408 THE BEGINNINGS OF LIFE. 



ations with which they are undoubtedly associated., but 

 it may fairly enough be said that he is the advocate of 

 a doctrine which is irreconcilable with many other 

 facts generally admitted by chemists, and of one which 

 is thought by some of the most eminent of them to be 

 adverse to the best chemical knowledge of the day. 

 They hold the opinion (i) that fermentations cannot 

 be definitely and sharply discriminated from other 

 chemical changes not usually placed in this category 

 and (2) that amongst those chemical changes which are 

 generally considered to be real fermentations, there are 

 some whose occurrence is not necessarily associated 

 with the presence of organisms. 



If fermentative changes were, in reality, only to be 

 brought about through the agency of living organisms or 

 particles, how could we then account for the fact that 

 precisely such changes as are effected occasionally when 

 the influence of living particles might be predicated, 

 are at other times occasioned when no such predication 

 is tenable ? Thus, although pancreatin and pepsine 

 convert starch into sugar, a precisely similar change 

 may be brought about by dilute sulphuric acid; and 

 although saliva or emulsin may cause a breaking-up 

 or fermentation of salicine, here again dilute sulphuric 

 acid is capable of effecting a similar change. 



To take another instance, the production of acetic 

 acid is due to a process of fermentation, in which 

 alcohol is first converted into aldehyde and then into 

 the acid in question. This fermentative change, 



