entitled to the place which is usually assigned to Bacon as the father of the inductive methods; while, on the other hand, it is maintained that in respect of method he did not make any considerable advance upon his predecessors. In my opinion a just estimate lies between these two ex-grappling with problems of a scientific tremes. Take, for example, the following passages from his writings: We must not accept a general principle from logic only, but must prove its application to each fact, for it is in facts that we must seek general principles, and these must always accord with facts. The reason why men do not sufficiently attend to the facts is their want of experience. Hence those accustomed to physical inquiry are more competent to lay down the principles which have an extensive application; whereas others who have been accustomed to many assumptions without the apposition of reality, easily lay down principles because they take few things into consideration. It is not difficult to distinguish between those who argue from facts, and those who argue from notions. Many similar passages to the same effect might be quoted, and it is evident that the true method of inductive research could not well have its leading principles more clearly enunciated. And to say this much is in itself enough to place Aristotle in the foremost rank among the scientific intellects of the world. But it would be unreasonable to expect that this great herald of scientific method should have been able, with any powers of intellect, to have entirely emancipated himself from the whole system of previous thought; or in the course of a single lifetime to have fully learnt the great lesson of method which has only been taught by the best experience of more than twenty centuries after his death. Accordingly we find that, although he clearly divined the true principles of research, he not unfrequently fell short in his application of those principles to practice. In particular, he had no adequate idea of the importance of verifying each step of a research, or each statement of an exposition; and therefore it is painfully often that his own words just quoted admit of being turned against himself: "It is easy to distinguish between those who argue from facts and those who argue from notions." To give only a single example, he says that if a woman who has scarlet fever looks at herself in a mirror, the mirror will become suffused with a bloody mist, which, if the mirror be new, can only be rubbed off with difficulty. Now, instead of proceeding to verify this old wife's tale, he attempts to explain the alleged fact by a rambling assemblage of absurd "notions." And numerous other instances might be given to the same effect. Nevertheless, upon the whole, or as a general rule, in his thought and language, in his mode of conceiving and kind, in the importance which he assigns to the smallest facts, and in the general cast of reasoning which he employs, Aristotle resembles, much more closely than any other philosopher of like antiquity, a scientific investigator of the present day. Thus, in seeking to form a just estimate of Aristotle's work in natural history, we must be careful on the one hand to avoid" the extravagant praise which has been lav. ished upon him, even by such authorities as Cuvier, De Blainville, Isidore St. Hilaire, etc.; and, on the other hand, we must no less carefully avoid the unfairness of contrasting his working methods with those which have now become habitual. In proceeding to consider the extraor dinary labors of this extraordinary man, in so far as they were concerned with nat ural history, I may begin by enumerating, but without waiting to name, the species of animals with which we know that he was acquainted. From his works on natural history, then, we find that he mentions at least seventy species of mammals, one hundred and fifty of birds, twenty of reptiles, one hundred and sixteen of fish, eighty-four of articulata, and about forty of lower forms making close upon five hun dred species in all. That he was accustomed from his earliest boyhood to the anatomical study of animal forms we may infer from the fact of his father having been a physician of eminence, and an Asclepiad; for, according to Galen, it was the custom of the Asclepiads to constitute dissection part of the education of their children. Therefore, as Aristotle's boyhood was passed upon the seacoast, it is probable that from a very early age his studies were directed to the anatomy and physiology of marine animals. But, of course, it must not be concluded from this that the dissections then practised were comparable with what we understand by dissections at the present time. We find abundant evidence in the writings of Aristotle himself that the only kind of anatomy then studied was anatomy of the grosser kind, or such as might be prosecuted with a carving-knife as distinguished from a scalpel. We generally hear it said that as a naturalist Aristotle was a teleologist, or a believer in the doctrine of design as manifested in living things. Therefore I should like to begin by making it clear how far this statement is true; for, unquestionably, when such an intellect as that of Aristotle is at work upon this important question, it behoves us to consider exactly what it was that he concluded. Now, I do not dispute - indeed it would be quite impossible to do so that Aristotle was a teleologist, in the sense of being in every case antecedently convinced that organic structures are adapted to the performance of definite functions, and that the organism as a whole is adapted to the 'conditions of its existence. Thus, for example, he very clearly says: "As every instrument subserves some particular end, that is to say, some special function, so the whole body must be destined to minister to some plenary sphere of action. Just as the saw is made for sawing-this being its function and not sawing for the saw." He a designing or contriving agency, having the attainment of order and harmony as the final end or aim of all her work. appears, however, clearly to have recog. nized that, so far at least as science is concerned, such personification