70 BIOLOGY OF PNEUMOCOCCUS 



enzymes have been demonstrated for these reactions. In addition 

 to glucose, galactose and levulose are actively fermented with the 

 formation of lactic acid, as well as the trisaccharide, trehalose, 

 and the glucoside, salicin. The fermentation of alcohols is much 

 less marked. Slow acid production takes place in media containing 

 glycol, glycerol, and erythritol; some strains slowly produce acid 

 from mannitol, but there is no action on dulcitol or sorbitol. The 

 pentoses, arabinose and xylose, are slowly attacked (Mair 552 ). Zo- 

 zaya 1586 added levan, obtained from B. mesentericus and B. sub- 

 tilis, to the list of substances fermentable by Pneumococcus. Dex- 

 tran, obtained from Leuconostoc mesenteroides was not affected. 

 Although the change in levan was less than that in inulin, the 

 acidity in both cases seemed to be mainly due to lactic acid. 



Acid Production 



Supplementing the brief mention that has already been made of 

 the formation of acid from saccharides by Pneumococcus, some of 

 the factors that condition that reaction are as follows: The 

 amount of sugar present in the medium determines the degree of 

 acidity attained. If sufficient carbohydrate is present, growth 

 ceases at an acid reaction of pH 5.0. If there is less than 0.4 per 

 cent of sugar, growth ceases at a lower hydrogen ion concentra- 

 tion, apparently because of exhaustion of carbohydrate. If no 

 carbohydrate is present save that extracted from the meat from 

 which the broth is made, growth initiated at pH 7.8 ceases at 

 about pH 7.0. If the reaction of bacteria-free filtrates of plain 

 broth cultures in which growth has ceased is readjusted to pH 7.8 

 and the medium reinoculated with Pneumococcus, no growth oc- 

 curs unless carbohydrate is added. However, if bacteria-free fil- 

 trates of dextrose-broth cultures in which growth has ceased are 

 readjusted to pH 7.8 and reinoculated with Pneumococcus, growth 

 is resumed. Cultures of Pneumococcus, with maltose, saccharose, 

 lactose, galactose, raffinose, dextrose, and inulin give identical re- 

 sults in the rate of reaction change and the final hydrogen ion 



