Dr Alison on the Principle of Fital Affinity. 279 



chanical, or simply attractive power, by which cells or other 

 organs are formed out of amorphous matter, and likewise the 

 chemical powers with which these cells are endowed. 



It is no objection to what has been stated, of the strictly 

 vital nature of these chemical powers, to admit that their ac- 

 tion is very often analogous to the principle to which the name 

 catalysis is given by chemists, and which is exemplified like- 

 wise in the chemistry of inorganic compounds, where the com- 

 bination of two substances is determined by the presence of 

 a third, which nevertheless takes no part in the combination 

 itself; or that it is analogous to that disturbance of the equi- 

 librium of chemical compounds, by which the fermentation of 

 an organic compound is transferred to another in contact with 

 it, although the changes in the two go on separately, and the 

 compounds formed are different. It is quite true, that those 

 modes of chemical action resemble and illustrate the man- 

 ner in which living solids, themselves undergoing continual 

 changes of composition, determine new arrangements of the 

 elements of the compound fluids which are brought in con- 

 tact with them. But this analogy is far from being an ex- 

 planation or resolution of the one phenomenon into the other. 

 In the first place, the analogy is essentially defective ; be- 

 cause although it is true that in any living being, already ex- 

 isting, different chemical compounds already exist in different 

 parts of the structure, which may act in these modes on the 

 nourishing fluid, and determine distinct transformations of 

 these at different parts ; yet this does not apply, as already 

 observed, to the first formation of each of the textures, at its 

 appropriate point, from a homogeneous semifluid matter. 

 But farther, although we were to admit the analogy of all the 

 chemical processes going on in living beings, to these forms 

 of simply chemical action, we should not thereby be autho- 

 rised to conclude that the vital processes have not that pecu- 

 liarity which makes it incumbent on us to regard them as a 

 separate class. We say that the decomposition of carbonic 

 acid, the combination of the carbon with the elements of water 

 to form starch, and the evolution of the oxygen, is a vital ac- 

 tion, — not because it is a change different in kind from the 