is, as it were, allegorical; for he expressly says that if he were asked whether nature works out her designs with any such conscious deliberation, or intentional adjustment of means to ends, as is the case with a builder or a shipwright, he would not be able to answer. All, therefore, that the teleology of Aristotle amounted to was this: he found that the hypothesis of purpose was a useful working hypothesis in his biological researches. There is nothing to show that he would have followed the natural theologians of modern times, who seek to rear upon this working hypothesis a constructive argument in favor of design. On the other hand, it is certain that he would have differed from these theologians in one important particular. For he But in any other sense than this of rec- everywhere regards the purposes of nature ognizing adaptation in nature, I do not as operating under limitations imposed by think there is evidence of Aristotle having what he calls absolute necessity. Monbeen a teleologist. In his " Metaphysics sters, for example, he says are not the he asks the question whether the principle intentional work of nature herself, but of order and excellence in nature is a self-instances of the victory of matter over existing principle inherent from all eternity nature; that is to say, they are instances in nature herself; or whether it is like the where nature has failed to satisfy those discipline of an army, apparently inherent, conditions of necessity under which she but really due to a general in the back-acts. Thus, even if there be a disposing ground. Aristotle, I say, asks this ques- mind which is the author of nature, action; but he gives no answer. Similarly, cording to Aristotle it is not the mind of in his "Natural History," he simply takes a creator, but rather that of an architect, the facts of order and adaptation as facts who does the best he can with the mateof observation; and, therefore, in biology rials supplied to him, and under the conI do not think that Aristotle can be justly ditions imposed by necessity. credited with teleology in any other sense than a modern Darwinist can be so cred- Turning now to the actual work which ited. That is to say, he is a believer in Aristotle accomplished in the domain of adaptation, or final end; but leaves in biology, I will first enumerate his more abeyance the question of design, or final important discoveries upon matters of cause. The only respect in which he fact, and then proceed to mention his differs from a modern Darwinist-al-more important achievements in the way though even here the school of Wallace of generalization. and Weismann agree with him is in holding that adaptation must be present in all cases, even where the adaptation is not apparent. In the case of rudimentary organs, he is puzzled to account for structures apparently aimless, and therefore he invents what we may term an imaginary aim by saying that nature has supplied these structures as "tokens," whereby to sustain her unity of plan. This idea was prominently revived in modern pre-Darwinian times; but in the present connection it is enough to observe that here, as elsewhere, Aristotle personifies nature as He correctly viewed the blood as the medium of general nutrition, and knew that for this purpose it moved through the blood-vessels from the heart to all parts of the body, although he did not know that it returned again to the heart, and thus was ignorant of what we now call the circulation. But he was the first to find that the heart is related to the blood-vascular system; and this he did by proving, in the way of dissection, that its cavities are continuous with those of the large veins and arteries. Nor did he end here. He traced the course of these large veins and arteries, giving an accurate account of their branchings and distribution. He knew perfectly well that arteries contain blood; and this is a matter of some importance, because it has been the habit of historians of physiology to affirm that all the ancients supposed arteries to contain air. In speaking of the cavities of the heart, he appears to have fallen into the unaccountably foolish blunder of saying that no animal has more than three, and that some animals have as few as one. But, although this apparent error has been harped upon by his critics, it is clearly no error at all. Professor Huxley has shown that what Aristotle here did was to regard the right auricle as a venous sinus, or as a part of the great vein, and not of the heart. The only mistake of any importance that he made in all his researches upon the anatomy of the heart and bloodvessels, was in supposing that the number of cavities of the heart is in some measure determined by the size of the animal. Here he undoubtedly lays himself open to the charge of basing a general and erroneous statement on a preconceived idea, without taking the trouble to test it by observation. But we may forgive him this little exhibition of negligence when we find that it was committed by the same observer, who correctly informs us that the heart of the chick is first observable as a pulsating point on the third day of incubation, or who graphically tells us that just as irrigating trenches in gardens are constructed to distribute water from one single source through numerous channels, which divide and subdivide so as to convey it to all parts, and thus to nourish the garden plants which grow at the expense of the water; so the blood-vessels start from the heart in a ramifying system, in order to conduct the nutritive fluid to all regions of the body. Lastly, Aristotle experimented on coagulation of the blood, and obtained accurate results as to the comparative rates with which the process takes place in the blood of different animals. He also correctly described the phenomenon as due to the formation of a meshwork of fibres; but he appears to have erroneously supposed that these fibres exist in the blood before it is drawn from the body. So much, then, for his views upon the heart, the blood, and the blood-vessels. He was less fortunate in his teaching about the bladder, kidneys, liver, spleen, and so forth, because he had no sufficient