LIFE. 



147 



together with the facility with which it may be 

 made the subject of experiment, render our 

 knowlege of its character and conditions nearly 

 complete. 



When we have analysed these groups of 

 vital phenomena and satisfied ourselves of the 

 conditions under which they occur, we are 

 brought to the conclusion that for each a parti- 

 cular organ or species of structure is appro- 

 priated in the organized system, and that its 

 action is dependent upon the excitation of its 

 properties by agents external to it, just as in 

 the inorganic world. This dependence of life 

 upon external stimuli has been completely 

 overlooked by the advocates of the vital prin- 

 ciple ; and it is probably to Brown, with all his 

 faults and absurdities, that we owe the first 

 prominent enunciation of the fact. When these 

 stimuli are withdrawn, vital action ceases ; 

 though, under favourable conditions, vitality 

 or the vital properties of the organism may be 

 retained. (Sect. VI.) 



Every class of organs in the living body may 

 be said to require its particular stimulus for the 

 display of its properties. Thus, regarding the 

 whole structure as a series of assimilating 

 organs capable of converting nutrient mate- 

 rials into structures like their own, and of thus 

 causing them to exhibit vital properties we 

 may say that the supply of these nutrient ma- 

 terials in a fluid state is the stimulus to their 

 action. Again, to the excretory organs the 

 required stimulus is the presence of certain 

 superabundant and therefore injurious elements 

 in the nutritious fluid . To the action of the 

 muscular system the excitement of innervation, 

 or the application of a physical stimulus, is 

 necessary. In all classes of living beings we 

 find these functional changes performed under 

 conditions which are essentially the same ; and 

 hence we are enabled to arrive at the laws 

 which regulate each. 



These are not the only conditions required, 

 however; for others of a still more general 

 nature are constantly, and therefore impercepti- 

 bly, operating. All vital actions, for example, 

 require a certain amount of heat for their per- 

 formance, and the amount varies in different 

 cases. This is no more, however, than what 

 we meet with in the inorganic world ; for many 

 chemical and physical operations can only take 

 place within certain limits of temperature, and 

 these sometimes very circumscribed. The pre- 

 sence of light, again, is essential to many others, 

 especially in the vegetable kingdom ; but this, 

 again, finds its parallel in the inorganic world, 

 many chemical decompositions (which indeed 

 bear a remarkable analogy with the changes 

 which this agent produces in the green parts of 

 plants when exposed to an atmosphere contain- 

 ing carbonic acid) being due to its influence. 

 And although, with regard to electricity as a 

 vital stimulus, our absolute knowledge is still 

 less, what we do know leads to the belief that 

 it is an agent of at least as much importance 

 in the vital economy as in the operations of in- 

 organic nature. 



There is nothing, then, in the nature or con- 

 ditions of vital actions considered individually, 



which need cause us to reason upon them in 

 any other way than we do upon the phenomena 

 of the inorganic world ; and it is obviously 

 unphilosophical to assume an agency which is 

 not required to account for them. It must be 

 recollected, too, that the onus probandi rests 

 with those who make the assumption, and not 

 with those who maintain the analogy in the 

 character of vital phenomena to those of the 

 universe at large. The assumption may be 

 easily shown to be not only useless, but insuffi- 

 cient to explain phenomena without calling to 

 its aid the very principles which have been 

 shown to be themselves competent. Thus, the 

 physiologist who traces the operation of the 

 vital principle in the function of secretion, is 

 compelled to allow that, as by one principle so 

 great a variety of products are eliminated by 

 the various glands from one material, the diffe- 

 rence in the results must be due to some 

 difference in the structure of the organs respec- 

 tively concerned. And it may then be fairly 

 inquired of him, " If the difference in the 

 glandular structure and action is capable of 

 giving rise to so great a variety in the products, 

 with the cooperation of this one vital principle, 

 how can it be proved that this difference in the 

 glandular structure and action may not be capa- 

 ble of giving rise to the same result by itself, and 

 without the aid of any such adjunct at all?"* 

 A similar question might be put with regard to 

 any other class of actions, in which, under the 

 same general conditions, the results are modified 

 by the peculiar characters of the instruments or 

 organs respectively employed ; and, as a nega- 

 tive reply must be given equally to all, it may 

 be safely affirmed that no reasoning can deduce 

 the doctrine of a vital principle from the phe- 

 nomena of life separately considered. 



But the advocates of the doctrine rely much 

 upon the peculiar adaptation of the various 

 changes taking place in each being to the pur- 

 poses of its existence ; and assume that this 

 adaptation can only result from the control 

 of a subordinate presiding agent constantly 

 exercised over each. Here, again, we find 

 such a doctrine not only unsupported by, but 

 manifestly inconsistent with, the analogies of 

 nature. No reflecting mind has any doubt 

 that this earth and its inhabitants form a system, 

 of which every part is perfectly adapted to the 

 rest, (so that we might almost call it an or- 

 ganised one, if the idea of a particular struc- 

 ture were not involved in the term,) and of 

 which all the actions and changes, however in 

 appearance contrary, have one common ten- 

 dency the ultimate happiness of the creatures 

 of Infinite Benevolence. The same may be 

 said of it in regard to its relations with the 

 system of which it forms a part ; and probably 

 of that system with regard to the universe in 

 which it is but a speck. So far as we can un- 

 derstand the working of the laws by which that 

 universe is governed, we see them all mutu- 

 ally adapted to the same ends, whether we 

 consider the welfare of the whole system, or of 

 our own comparatively insignificant planet, with 



* Prichard on the Vital Principle, p. 100. 



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