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SCIENCE. 



chanical explanation of its contraction by the influx of 

 animal spirits. 



" The discoveries of Trembley tended in the same direc- 

 tion. In the fresh water Hydra no trace was to be found 

 of that complicated machinery upon which the perfor- 

 mance of the functions in the higher animals was sup- 

 posed to depend. And yet the hydra moved, fed, grew, 

 multiplied, and its fragments exhibited all the powers of 

 the whole. And, finally, the work of Caspar F. Wolff,* 

 by demonstrating the fact that the growth and develop- 

 ment of both plants and animals take place antecedently 

 to the existence of their grosser organs, and are, in fact, 

 the causes and not the consequences of organization (as 

 then understood), sapped the foundations of the Cartesian 

 physiology as a complete expression of vital phenomena. 

 For Wolff, the physical basis of life is a fluid, possessed 

 of a " vis essentialis ' and a ' solidescibilitas ; ' in virtue of 

 which it gives rise to organization ; and, as he points out, 

 this conclusionstrikes at the root of the whole iatro-me- 

 chamcal system. 



" In this country the great authority of John Hunter 

 exerted a similar influence, though it must be admitted 

 that the too sibylline utterances which are the outcome 

 of Hunter's struggles to define his conceptions are often 

 susceptible of more than one interpretation. Neverthe- 

 less, on some points Hunter is clear enough. For ex- 

 ample, he is of opinion that ' spirit is only a. property of 

 matter '(' Introduction to Natural History,' page 6), he 

 is prepared to renounce animism (1. c, p. 8), and his con- 

 ception of life is so completely physical that he thinks of 

 it as something which can exist in a state of combination 

 in the food. ' The aliment we take in has in it, in a fixed 

 state, the real life, and this does not become active until 

 it has got into the lungs, for there it is freed from its 

 prison' (Observations on Physiology,' p. 113). He also 

 thinks that : ' It is more in accord with the general 

 principles of the animal machine to suppose that none of 

 its effects are produced from any mechanical principle 

 whatever, and that every effect is produced from an 

 action in the part, which action is produced by a stimulus 

 upon the part which acts, or upon some other part with 

 which this part sympathizes, so as to take up the whole 

 action ' (1. c, p. 152). And Hunter is as clear as Wolff, 

 with whose work he probably was unacquainted, that 

 ' whatever life is, it most certainly does not depend upon 

 structure or organization ' (1. c. p. 114). 



" Of course, it is impossible that Hunter could have in- 

 tended to deny the existence of purely mechanical opera- 

 tions in the animal body. But while with Borelh and 

 Boerhaave, he looked upon absorption, nutrition, and 

 secretion as operations effected by means of the small 

 vessels, he differed from the mechanical physiologists, 

 who regarded these operations as the result of the me- 

 chanical properties of the small vessels, such as the size, 

 form, and disposition of their canals and apertures. 

 Hunter, on the contrary, considers them to be the effect 

 of properties of these vessels which are not mechanical, 

 but vital. ' The vessels,' says he, ' have more of the 

 polypus in them than any other part of the body,' and he 

 talks of the ' living and sensitive principles of the ar- 

 teries,' and even of the ' dispositions or .feelings of the 

 arteries.' ' When the blood is good and genuine, the 

 sensations of the arteries, or the dispositions for sensa- 

 tion, are agreeable. . . . It is then they dispose of 

 the blood to the best advantage, increasing the growth 

 of the whole, supplying any losses, keeping up a due suc- 

 cession, etc' (I, c, p. 133). 



" If we follow Hunter's conceptions to their logical 

 issue, the life of one of the higher animals is essentially 

 the sum of the lives of all the vessels, each of which is a 

 sort of physiological unit, answering to a polyp ; and, as 

 health is the result of the normal "action of the vessels," 

 so is disease an effect of their abnormal action. Hunter 



thus stands in thought, as in time, midway between Borelli, 

 on the one hand, and Bichat, on the other. The acute 

 founder of general anatomy, in fact, outdoes Hunter 

 in his desire to exclude physical reasonings from the 

 realm of life. Except in the interpretation of the action 

 of the sense organs, he will not allow physics to have 

 anything to do with physiology. ' To apply the physical 

 sciences to physiology is to explain the phenomena of 

 living bodies by the laws of inert bodies. Now, this is a 

 false principle, hence all its consequences are marked 

 with the same stamp. Let us leave to chemistry its 

 affinity, to physics its elasticity and its gravity. Let us 

 invoke for physiology only sensibility and contractility ' * 

 Of all the unfortunate dicta of men of eminent abil- 

 ity this seems one of the most unhappy, when we 

 think of what the application of the methods and the 

 data of physics and chemistry has done towards bringing 

 physiology into its present state. It is not too much to 

 say that one half of a modern text-book of physiology 

 consists of applied physics and chemistry, and that it is 

 exactly in the exploration of the phenomena of sensibility 

 and contractility that physics-and chemistry have, exerted 

 the most potent influence. 



" Nevertheless, Bichat rendered a solid seivice to phy- 

 siological progress by insisting upon the fact that what 

 we call life in one of the higher animals is not an invis- 

 ible unitary archaeus dominating from its central seat the 

 parts of the organism, but a compound result of the syn- 

 thesis of the separate lives of those parts. ' All animals,' 

 says he, ' are assemblages of different organs, each of 

 which performs its function and concurs, after its fashion, 

 in the preservation of the whole. They are so many 

 special machines in the general machine which consti- 

 tutes the individual. But each of these special machines 

 is itself compounded of many tissues of very r different 

 natures, which, in truth, constitute the elements of these 

 organs (1. c, lxxix.) The conception of a proper vitality 

 is applicable only 1o these simple tissues, and not to the 

 organs themselves (1. c, lxxxiv.).' And Bichat proceeds 

 to make the obvious application of this doctrine of syn- 

 thetic life, if I may so call it, to pathology. Since dis- 

 eases are only alterations of vital properties, and the 

 properties of each tissue are distinct from those of 

 the rest, it is evident that the diseases of each tissue 

 must be different from those of the rest. Therefore, in 

 any organ composed of different tissues, one may be dis- 

 eased and the other remain healthy, and this is what 

 happens in most cases (1. c, lxxxv.). In a spirit of true 

 prophecy, Bichat says : ' We have arrived at an epoch 

 in which pathological anatomy should start afresh.' For, 

 as the analysis of the organ had led him to the tissues as 

 the physiological units of the organism, so, in a succeed- 

 ing generation, the analysis of the tissues led to the cell 

 as the physiological element of the tissues. The con- 

 temporaneous study of development brought out the 

 same result, and the zoologists and botanists, exploring 

 the simplest and the lowest forms of animated beings, 

 confirmed the great induction of the cell theory. Thus 

 the apparently opposed views which have been battling 

 with one another ever since the middle of the last cen- 

 tury have proved to be each half a truth. 



" The proposition of Descartes, that the body of a 

 living man is a machine, the actions of which are explic- 

 able by the known laws of matter and motion, is un- 

 questionably largely true. But it is also true that the 

 living body is a synthesis of innumerable physiological 

 elements, each of which may nearly be described in 

 Wolff's words, as a fluid possessed of a vis essentialis, 

 and a solidescibilitas ; or, in modern phrase, as proto- 

 plasm susceptible of structural metamorphosis and func- 

 tional metabolism ; and that the only machinery, in the 

 precise sense in which the Cartesian school understood 

 mechanism, is that which co-ordinates and regulates 



% Theoiis Generations, 1759. 



* Anatomie generate, i., p. liv. 



