ALCOHOLIC FERMENTATION 77 



constituting its tissues, than in the juice of the grape or 

 the must of beer where it finds everything composed of 

 utilizable elements. Nevertheless, in his Memoire sur la 

 fermentation alcoolique Pasteur succeeded in giving an 

 example of fermentation accomplished under these 

 difficult conditions. 



Later, feeling the importance of this experiment, he 

 returns to it, perfects it, and renders it surer by em- 

 ploying a more vigorous yeast than that of his first 

 experiments. It is scarcely 13 years later in his Etudes 

 sur la biere that he gives it the definitive form. But what 

 he says in his memoir of 1860 is sufficient to carry 

 conviction. 



No, it is not true, he said in substance, that there is 

 need of organic material in decomposition in order to 

 start alcoholic fermentation. An imperceptible trace 

 of yeast, introduced into a liquid containing, in addition 

 to the pure sugar, only pure crystallized mineral salts, 

 makes this sugar ferment and, at the same time, the 

 yeast develops, buds and multiplies. All the carbon 

 of the new globules is derived from the sugar, all their 

 nitrogen from the ammonia, which destroys also the 

 theory of Berzelius, according to which the ferment 

 acts only by its presence, in the same way that a red- 

 hot cannon-ball would start a fire. Moreover, it is not 

 simply in the absence of already manufactured organic 

 nitrogenous matter that the yeast globules borrow from 

 the sugar what they need : on the contrary, there is every 

 indication that this borrowing follows exactly the same 

 laws when the liquid is more favorable to fermentation. 



There is, nevertheless, a difference, namely that in 

 those rich liquids, the musts, the new globules which 

 form, finding themselves surrounded by nutrient sub- 

 stances, have no need of borrowing anything from the 

 globules already formed, while in an exhausted medium 



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