physiological data to go upon. Still, one would think he might have avoided the error of attributing the formation of urine to the bladder, seeing that he had gone so far as to perceive that the kidneys separate out the urine which, as he correctly says, then flows into the bladder. His chapters on the digestive tract display a surprisingly extensive and detailed investigation of the alimentary system of many animals; and the observations made are for the most part accurate. In particular, his descriptions of the teeth, esophagus, epiglottis, and the mechanism of deglutition, display so surprising an amount of careful and detailed observation throughout the vertebrated series, that they read much like a modern treatise upon these branches of comparative anatomy. The same remark applies to his disquisition on horns. Where inaccurate, his mistakes here are mostly due to his ignorance of exotic forms. Adipose tissue he correctly viewed as excess of nutritive matter extracted from the blood; and he noted that fatness is inimical to propagation. Marrow he likewise correctly regarded as having to do with the nutrition of bones; and observed that in the embryo it consists of a vascular pulp. That Aristotle should have had no glimmering notion either of the nervous system, or of its functions, is, of course, not surprising; but to me it is surprising that so acute an observer should have failed to perceive the physiological meaning of muscles. Although he knew that they are attached to bones, that they occur in greatest bulk where most strength of movement is required-such as in the arms and legs of man, the breasts of birds, and so forth, and although he must have observed that the muscles swell and harden when the limbs move, yet it never occurred to him to connect muscles with the phenomena of movement. He regarded them only as padding, having also in some way to do with the phenomena of sensation. Thus we appear to have one of those curious instances of feeble ob servation with which, every now and then, he takes us by surprise. To give parenthetically a still more strange example of what I mean, one would think that there is nothing in the economy of a star-fish or an echinus more conspicuous, or more calculated to arrest attention, than the ambulacral system of tube feet. Yet Aristotle, while describing many other parts of those animals, is quite silent about this ambulacral system. I think this fact can only be explained by supposing that he confined his observations to dead speci as if it were a living animal, and as if it were the beginning of all animals that have blood." mens; but, as he was not an inland naturalist, even this explanation does not acquit him of a charge of negligence, which, when contrasted with his custom- Turning now for a moment to Aristotle's ary diligence, appears to me extraordinary. still more detailed discoveries in compar. His ignorance of the nervous system ative anatomy and physiology, his most led him to a variety of speculative errors. remarkable researches are, I think, those In particular, he was induced to regard on the cetacea, crustacea, and cephathe heart as the seat of mind, and the lopoda. Here the amount of minute and brain as a bloodless organ, whose function accurate observation which he displayed it was to cool the heart, which he supposed is truly astonishing; and in some cases to be not only the organ of mind, but also his statements on important matters of an apparatus for cooking the blood, and by fact have only been verified in our own it the food. The respiratory system was century—such, for instance, as the peculalso conceived by him as a supplementary iar mode of propagation which has now apparatus for the purpose of keeping the been re-discovered in some of the cephabody cool - a curious illustration of early lopoda.* He also knew the anomalous philosophical thought arriving at a conclu- fact that in these animals the vitellus is sion which, to use his own terminology, joined to the mouth of the embryo; that was directly opposed to the truth. Never-in certain species of cartilaginous fish the theless, the reasoning which landed him in this erroneous conclusion was not only perfectly sound, but also based upon a large induction from facts, the observation of which is highly creditable. The reason why he supposed the office of respiration to be that of cooling the body was because nearly all animals which respire by means of lungs exhibit a high temperature, and, imagining that temperature or "vital heat was a property of the living soul, his inference was inevitable that the function of the lungs was that of keeping down the temperature of warm-blooded animals. Here, then, his error was due to deficiency of information, and the same has to be said of the great majority of his other errors. For instance, with regard to the one already mentioned about the heart being the seat of mind, this is usually said by commentators to have been due merely to the accident of the heart occupying a central position. And no doubt such was partly his reason, for he considered that position the noblest, and repeatedly argues that on this account it must be the seat of mind. But over and above this mystical, not to say childish reason, I think he must have had another. For seeing that the error is a very general one in early philosophical thought we find it running through the Psalms, and it is still conventionally retained by all poetic writers1 think we must look for some more evident reason than that of mere position to account for it. And this reason I take to be the perceptible influence on the heart-beat which is caused by emotions of various kinds. Furthermore, Aristotle expressly assigns the following as another of his reasons: "In the embryo the heart appears in motion before all other parts, embryo is attached to its parent by the intervention of a placenta-like structure; and, in short, detailed so many anatomical discoveries both as regards the vertebrata and invertebrata, that a separate article would be required to make them intelligible to a general reader. In this connec tion, therefore, I will only again insist upon the enormous difference