192 



LAURENCE F. FOSTER 



(6) began its acid formation after two hours at a slow, rather 

 constant rate but at the close of the experiment had only reached 

 a Ph of 7.0. After thirty hours its Ph was 6.0. It was not 

 known whether this culture ever reached the final characteristic 

 hydrogen-ion concentration. Culture (1) showed no growth 

 while (2) was found to grow very poorly, the Ph after thirty 

 hours being at the same level as at the fourteen-hour period. 



VI 



VII 



VIII 



IX 



6.45-5.70 

 6.70-5.85 

 6.60-5.70 

 6.80-5.90 



0.34 

 0.425 

 0.45 

 0.45 



Medium: 1 per cent glucose, 5 per cent horse serum broth 



i 



From the foregoing data the following conclusions regarding 

 the rate of acid formation in cultures of Streptococcus hemolyticiis 

 may be drawn: 



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

 into five characteristic periods: (1) Stationary period, (2) lag 

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

 (5) maximum stationary period. 



2. It is possible to reduce the duration of the stationary and 

 lag periods to a minimum through increasing the quantity of 

 inoculum. Whether this holds beyond a certain point is not 

 known. 



3. The age of the culture that is serving as a source of inocu- 

 lum may exert a decided effect upon the duration of the station- 

 ary and lag periods in the sub-culture. If the inoculum be taken 

 from a culture during its maximum period, lag is reduced to a 



