THE PRINCIPLE OF VITAL AFFINITY. 181 



■water are brought into contact with carbonic acid, is any such decomposition 

 effected. So also, although it is true that the presence of spongy platinum enables 

 oxygen and hydrogen to unite and form water, or the presence of fermenting 

 yeast enables sugar to undergo transformation into carbonic acid and alcohol, 

 still tliese facts do not interfere with those essential peculiarities on which the 

 doctrine of vital affinity depends, viz., that the presence of living cells composed 

 of carbon and the elements of water, determines both the addition of new mat- 

 ter, fi'om a compound fluid, to those cells, and likewise the formation of other 

 compounds within the cells, varying in different parts of the same structure, — 

 all these compounds being different from any which the chemist can form out of 

 the same elements, and different from those to which the same elements inevi- 

 tably return, after the phenomena of life are over. The physical principle of 

 catalysis may be said to illustrate the transformations in living bodies, as that of 

 endosmose illustrates the selection and appropriation of chemical elements or 

 compounds in living structures ; but these principles, as exemplified in dead mat- 

 ter, include none of the peculiarities of the vital chemical actions, and therefore 

 furnish no explanation of them. 



The materials of which animal bodies are composed, have been now so gene- 

 rally found to have been prepared for them by vegetables, that it has been rea- 

 sonably doubted, whether any such power of decomposing the fluids presented to 

 them, and forming new compounds, exists in animals. There are some cases, 

 however, in which it appears certain that an action of this kind goes on in living 

 animals, and that it is effected, as in vegetables, by an agency of cells. Thus, there 

 is good evidence that, in the natural state, much of the bile which is discharged 

 into the intestines from the liver is re-absorbed in its passage along the Primte 

 Viae ; yet it never appears in the chyle, nor, in the natural state, in the blood ; 

 which seems to imply that it is decomposed, and its elements thrown into other 

 combinations, in the course of the cellular action which attends the absorption of 

 chyle. 



In like manner, the formation of fatty compounds out of starch, or its kin- 

 dred principles, as illustrated by the recent precise observations on the formation 

 of wax by bees, and the formation of gelatine in the living animal, are undoubted 

 instances of chemical transformations thus effected. The precise scene of these 

 transformations is not yet ascertained, but we have strong reason from analogy 

 to suppose that they are effected in the course of the circulation. And as we are 

 certain that the greatest of all the chemical changes which are peculiar to living 

 beings are effected within the cells of vegetables, it seems in the highest degree 

 probable, that the corpuscles or cells (both red and white) which form so large a 

 part of the blood of animals, are concerned in the chemical transformations which 

 take place in blood ; and therefore, that we are to regard organized and liv- 

 ing cells as the agents or instruments employed by nature in effecting all those 

 chemical changes which are peculiar to the state of life. And if we consider this 



VOL. XVI. PART II. 2 Z 