between Aristotle and the great majority of his illustrious countrymen in respect of method. Unless it can be shown that an ancient writer has been led to anticipate the results of modern discovery by the legitimate use of inductive methods, he deserves no more credit for his guesses when they happen to have been right than he does when they happen to have been wrong. This, however, is a consideration which we are apt to neglect. When we find that an old philosopher has made a statement which science has afterwards shown to be true, we are apt to regard the fact as proof of remarkable scientific insight, whereas, when we investigate the reasonings which led him to propound the statement, we usually find that they are of a puerile nature, and only happened to hit the truth, as it were, by accident. Among a number of guesses made at random and in ignorance, a certain percentage may well prove right; but under these circumstances the man who happens to make a correct guess deserves no more credit than he who happens to have made an erroneous one. Indeed, he may deserve even less credit. For instance. when the Pythagoreans, on a basis of various mystical and erroneous speculations, propounded a kind of dim adumbra Lewes, however, denies that the evidence is suffi cient to show that Aristotle knew this. kingdom; and shows a profound penetration in drawing the true psychological distinction between him and the lower animals, namely, that animals only know particular truths, never generalize, or form abstract ideas. tion of the heliocentric theory, far from | drawing the boundary-lines between plants deserving any credit for superior sagacity and animals. For, while he correctly at the hands of modern science, they merit guessed, from erroneous observation, that condemnation for their extravagant theo- sponges should be classified as animals, rizing and unguarded belief. In their he decided in favor of placing the hydroid time, whatever evidence there was lay on polyps among the plants; and he appears the side of the then prevalent view that to have classified certain testaceous molthe sun moves round the earth. There- luscs in the same category. Man, of fore, when, without adducing any counter-course, he places at the head of the animal evidence of a scientific kind, they affirmed that the earth moved round the sun, they were merely displaying the spirit of what the Yankees call "pure cussedness." That is to say, they were shutting their eyes to the only evidence which was available, and showing their own obstinacy by propounding a directly opposite view. The sound maxim in science is, that he discovers who proves; and this is a maxim which many classical scholars would do well to remember when writing about the scientific speculations of the early Greeks. Now I have made these remarks in order again to emphasize the almost unique position which Aristotle holds among his contemporaries in this respect. Instead of giving his fancy free rein upon "the high priori road," he patiently plods the way of detailed research; and when he proceeds to generalize, he does so as far as possible upon the basis of his inductive experience. His conception of life was more in accordance with that of modern science than that of any of the other conceptions which have been formed of it either in ancient times or the Middle Ages. For he seems clearly to have perceived the error of regarding the "Vital Principle" otherwise than as an abstraction of our own making. Life and mind in his view were abstractions pertaining to organisms, just in the same way as weight and heat are abstractions pertaining to inanimate objects. For convenience of expression, or even for purposes of research, it may be desirable to speak of weight and heat as indepen. dent entities; but we know that they cannot exist apart from material objects that they are what we term qualities, and not themselves objects. And so with life and mind; they are regarded by Aristotle as qualities—or, as we should now say, Coming now to his generalizations, it was a true philosophical insight which enabled Aristotle to perceive in organic nature an ascending complexity of organi-functions of organisms. And here we zation from the vegetable kingdom up to must remember that the whole course of man. Instead of the three kingdoms of previous speculation on such matters pronature, which were afterwards formulated ceeded on the assumption that the vital by the alchemists, and which in general principle was an independent entity superparlance we still continue to preserve, added to organisms, serving to animate namely, the mineral, vegetable, and animal them as long as it was united to them, leav - instead of these three kingdoms, Aris- ing them to death and decay as soon as it totle adopted the much more philosophical was withdrawn from them; and even then classification of nature into two divisions, being itself able to survive as a disemthe organic and the inorganic, or the living bodied spirit, enjoying its conscious exand the not-living. Nevertheless, he fell istence apart from all material conditions. into the error - which was, indeed, al- Thus it was that the creations of early most unavoidable in his time-of sup- thought peopled the world with ghosts posing that there is a natural and a daily and spirits more numerously than nature passage of the one into the other. How had supplied it with living organisms. ever, he again shows his philosophical Now Aristotle boldly broke away from insight where he points out the leading this fundamental assumption of the vital distinctions between plants and animals, principle as an independent and superthe former manifesting life in the phe-added entity. In the phenomena of life nomena of nutrition alone, including and mind he saw merely the functions of germination, growth, repair, and repro- organism; he assigned to them both a duction; while the latter, besides these, exhihit also the phenomena of sensation, volition, and spontaneous movement. He was not so fortunate in his attempts at physical basis, and clearly perceived that for any fruitful study of either we must have recourse to the methods of physiol ogy. |