208 LAURENCE F. FOSTER 



the second generation culture. Subsequent transplants do not 

 show lower levels of Ph. 



2. Plain broth cultures of Streptococcus hemolyticus show a 

 decrease in Ph which is practically the same as that exhibited by 

 cultures of the organism in sugar-free broth. This is believed to 

 be due to a selective action upon that portion of the peptone mole- 

 cule which Pick has shown reacts typically like a carbohydrate. 



3. Streptococcus hemolyticus is able to produce its characteris- 

 tic final Ph in neutral broth containing 0.2 per cent glucose. 

 Concentrations of glucose up to 1 per cent have no further 

 effect upon the level of the final Ph. 



4. The final hydrogen-ion concentration of the streptococcus 

 is not influenced by the presence of K2HPO4 in concentrations up 

 to 1 per cent providing sufficient glucose is present. 



5. Titration curves show that horse serum in broth exerts a 

 slight but distinct buffer effect. 



6. The curves of acid formation with time may be separated 

 into five characteristic periods; (1) stationary period, (2) lag 

 period, (3) maximum period, (4) period of negative acceleration, 

 and (5) maximum stationary period. 



7. Through an increase in the amount of inoculum or by 

 employing a parent culture of suitable age as a source of inoc- 

 ulum it is possible to reduce the stationary and lag periods to a 

 minimum. 



8. The presence of 5 per cent horse serum in glucose broth 

 reduces lag in acid formation by two to four hours. This may be 

 due to, (1) the presence of growth-accessory substances, or (2) 

 the presence of easily available nutritive materials. 



9. In glucose broth the maximum period of acid formation 

 is initiated usually between the sixth and the eighth hours and 

 is maintained for two hours. Maximum production of hemo- 

 toxin has been found to occur between the sixth and the eighth 

 hours. 



10. The most rapid formation of acid takes place in broth 

 adjusted to a Ph of 8.1, while a minimum of lag is shown in broth 

 of Ph 7.6. The optimum Ph for acid formation is believed to 

 lie between these two levels, or at 7.8. 



