422 THE BEGINNINGS OF LIFE. 



growth and reproduction of the old, goes on simul- 

 taneously with the production of new living matter. 



Looked at from a chemical point of view, the most 

 essential feature of these changes seems to be that they 

 are successive, similar changes, induced by mere con- 

 tact with another body 1 . As we have previously stated, 

 however, such changes do not form a group apart, they 

 blend insensibly into chemical actions in general. 

 To speak of certain chemical changes, therefore, as 

 fermentations, as though they were different in kind 

 from other chemical changes, may be convenient, though 

 it must be acknowledged to be a mere arbitrary distinc- 

 tion, and not justifiable from a philosophical point of 

 view. Limiting ourselves, however, to such processes 

 as seem best entitled, in the opinion of Liebig and 

 others, to be included in this category, it appears to 

 me that, from one important point of view, they may 

 be included under three principal groups 2 . 



formed? (Liebig on Alcoholic Fermentation, loc. cit.) When a small 

 quantity of yeast is added to a simple solution of sugar, there can be 

 no new production of yeast either by growth or evolution, if no nitrogen 

 exists. 



1 See the definition of Pelouze and Fr^my at p. 402. Liebig says: 'We 

 can resolve with a given quantity of sulphuric acid unlimited quantities 

 of alcohol into ether and water ; we can, by the help of the same acid, 

 convert a quantity of starch into grape sugar, without the acid being 

 neutralized in either case. These effects are utterly distinct from the 

 effects produced when sulphuric acid acts on metals or metallic oxides ; 

 but it is quite absurd to ascribe them to a peculiar cause, altogether 

 different from chemical affinity.' (Letters on Chemistry, 1851. p. 263.) 



2 These views are submitted, with all deference, to the consideration of 

 chemists. 



