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SCIENCE. 



[Vol. XVII. No 422 



and harmony as the final end or aim of all her work. He appears, 

 however, clearly to have recognized, 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 vvas 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 ar- 

 gument in Cavor of design. On the other hand, it is certain that 

 ne would have differed from these theologians in one important 

 particular; for he everywhere regards the purposes of Nature as 

 operating under limitations imposed by what he calls absolute 

 necessity. Monsters, for example, he says are not the intentional 

 work of Nature herself, but instances of the victory of matter over 

 Nature; that is to say, they are instances where Nature has failed 

 to' satisfy those .conditions of necessity under which she acts. 

 Thus, even if there be a disposing mind which is the author of 

 Nature, according to Aristotle it is not the mind of a creator, but 

 rather that of an architect, who does the best he can with the 

 materials supplied to him, and under the conditions imposed by 

 necessity. 



Turning, now, to the actual work which Aristotle accomplished 

 in the domain of biology, I will first enumerate his more impor- 

 tant discoveries upon matters of fact, and then proceed to men- 

 tion his more important achievements in the way of generalization. 

 He correctly viewed the blood as the medium of general nutri- 

 tion, 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 dis- 

 tribution. 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 fool- 

 ish blunder of saying that no animal has more than three, and 

 that some animals have as few as one. But, although this ap- 

 parent 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 reseai-ches upon the anatomy 

 of the heart and blood-vessels, was in supposing that the number 

 of caviiies 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 precon- 

 ceived 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 cor- 

 rectly informs us that the heart of the chick is first observable as 

 a pulsating point on the third day of incubation, or who graphi- 

 cally tells us that just as irrigating trenches in gardens are con- 

 structed 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 phe- 

 nomenon 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 jihysiological 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 systems of many animals, and the observations 

 made are for the most part accurate. In particular, his descrip- 

 tions of the teeth, oesophagus, epiglottis, and the mechanism of 

 deglutition, display so .surprising an amount of careful and de- 

 tailed observation throughout the vertebrated series, that they 

 read much like a modern treatise upon these branches of com- 

 parative 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 surpris- 

 ing; but to me it is surprising chat 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 re- 

 quired, — such as in the arms and legs of man, the breasts of birds, 

 and so forth, — and although he must have observed that the mus- 

 cles 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 cui-ious instances of feeble observation with which 

 every now and then he takes us by surprise. To give paren- 

 thetically 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 

 echiniis 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 specimens; 

 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 customary diligence, appears to me extraor- 

 dinary. 



His ignorance of the nervQjis system led him to a variety of 

 speculative errors. In particular, he was induced to regard the 

 heart as the seat of mind, and the brain as a bloodless organ, 

 whose function it was to cool the heart, which he supposed to be 

 not only the organ of mind, but also an apparatus for cooking the 

 blood, and by it the food. The respiratory system was also con- 

 ceived by him as a supplementary apparatus for the purpose of 

 keeping the body cool, — a curious illustration of early philo- 

 sophical thought arriving at a conclusion which, to use his own 

 terminology, was directly opposed to the truth. Nevertheless, 

 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 cool- 

 ing 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. Fi3r in- 

 stance, 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 vvas partly his reason, for he 



