ALCOHOLIC FERMENTATION OF SUGAR 143 



The fermentation of mannose and fructose in the presence 

 of yeast juice has also been examined by Harden and 

 Young. They discovered that while mannose behaves towards 

 yeast juice in the same manner as glucose both in presence 

 and absence of added phosphates, fructose is much more 

 rapidly fermented in the presence of phosphates than either 

 of the other two sugars. 



An excess of phosphates lowers the rate of fermentation 

 of glucose and mannose by yeast juice, but an addition of 

 fructose to the fermenting mixture under these conditions has 

 the effect of inducing a rapid fermentation of the other sugars. 

 Fructose in this case appears to act as a catalyst. The addition 

 of glucose or mannose under similar circumstances has no 

 similar effect. 



The precise part played by the fructose in this interesting 

 change is not yet fully elucidated. 



The fermentation produced by yeast juice is, of course, 

 not exactly the same thing as the fermentation which results 

 from the activity of the living yeast cell. The respiratory, as 

 distinct from the fermentative, activity of the yeast has also 

 to be considered. While Harden and Young's researches are 

 of the highest value as an intimate study of a detached 

 portion of the problem, the study of the conditions of activity 

 of the living cell is, of course, also necessary for a complete 

 solution of the question. 



The labours of earlier workers in this field have been 

 supplemented in recent years by the researches of Slator. 



He determined the rate of fermentation by measuring the 

 change of pressure due to evolution of carbon dioxide. 



He found that in comparatively small intervals of time the 

 rate of fermentation was proportional to the amount of yeast 

 taken, and was independent of the concentration of the sugar 

 except in very dilute solutions. 



The interesting observation was made that while galactose 

 is not fermented by yeasts grown in other solutions, it is 



