88 UNIVERSITY OF WISCONSIN STUDIES 



The fermentation of carbohydrates and alcohols. In con- 

 sidering the ability of these cultures to utilize different sources 

 of carbon some consideration must be given to the difficulty 

 sometimes encountered in determining if a fermentation has 

 actually taken place. With the ordinary culture and most 

 of the sugars and alcohols there is no difficulty in determining 

 fermentation either by the gas formation, the change in 

 titratable acidity, or in hydrogen ion concentration. With 

 some cultures the reaction is obscured by a weak evolution of 

 gas or a rapid reversion of the reaction. 



-3.0 V.and f? 1- 



F5g. 2 



In most of the sugars the change in reaction is rapid and 

 distinct but in some of the alcohols, notably glycerol, the 

 fermentation is so slow that it may be in doubt for many 

 days. We have considered an evolution of gas in the absence 

 of any apparent change in acidity or an appreciable change 

 in acidity without evident gas formation as fermentations. 

 Figure 2 shows that while there is no perfect correlation, 

 there is a distinct difference in the fermentative ability of the 

 two groups. The cultures of the high ratio group almost 

 without exception ferment saccharose and raffinose while only 

 about 40 per cent of the low ratio group utilize these sugars. 

 Starch is also utilized much more commonly by the high ratio 

 cultures. On the other hand, more of the low ratio cultures 

 ferment the alcohols mannitol, glycerol and dulcitol than is 

 the case with the high ratio group. This does not hold for 

 adonitol which seems to be more available for the high ratio 

 type. The percentage of cultures fermenting the glucoside 



