140 



LIFE. 



electricity, at least we have reason to believe it 

 is of a similar nature, and has the power of 

 regulating electrical operations." 



We shall now inquire into the precise import 

 attached to the term by those who continue to 

 employ it. It has been well remarked by 

 Mr. Mayo that the word principle, " charac- 

 teristic of a less advanced state of science, has 

 been generally employed (as the final letters of 

 the alphabet are used by algebraists) to denote 

 an unknown element, which, when thus ex- 

 pressed, is more conveniently analysed." Thus, 

 it has been customary to speak of the principle 

 of gravity, of electricity, or of magnetism, as 

 the unknown causes of certain phenomena, 

 whilst these are imperfectly comprehended. In 

 so far, however, as the laws of these pheno- 

 mena are understood; they terminate in referring 

 all the results to simple properties of matter, 

 from which they may be deduced by demon- 

 strative reasoning, just as geometrical theorems 

 from the postulates on which they are founded. 

 But in the science of physiology the term has 

 been employed in a less justifiable sense. It 

 must be admitted on all hands, that the condi- 

 tions of vital phenomena are not yet determined 

 with sufficient precision to enable us to refer 

 all observed facts, through the medium of 

 general laws, to simple vital properties ; and 

 there would be no objection, save the proba- 

 bility of its abuse, to the employment of the 

 term " Vital Principle," like " Nisus formati- 

 vus" or " Organic Force," as a convenient ex- 

 pression for the sum of the unknown powers 

 which are developed by the action of these 

 properties. But to this limit physiologists 

 have unfortunately not restricted themselves. 

 They have regarded it as a distinct entity en- 

 dowed with properties of its own, in virtue of 

 which it acts upon matter,- removing its par- 

 ticles from the pale of physical and chemical 

 laws, transforming them into organised tis- 

 sues, endowing these tissues with new pro- 

 perties, prompting their actions, preserving 

 their composition in defiance of external in- 

 fluences which would tend to disintegrate them, 

 and finally quitting them, or being itself 

 worn out with them, so as to leave the frame- 

 work without its protecting influence, deprived 

 of which it speedily falls to decay. 



Of the character of this principle, its expo- 

 sitors leave us very much in the dark. Of all 

 modern writers, Dr. Prout is probably the one 

 who has most plainly expressed himself on it. 

 In his Gulstonian Lectures* he informs us that, 

 " In all cases it must be considered an ultimate 

 principle, endowed by the Creator with a 

 faculty little short of intelligence, by means of 

 which it is enabled to construct such a mecha- 

 nism, from natural elements, and by the aid of 

 natural agencies, as to render it capable of 

 taking further advantage of their properties, 

 and of making them subservient to its use." 

 The fallacies involved in this supposition have 

 been elsewhere so ably exposedf that we shall 

 not here stop to discuss it; but in our survey 



* Medical Gazette, vol. viii. p. 261. 



t Roberton on Lite and Mind, p. 36 et seq. 



of the nature and causes of vital actions, we 

 shall take occasion to inquire whether any such 

 hypothesis is called for, or whether it is not 

 worse than useless by complicating what is 

 otherwise readily explicable on simple and phi- 

 losophical principles. 

 III. NATURE AND CAUSES OF VITAL ACTION. 



It has been already pointed out that all the 

 changes in the external world are the results of 

 the properties of inorganic matter, called into 

 exercise by the means appropriate to excite or 

 stimulate each to activity; and we may further 

 observe that these means are different for each 

 property. Thus, to develope the dormant pro- 

 perty of gravitation in any mass of matter, we 

 should only have to bring it within the sphere of 

 attraction of any other mass. But to develope 

 the dormant electrical property of a loadstone, 

 a mass of iron alone would serve. Every 

 operation in chemistry is founded- upon the 

 same principle, each substance acted upon 

 being capable of responding, in a manner 

 peculiar to itself, to the influence of agents 

 brought to bear upon it. Now, however fami- 

 liar this idea may seem, it has been too much 

 neglected in the investigation of vital pheno- 

 mena; and notwithstanding that we always 

 find a similarity of action, when the organised 

 structure, on the one hand, and the stimuli 

 which call its properties into activity, on the 

 other, are identical and a difference in either 

 of these conditions always producing a diffe- 

 rence in the result, physiologists have been in 

 the habit of looking to some other agency for 

 the cause of the variation. It is true that we 

 occasionally meet with instances in which the 

 result is different, without our being able to 

 detect any change in either of the conditions ; 

 but, knowing as we do how very slight an 

 alteration in the structure of a tissue or organ 

 will at once destroy or entirely change its vital 

 properties, we cannot wonder that they should 

 undergo important modifications without their 

 sources being perceptible to our present means 

 of research ; and, as will hereafter be more 

 fully shown, every extension of our powers of 

 observation renders this doctrine more probable. 



When we analyse the mass of phenomena 

 which are presented to us by the vital actions 

 of the organised world, we find that they are 

 susceptible of reduction into distinct classes, 

 by which the study of them is much facilitated. 

 Thus, all living beings introduce into their 

 own structure alimentary materials derived from 

 external sources ; and all likewise submit their 

 fluid ingredients to the influence of the element 

 they inhabit, in such a manner that a reciprocal 

 change occurs between them. In this mode 

 we arrive at the notion of the distinct Junctions 

 of living beings, each of which may be 

 regarded (in its simplest form) as a group of 

 phenomena of similar character and referable 

 to the same causes. Thus, the function of 

 respiration, when stripped of all the acts some- 

 times associated with it, is essentially the same 

 throughout the whole organized world ;* and 

 the simplicity of the changes involved in it, 



* See Prin. of Gen. and Comp. Phys. ch. ix. 



