204 



LAUKENCE F. FOSTER 



interesting that they will be presented in this section of the 

 paper. 



In numerous experiments it has been observed that a glucose 

 broth culture of Streptococcus hemolyticus, after reaching a sta- 

 tionary level of hydrogen-ion concentration during the first 

 twenty-four hours, remains viable for a period varying from two 

 to five days. Subcultures made on each succeeding day during 

 this period of death show stationary and lag periods of increasing 

 duration. To gain some idea of the factors contributing to this 

 inhibition the following experiments were carried out: 



Experiment XII . The growth and acid production of Streptococcus 

 hemolyticus in neutralized filtrates 



A transplant of the usual quantity of an eighteen-hour culture 

 was made into 1 per cent glucose broth, Ph 7.5, and the material 

 incubated until sterile (five days). The culture was then filtered 

 through a sterile Berkefeld candle, after which the filtrate was 

 brought back to the original reaction with sterile NaOH and 

 re-inoculated with a fresh, actively growing culture. This 

 procedure was repeated until no further growth resulted upon 

 inoculation. The results are found in table 11. 



TABLE 11 



Experiment XII 



From the data shown in table 11, it would appear that acidity 

 is the chief factor causing inhibition and death of the strepto- 

 coccus in glucose broth cultures. The inhibition which finally 

 appears may be due to two factors; first, to an exhaustion of 

 nutrient materials in the medium, and second to the accumula- 

 tion of toxic products other than acid which check metabolism 

 and growth. 



