140 Dr Alison on the Principle of Vital Affinity. 



vegetable, that this peculiar chemical change, under the ac- 

 tion of light, is effected ; the same fluid, introduced into cells 

 composed of the same material in the parts of fructification, 

 undergoes no such change ; but, on the contrary, gives occa- 

 sion only to the reverse process, the absorption of oxygen 

 and evolution of carbonic acid.* 



Then it is to be remembered, that this complete inversion 

 of ordinary chemical affinities, in the case of the living plant, 

 is only one of several cases to be afterwards noticed, where 

 we see chemical compounds uniformly formed in living bodies, 

 quite distinct from any that can be formed by the chemist 

 from the same elements, and quite distinct from those to 

 which the same elements uniformly revert, after the pheno- 

 mena of life are over. 



Lastly, we must remember, when we see this apparent in- 

 version or alteration of the ordinary chemical relations of 

 matter, taking place in the interior of living bodies, that in 

 that scene, by the admission of all, matter comes under the 

 dominion of mechanical laws, which operate in no other de- 

 partment of nature ; so that it is quite conformable to analogy 

 to suppose that its chemical relations will undergo a similar 

 modification. 



When all these considerations are duly weighed, I cannot 

 perceive what further evidence can be required in order to 

 justify the expression which I have quoted from Liebig, viz., 

 that the " new combinations,''^ as well as the forms, assumed 

 by that matter which goes to the composition of organized 

 beings, " indicate the existence of a power distinct from all 

 other powers of nature, viz., the vital principle ;" i. e., that 

 the vital principle regulates the changes of chemical composi- 

 tion, as well as the changes of position which the particles of 

 that matter undergo ; which is more simply expressed by say- 

 ing, that there are vital affinities as well as vital contractions 

 and attractions. 



But even if we are to regard it as doubtful whether or not 

 ordinary chemical affinities can determine, under any condi- 



* Theodore de Saueeurc, in Jameson's Edinburgh Philosophical Journal, 

 vol. xl., pp. 22, 23. 



