196 



LAURENCE F. FOSTER 



Experiment XI. The relation of initial hydrogen-ion concentration 

 of broth to the growth of Streptococcus hemolyticus^ 



Portions of infusion broth were adjusted to values ranging 

 from Ph 5.0 to 9.0 and after the addition of proper amounts of 

 glucose and horse serum, were incubated for twenty-four hours 

 to insure sterility. Each tube contained 5 cc. of medium. The 

 following series were used: (1) Plain broth, (2) 1 per cent glucose 

 broth, (3) 1 per cent glucose-5 per cent horse serum broth. 

 The inoculum consisted of 0.2 cc. of an eighteen-hour culture in 

 1 per cent glucose broth. Duplicate uninoculated tubes were 

 carried as controls. The results are found in table 10. 



The following summary will perhaps serve better to express 

 the outstanding points of this experiment : 



Minimum Ph permitting growth 



Maximum Ph permitting growth 



Ph limits within which luxuriant growth occurs 



PLAIN 

 BROTH 



6.35 

 8.50+ 

 6.60 

 8.50 



1 PERCENT 

 GLUCOSE- 

 BROTH 



6.35 

 8.50+ 

 6.35 

 8.50 



1 PER CENT 

 GLUCOSE, 

 5 PER CENT 

 SERUM- 

 BROTH 



5.70 

 9.25+ 

 5.90 

 9.25 



Whereas the limits of reaction which permit growth appear 

 to be the same in plain and in 1 per cent glucose broth, the 

 presence of horse serum in addition to the glucose enables the 

 organisms to tolerate greater degrees of acidity and alkalinity. 

 Hence it is to be emphasized that in expressing the levels of 

 hydrogen-ion concentration which limit the growth of organisms 

 the exact composition of the experimental media must be men- 

 tioned. It has been noted previously that horse serum exerts a 

 strong stimulatory effect upon the growth and fermentative 

 activities of the streptococcus. Here we find additional evidence 

 of such an action in an increased tolerance of the organisms for 

 acidity and alkalinity, manifested by growth throughout a wider 

 range of hydrogen-ion concentration. 



From the results of experiment VIII it must be concluded that 

 the optimum Ph, based upon the rate of acid formation in 1 



