STREPTOCOCCUS HEMOLYTICUS 167 



stance reacting typically like a carbohydrate. Although the 

 peptone used in the present experiments was not Witte's it 

 seems entirely possible that American peptones such as the one 

 used here (Parke, Davis and Company) might contain a similar 

 carbohydrate substance. The fact that a definite increase in 

 hydrogen-ion concentration has always been observed in the 

 sugar-free broth employed surely would lend support to such a 

 supposition. 



II. THE INFLUENCE OF VARYING AMOUNTS OF GLUCOSE AND BUFFER 



SALTS UPON THE FINAL HYDROGEN-ION CONCENTRATION 



OF STREPTOCOCCUS HEMOLYTICUS 



It has long been recognized that the acidity produced by cer- 

 tain organisms in culture media results from the elaboration of 

 acid substances through a fermentation of material, mainly of 

 carbohydrate nature. With the introduction of accurate meth- 

 ods of evaluating the acidity produced in bacterial fermentations 

 through a determination of the concentration of the hydrogen- 

 ions, it became necessary to investigate the factors which may be 

 operative in the production of a limiting or final hydrogen-ion 

 concentration. Thus, Clark and Lubs (1915) in their work on 

 the differentiation of the bacteria of the colon-aerogenes family, 

 used media containing amounts of glucose varying from to 0.5 

 per cent and demonstrated that by increasing the concentration 

 of the sugar up to a certain point a greater final acidity resulted. 

 If sufficient sugar was present for the limiting acidity to be pro- 

 duced, no alkaline reversion occurred in their cultures. Browne 

 (1914), using cultures of Bad. coli in lactose-broth, found that 

 acid production was less marked in media containing under 1 

 per cent sugar but that the use of amounts over 1 per cent resulted 

 in no increase. Browne titrated his cultures with n/20 NaOH 

 but failed to make determinations of the final hydrogen-ion con- 

 centration. Avery and CuUen (1919b) found that pneumococci 

 were able to reduce the Ph of glucose-broth from 7.50 to 5.10 

 provided 0.4 per cent of the sugar was present. Increasing 

 concentrations of glucose up to 4 per cent showed no change in 



JOURNAL OF B.VCTF.RIOLOGY, VOL. VI, XO. 2 



