ALCOHOLIC FERMENTATION OF SUGAR BY YEAST. 591 



ditions for the fermentative agents. Towards the end 

 of the fermentation these materials seem to accumulate, 

 and those fermentative agents which are only able to set 

 up the fermentation with difficulty, and which in reality 

 require other conditions of existence, furnish bye-pro- 

 ducts in especially large quantities; for example, Mucor 

 inucedo furnishes more than Mucor racemosus, and 

 Mucor stolonifer more than Mucor mucedo. 



We may, perhaps, suppose that in succinic acid, Significance 

 glycerine, &c., we have represented the special products products. 

 of the tissue change of the yeast. As a matter of fact 

 we must assume that, in addition to the splitting up of 

 the sugar, there also occur decompositions, and, where 

 oxygen is present, oxidations of the complex molecules 

 of the protoplasm of the yeast, which are composed of 

 nitrogenous and non-nitrogenous groups of atoms ; as a 

 consequence the ordinary products of the destructive 

 tissue change appear in the nutrient mixture. It 

 is, however, difficult to identify these products with 

 those bye -products which appear in fermentation ; the 

 quantity of the latter is much too great, and their 

 quality also is too peculiar. Further, in this case, tbe 

 amount of the bye-products must be proportional to the 

 amount of the active yeast cells which are present, and 

 must also, in the first place, depend on the quantity 

 which has been sown. But as yet nothing has been 

 observed as regards any such relation. We must there- 

 fore either assume that the decomposition of the sugar in 

 the fermentative action in reality occurs, at any rate as 

 regards the largest amount, according to a more com- 

 plicated formula, in which there is a constant formation 

 of glycerine and succinic acid ; or that the appearance 

 of these bye-products is caused by impure fermentescible 

 material, by the admixture of bacteria, and by their 

 decomposition of the nutrient materials. The possi- 

 bility of such impurities must be admitted in the case 

 of the experiments which have been as yet made, in 

 spite of the great precautions which have been taken 

 by various authors since the time of Pasteur, because it 

 was not possible, in the earlier methods, to isolate pure 



