1909.] 



The Alcoholic Ferment of Yeast-juice. 



347 



concentration of the active catalytic agent, the yeast-juice would be capable 

 of bringing about the reaction with sugar in presence of phosphate at a 

 higher rate, and at the same time the optimum concentration of phosphate 

 would become greater, exactly as is observed. The question whether, as 

 suggested above, fructose actually forms part of the fermenting complex, and 

 the further questions, whether, if so, it is an essential constituent, or whether 

 it can be replaced by glucose or mannose with formation of a less active 

 complex, remain at present undecided, and cannot profitably be more fully 

 discussed until the results of experiments now in progress are available. 



It must, moreover, be remembered that different samples of yeast-juice 

 vary to a considerable extent in their relative behaviour to glucose and 

 fructose, so that the phenomena under discussion may be expected to vary 

 with the nature and past history of the yeast employed. 



Summary. 



1. Mannose behaves towards yeast-juice both in the presence and in the 

 absence of added phosphates in the same manner as glucose. 



2. Fructose resembles both glucose and mannose in its behaviour towards 

 yeast-juice, but in the presence of phosphates is much more rapidly 

 fermented than the other sugars, and the optimum concentration of phosphate 

 is much higher. 



3. Fructose has the property of inducing rapid fermentation in presence 

 of yeast-juice in solutions of glucose and mannose containing such an excess 

 of phosphate that fermentation is only proceeding very slowly. No similar 

 property is possessed by glucose or mannose. 



