STREPTOCOCCUS HEMOLYTICUS 



209 



11. The limits of hydrogen-ion concentration which support 

 growth of Streptococcus hemolyticus are as follows: 



12. Acidity is the chief factor contributing to inhibition and 

 death of the streptococcus in glucose broth cultures. This is 

 evidenced by the fact that growth proceeds luxuriantly in fil- 

 trates from active cultures the acidity of which has been neu- 

 tralized by a base. 



13. At a Ph of 5.25 lactic and acetic acids appear to have 

 about equal disinfecting powers for Streptococcus hemolyticus. 

 Organisms live for longer periods in filtrates from active cultures 

 than in broth brought to the same Ph with either lactic or acetic 

 acids. 



14. A marked increase in tolerance for acid is shown by 

 streptococci in the presence of horse serum. In one test it was 

 found that viabihty persisted for a period nearly four times as 

 long in serum-glucose broth of Ph 5.20 as was evident in glucose 

 broth adjusted to the same Ph. 



