280 Dr Alison on the Principle of Vital Affinity. 



decomposition of w^ater and evolution of the hydrogen by iron 

 and acid, — but simply because it indicates an affinity peculiar 

 to the state of life ; — ^because in no other circumstances, 

 when the elements of 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 en- 

 ables oxygen and hydrogen to unite and form water, or the 

 presence of fermenting yeast enables sugar to undergo trans- 

 formation 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 matter, from a compound 

 fluid, to those cells, and likewise the formation of other com- 

 pounds 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 inevitably 

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

 principle of catalysis may be said to illustrate the transfor- 

 mations in living bodies, as that of endosmose illustrates the 

 selection and appropriation of chemical elements or com- 

 pounds in living structures ; but these principles, as exempli- 

 fied in dead matter, 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 generally fonnd to have been prepared for them 

 by vegetables, that it has been reasonably 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 ac- 

 tion 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 Primae Vise ; yet it never 

 appears in the chyle, nor, in the natural state, in the blood ; 



