PHYSIOLOGY. 



ers, that they can, by no means, be ex- 

 plained by the physical, mechanical, or 

 chemical qualities of matter. Yet the 

 operation of the latter can be clearly dis- 

 cerned in many instances in the animal 

 economy ; thus the humours of the eye 

 variously affect the rays of light according 

 to their figure and density : and the me- 

 chanical elasticity of the epiglottis, and 

 the chemical affinities exercised in respi- 

 ration, are further examples to the sume 

 effect. Yet the energy and power of 

 the vital force is most clearly evinced in 

 resisting and overcoming, as we have 

 already stated, the common laws of mat- 

 ter. Stahl and his followers, were so 

 struck with the circumstance of living 

 bodies resisting those affinities, which 

 produce putrefaction in dead animal mat- 

 ter, that they made life itself to consist in 

 this antiseptic property. The celebrated 

 experiment of Borelli, in which a muscle, 

 deprived of life, was immediately torn 

 by a weight which it could lift easily du- 

 ring life, shows how the laws of gravity 

 are overcome. This vital power, in the 

 explanation and illustration of which all 

 physiology is concerned, is so apparent in 

 every living process, that it has been 

 observed by the physiologists of every 

 age, although designated by very various 

 appellations, and defined in very different 

 ways. Calidum innatum, archseus, spiritus 

 vitalis, principium senliens, &c. are 

 among its numerous appellations. Let it 

 be remembered, that neither these, nor 

 the phrases of vital principle, &c. express 

 any being existing by itself, and inde- 

 pendently of the actions by which it is 

 manifested ; they are only to be consider- 

 ed as denoting the assemblage of powers 

 that animate living bodies, and distinguish 

 them from inert matter. Some writers, 

 realizing the offspring of a mere abstrac- 

 tion, have talked of the living principle 

 as something distinct from the body, to 

 which they have ascribed powers of see- 

 ing and feeling, and even of acting with 

 design. 



A more close inspection of any living 

 body will speedily convince us, that this 

 force, which holds together its compo- 

 nent parts, in spite of the external pow- 

 ers, which tend to separate them, does 

 not confine its influence to this passive 

 result, but that its operation extends even 

 beyond the limits of the living body itself. 

 It seems, at least, that this power does 

 not differ from that by which new parti- 

 cles are attracted, and interposed between 

 i the old constituent ingredients of the 

 body; the latter effect seeming to be ex- 

 erted as constantly as the power by which 



the materials of the body are held to- 

 gether. For, besides the absorption of 

 alimentary matter from the intestines, and 

 its entrance into the circulating fluid, 

 carrying it to all parts, which processes 

 experience no interruption, but are con- 

 tinued from one meal to another, there 

 is another kind of absorption constantly 

 going on from the surface of the body, 

 and a third which takes place by means 

 of respiration. The two latter alone exist 

 in such living bodies as have not the func- 

 tion of digestion ; viz. in plants. Now, 

 since living bodies do not grow indefi- 

 nitely, but have certain limits assigned by 

 nature to their size ; they must lose on 

 one side at least, a large part of what 

 they receive on the other ; and, in fact, 

 attentive observation shows us, that per- 

 spiration, and several other processes, 

 are constantly destroying parts of their 

 substance. 



Hence the idea which we formed at 

 first of the principal phenomenon of life, 

 must be considerably modified. Instead 

 of a constant union of the composing par- 

 ticles, we observe them in a state of con- 

 tinual circulation from without inwards, 

 and from within outwards. Thus, a living 

 body is a structure into which dead par- 

 ticles are successively brought, for the 

 purpose of combining together in various 

 ways, occupying places and exercising 

 offices determined by the nature of the 

 combinations into which they enter, and 

 departing, after a certain period, to be 

 brought under the action of those laws 

 which regulate inanimate matter. We 

 must observe, however, that the propor- 

 tion of particles, entering into, or quitting 

 the system, varies according to the age 

 and health of the individual, and that the 

 velocity of the general motion differs ac- 

 cording to the different states of each liv- 

 ing body. 



It appears, too, that life is arrested by 

 causes similar to those which interrupt 

 other known kinds of motion ; and that 

 the induration of fibres, and obstruction 

 of vessels, would render death an inevita- 

 ble consequence of life, as rest necessa- 

 rily follows all movements which are not 

 performed in vacuo, even if the hour of 

 its approach were not hastened by a mul- 

 titude of extraneous causes. 



This general and common motion of all 

 parts constitutes the very essence of life, 

 insomuch that parts separated from a 

 living body immediately die, because they 

 have no power of motion within them- 

 selves, and only participate in the general 

 motion produced by the assemblage. 

 Thus, the peculiar mode of existence ojf 



