FERMENTS AND ARTIFICIAL FERMENTATIONS. 67 



properly so called, either by means of a nitrogenous 

 substance of animal origin (Berthelot), or by other 

 chemical and physical processes which we shall 

 presently mention. But it may be questioned whether 

 the nitrogenous substance of animal origin, which 

 Berthelot considers to be dead, does not contain a 

 living ferment. This is not admitted to be the case 

 by B^champ, whose theory will be given further on. 



Whenever fermentation is produced solely by the 

 influence of physical and chemical agents, the action 

 is very slow. But it is, on the other hand, very rapid 

 when effected by living ferments or yeast, and it is 

 also much less costly, so thalPthe latter mode of 

 fermentation is preferred by manufacturers. Yeast is, 

 therefore, the true agent in artificial fermentations. 



All the saccharine liquids which contain glucose or 

 grape sugar, or a sugar which can be transformed into 

 glucose, and also all nitrogenous substances, phos- 

 phates, and ammoniacal salts, produce alcohol at a 

 temperature varying between 25° and 100°, and the 

 yeast of beer (of which the spores are carried through 

 the air) appears and is developed at the same time; 

 this occurs in the juice of grapes, beetroot, sugar- 

 cane, etc. The alcoholic liquids thus produced are 

 then subjected to distillation in order to extract the 

 alcohol. The transformation of alcohol into vinegar 

 is produced by another ferment. 



Fermentations are very common in nature. The 

 transformation of sugar into lactic, butyric, and 



