THEORY OF FERMENTATION 327 



quence of its ability to derive the carbonaceous part of its 

 food from very different substances, from sugar, or lactic 

 acid, or glycerine, or mannite, and many others. 



When we say that every fermentation has its own pe- 

 culiar ferment, it must be understood that we are speaking 

 of the fermentation considered as a whole, including all the 

 accessory products. We do not mean to imply that the fer- 

 ment in question is not capable of acting on some other fer- 

 mentable substance and giving rise to fermentation of a 

 very different kind. Moreover, it is quite erroneous to sup- 

 pose that the presence of a single one of the products of 

 a fermentation implies the co-existence of a particular fer- 

 ment. If, for example, we find alcohol among the products 

 of a fermentation, or even alcohol and carbonic acid gas to- 

 gether, this does not prove that the ferment must be an 

 alcoholic ferment, belonging to alcoholic fermentations, in 

 the strict sense of the term. Nor, again, does the mere 

 presence of lactic acid necessarily imply the presence of 

 lactic ferment. As a matter of fact, different fermenta- 

 tions may give rise to one or even several identical products. 

 We could not say with certainty, from a purely chemical 

 point of view, that we were dealing, for example, with an 

 alcoholic fermentation properly so called, and that the yeast 

 of beer must be present in it, if we had not first determined 

 the presence of all the numerous products of that particular 

 fermentation under conditions similar to those under which 

 the fermentation in question had occurred. In works on 

 fermentation the reader will often find those confusions 

 against which we are now attempting to guard him. It 

 is precisely in consequence of not having had their attention 

 drawn to such observations that some have imagined that 

 the fermentation in fruits immersed in carbonic acid gas 

 is in contradiction to the assertion which we originally made 

 in our Memoir on alcoholic fermentation published in 1860, 

 the exact words of which we may here repeat: "The 

 chemical phenomena of fermentation are related essentially 

 to a vital activity, beginning and ending with the latter; we 

 believe that alcoholic fermentation never occurs " we were 

 discussing the question of ordinary alcoholic fermentation 

 produced by the yeast of beer " without the simultaneous 



