English\nnaturalist,--Needham,--and afterwards in France by the learned Buffon.\nThey said that these things were absolutely begotten in the water of\nthe decaying substances out of which the infusion was made. It did not\nmatter whether you took animal or vegetable matter, you had only to\nsteep it in water and expose it, and you would soon have plenty of\nanimalcules. They made an hypothesis about this which was a very fair\none. They said, this matter of the animal world, or of the higher\nplants, appears to be dead, but in reality it has a sort of dim life\nabout it, which, if it is placed under fair conditions, will cause it\nto break up into the forms of these little animalcules, and they will go\nthrough their lives in the same way as the animal or plant of which they\nonce formed a part.\n\nThe question now became very hotly debated. Spallanzani, an Italian\nnaturalist, took up opposite views to those of Needham and Buffon, and\nby means of certain experiments he showed that it was quite possible to\nstop the process by boiling the water, and closing the vessel in which\nit was contained. \"Oh!\" said his opponents; \"but what do you know you\nmay be doing when you heat the air over the water in this way? You may\nbe destroying some property of the air requisite for the spontaneous\ngeneration of the animalcules.\"\n\nHowever, Spallanzani's views were supposed to be upon the right side,\nand those of the others fell into discredit; although the fact was\nthat Spallanzani had not made good his views. Well, then, the subject\ncontinued to be revived from time to time, and experiments were made by\nseveral persons; but these experiments were not altogether satisfactory.\nIt was found that if you put an infusion in which animalcules would\nappear if it were exposed to the air into a vessel and boiled it, and\nthen sealed up the mouth of the vessel, so that no air, save such as\nhad been heated to 212 degrees, could reach its contents, that then no\nanimalcules would be found; but if you took the same vessel and exposed\nthe infusion to the air, then you would get animalcules. Furthermore, it\nwas found that if you connected the mouth of the vessel with a red-hot\ntube in such a way that the air would have to pass through the tube\nbefore reaching the infusion, that then you would get no animalcules.\nYet another thing was noticed: if you took two flasks containing the\nsame kind of infusion, and left one entirely exposed to the air, and\nin the mouth of the other placed a ball of cotton wool, so that the air\nwould have to filter itself through it before reaching the infusion,\nthat then, although you might have plenty of animalcules in the first\nflask, you would certainly obtain none from the second.\n\nThese experiments, you see, all tended towards one conclusion--that the\ninfusoria were developed from little minute spores or eggs which\nwere constantly floating in the atmosphere, which lose their power of\ngermination if subjected to heat. But one observer now made another\nexperiment which seemed to go entirely the other way, and puzzled\nhim altogether. He took some of this boiled infusion that I have been\nspeaking of, and by the use of a mercurial bath--a kind of trough used\nin laboratories--he deftly inverted a vessel containing the infusion\ninto the mercury, so that the latter reached a little beyond the level\nof the mouth of the 'inverted' vessel. You see that he thus had a\nquantity of the infusion shut off from any possible communication with\nthe outer air by being inverted upon a bed of mercury.\n\nHe then prepared some pure oxygen and nitrogen gases, and passed them\nby means of a tube going from the outside of the vessel, up through the\nmercury into the infusion; so that he thus had it exposed to a perfectly\npure atmosphere of the same constituents as the external air. Of course,\nhe expected he would get no infusorial animalcules at all in that\ninfusion; but, to his great dismay and discomfiture, he found he almost\nalways did get them.\n\nFurthermore, it has been found that experiments made in the manner\ndescribed above answer well with most infusions; but that if you fill\nthe vessel with boiled milk, and then stop the neck with cotton-wool,\nyou 'will' have infusoria. So that you see there were two experiments\nthat brought you to one kind of conclusion, and three to another; which\nwas a most unsatisfactory state of things to arrive at in a scientific\ninquiry.\n\nSome few years after this, the question began to be very hotly discussed\nin France. There was M. Pouchet, a professor at Rouen, a very learned\nman, but certainly not a very rigid experimentalist. He published a\nnumber of experiments of his own, some of which were very ingenious, to\nshow that if you went to work in a proper way, there was a truth in\nthe doctrine of spontaneous generation. Well, it was one of the most\nfortunate things in the world that M. Pouchet took up this question,\nbecause it induced a distinguished French chemist, M. Pasteur, to take\nup the question on the other side; and he has certainly worked it out\nin the most perfect manner. I am glad to say, too, that he has published\nhis researches in time to enable me to give you an account of them. He\nverified all the experiments which I have just mentioned to you--and\nthen finding those extraordinary anomalies, as in the case of the\nmercury bath and the milk, he set himself to work to discover their\nnature. In the case of milk he found it to be a question of temperature.\nMilk in a fresh state is slightly alkaline; and it is a very curious\ncircumstance, but this very slight degree of alkalinity seems to have\nthe effect of preserving the organisms which fall into it from the\nair from being destroyed at a temperature of 212 degrees, which is the\nboiling point. But if you raise the temperature 10 degrees when you boil\nit, the milk behaves like everything else; and if the air with which\nit comes in contact, after being boiled at this temperature, is passed\nthrough a red-hot tube, you will not get a trace of organisms.\n\nHe then turned his attention to the mercury bath, and found on\nexamination that the surface of the mercury was almost always covered\nwith a very fine dust. He found that even the mercury itself was\npositively full of organic matters; that from being constantly exposed\nto the air, it had collected an immense number of these infusorial\norganisms from the air. Well, under these circumstances he felt that the\ncase was quite clear, and that the mercury was not what it had appeared\nto M. Schwann to be,--a bar to the admission of these organisms; but\nthat, in reality, it acted as a reservoir from which the infusion was\nimmediately supplied with the large quantity that had so puzzled him.