STREPTOCOCCUS HEMOLYTICUS 169 



alkaline phase had been initiated through the splitting of pep- 

 tone. The presence of buffer, according to Kligler, keeps the 

 hydrogen-ion concentration below the lethal point and thus 

 allows the organism to continue its activity over a longer period. 

 As a result of this regulatory power the amount of glucose which 

 may be used will vary, within limits, with the relative amount 

 of buffer material present. Bronfenbtenner and Schlesinger 

 (1918) working with Bad. coli have tried similar experiments by 

 noting the effects of varying amounts of lactose, peptone, and 

 buffer salts upon gas formation and final Ph. After trying some 

 294 combinations, these investigators concluded that with any 

 given concentration of carbohydrate the amount of free acid 

 depends upon the concentration of buffer in the medium. As 

 the amount of peptone increases, the per cent of sugar attacked 

 is smaller and lower hydrogen-ion concentrations result. The 

 necessity of carefully controlling the composition of media 

 employed in fermentation experiments is emphasized. 



From the foregoing review the following facts seem to have 

 been well established: 



1. In any given medium a definite concentration of sugar 

 must be present if the organism in question is to produce its 

 characteristic final hydrogen-ion concentration. 



2. This minimum concentration of sugar will depend upon the 

 concentration of buffer salts present, as well as upon the concen- 

 tration of peptone in the medium. 



3. In mal-dng estimations of this minimum concentration of 

 sugar required for the production of the final hydrogen-ion con- 

 centration the quantity of buffer should be known as well as the 

 initial Ph of the culture medium. 



4. With increasing concentrations of buffer salts there is an 

 increased neutralizing power which delays the production of the 

 final acidity level, thus allowing the organism more time for 

 fermentation. 



