STREPTOCOCCUS HEMOLYTICUS 193 



minimum in the sub-culture and growth and acid production at 

 a maximum rate are initiated early. This point is of consider- 

 able importance, though seemingly it has been overlooked by 

 many workers. 



4. The presence of 5 per cent horse serum reduces lag by from 

 two to four hours. This is correlated with an earlier period of 

 multiplication of organisms at a maximum rate. Two possible 

 explanations of this phenomenon present themselves: (1) Nutri- 

 tive materials in some easily available form may be furnished by 

 the serum or, (2) growth-accessory substances (vitamines) may 

 be present in the enriching fluid. The second possibiUty would 

 be in accord with Kligler's finding (1919) that the presence of 

 tissue extracts shortened lag in the growth of Streptococcus hemo- 

 lyticus and other organisms. Ordinarily these accessory sub- 

 stances are furnished by disintegrating cells which accounts for 

 the fact that massive inocula give better cultures than light 

 inocula. 



5. Entire absence of lag in acid formation has never been 

 noted. One case has been reported above in which a two-hour 

 lag was apparent in glucose-serum broth. 



6. In glucose broth the maximum period is initiated between 

 the sixth and eighth hour and is usually maintained for two 

 hours after which the period of negative acceleration sets in. 

 The Pii decrease per hour in this medium is 0.42 (average of 

 four experiments) . In glucose-serum broth the maximum 

 periods sets in two to four hours earlier and proceeds for two 

 hours. The Ph decrease per hour during this period is 0.50. 



Recent work in this laboratory by Dr. Marjorie W. Cook has 

 demonstrated that hemotoxin production by the ''H" strain of 

 Streptococcus hemolyticus occurs nearly always between the 

 sixth and eighth hours. It is a fact of interest that this property 

 appears during the interval which is most frequently associated 

 with maximum acid formation. 



7. In glucose broth of initial Ph ranging from 7.10 to 7.65 the 

 maximum period sets in when the Ph of the culture has been 

 brought to 6.45-6.80. The relation of this level of acidity to 

 the optimum Ph of the enzymes associated with acid production 

 might be suggested as a possible explanation of this phenomenon. 



