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 these 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, from 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 dlustrate 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 Prime 
Vize; 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 ef 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 