\n\nBut not content with explaining the experiments of others, M. Pasteur\nwent to work to satisfy himself completely. He said to himself: \"If\nmy view is right, and if, in point of fact, all these appearances of\nspontaneous generation are altogether due to the falling of minute germs\nsuspended in the atmosphere,--why, I ought not only to be able to show\nthe germs, but I ought to be able to catch and sow them, and produce\nthe resulting organisms.\" He, accordingly, constructed a very ingenious\napparatus to enable him to accomplish this trapping of this \"germ dust\"\nin the air. He fixed in the window of his room a glass tube, in the\ncentre of which he had placed a ball of gun-cotton, which, as you all\nknow, is ordinary cotton-wool, which, from having been steeped in strong\nacid, is converted into a substance of great explosive power. It is also\nsoluble in alcohol and ether. One end of the glass tube was, of course,\nopen to the external air; and at the other end of it he placed an\naspirator, a contrivance for causing a current of the external air to\npass through the tube. He kept this apparatus going for four-and-twenty\nhours, and then removed the 'dusted' gun-cotton, and dissolved it in\nalcohol and ether. He then allowed this to stand for a few hours, and\nthe result was, that a very fine dust was gradually deposited at\nthe bottom of it. That dust, on being transferred to the stage of a\nmicroscope, was found to contain an enormous number of starch grains.\nYou know that the materials of our food and the greater portion of\nplants are composed of starch, and we are constantly making use of it in\na variety of ways, so that there is always a quantity of it suspended\nin the air. It is these starch grains which form many of those bright\nspecks that we see dancing in a ray of light sometimes. But besides\nthese, M. Pasteur found also an immense number of other organic\nsubstances such as spores of fungi, which had been floating about in the\nair and had got caged in this way.\n\nHe went farther, and said to himself, \"If these really are the things\nthat give rise to the appearance of spontaneous generation, I ought to\nbe able to take a ball of this 'dusted' gun-cotton and put it into one\nof my vessels, containing that boiled infusion which has been kept away\nfrom the air, and in which no infusoria are at present developed, and\nthen, if I am right, the introduction of this gun-cotton will give rise\nto organisms.\"\n\nAccordingly, he took one of these vessels of infusion, which had been\nkept eighteen months, without the least appearance of life, and by a\nmost ingenious contrivance, he managed to break it open and introduce\nsuch a ball of gun-cotton, without allowing the infusion or the cotton\nball to come into contact with any air but that which had been subjected\nto a red heat, and in twenty-four hours he had the satisfaction of\nfinding all the indications of what had been hitherto called spontaneous\ngeneration. He had succeeded in catching the germs and developing\norganisms in the way he had anticipated.\n\nIt now struck him that the truth of his conclusions might be\ndemonstrated without all the apparatus he had employed. To do this, he\ntook some decaying animal or vegetable substance, such as urine, which\nis an extremely decomposable substance, or the juice of yeast, or\nperhaps some other artificial preparation, and filled a vessel having a\nlong tubular neck with it. He then boiled the liquid and bent that\nlong neck into an S shape or zig-zag, leaving it open at the end. The\ninfusion then gave no trace of any appearance of spontaneous generation,\nhowever long it might be left, as all the germs in the air were\ndeposited in the beginning of the bent neck. He then cut the tube close\nto the vessel, and allowed the ordinary air to have free and direct\naccess; and the result of that was the appearance of organisms in it, as\nsoon as the infusion had been allowed to stand long enough to allow\nof the growth of those it received from the air, which was about\nforty-eight hours. The result of M. Pasteur's experiments proved,\ntherefore, in the most conclusive manner, that all the appearances of\nspontaneous generation arose from nothing more than the deposition of\nthe germs of organisms which were constantly floating in the air.\n\nTo this conclusion, however, the objection was made, that if that were\nthe cause, then the air would contain such an enormous number of these\ngerms, that it would be a continual fog. But M. Pasteur replied that\nthey are not there in anything like the number we might suppose, and\nthat an exaggerated view has been held on that subject; he showed that\nthe chances of animal or vegetable life appearing in infusions, depend\nentirely on the conditions under which they are exposed. If they are\nexposed to the ordinary atmosphere around us, why, of course, you may\nhave organisms appearing early. But, on the other hand, if they are\nexposed to air from a great height, or from some very quiet cellar, you\nwill often not find a single trace of life.\n\nSo that M. Pasteur arrived at last at the clear and definite result,\nthat all these appearances are like the case of the worms in the piece\nof meat, which was refuted by Redi, simply germs carried by the air and\ndeposited in the liquids in which they afterwards appear. For my own\npart, I conceive that, with the particulars of M. Pasteur's experiments\nbefore us, we cannot fail to arrive at his conclusions; and that the\ndoctrine of spontaneous generation has received a final 'coup de grace'.\n\nYou, of course, understand that all this in no way interferes with the\n'possibility' of the fabrication of organic matters by the direct method\nto which I have referred, remote as that possibility may be.\n\n\n[Footnote 1: Those who wish to study fully the doctrines of which I have\nendeavoured to give some rough and ready illustrations, must read Mr.\nJohn Stuart Mill's 'System of Logic'.]","title":"The Method by Which the Causes of the Present and Past Conditions of Organic Nature Are to Be Discovered; the Origination of Living Beings: Lecture III. (of VI.), \"Lectures to Working Men\", at the Museum of Practical Geology, 1863, on Darwin's Work: \"Origin of Species\"","tradition":"philosophy-ethics","translated_text":null,"word_count":8345}