STREPTOCOCCUS HEMOLYTICUS 165 



sistently within the first twenty-four hours following incubation, 

 nevertheless in this experiment it was decided to allow a forty- 

 eight-hour incubation period before making Ph determinations 

 to insure the completion of the fermentation. 



Reference to table 1 shows that of the several groups of sub- 

 stances tried only the hexoses and disaccharides were fermented 

 by the streptococcus. A wide variation in final Ph is noted. 

 No explanation of these differences is attempted at the present 

 time. Clark (1915b) working with Bact. coli, reports lower 

 Ph levels in glucose broth than in lactose broth, while Jones (1920) 

 has described a similar phenomenon in cultures of Streptococcus 

 hemolyticus and pneumococci. Similar results are evident in the 

 present experiment. An interesting fact brought out is that 

 plain broth shows an increase in hydrogen-ion concentration. 

 It is also to be noted that in no case in which fermentation did 

 occur was the characteristic final Ph reached in the first genera- 

 tion. This would seem to indicate that in procedures for differ- 

 entiation based upon final Ph levels, several transfers of the cul- 

 tures should be made upon the same medium before conclusions 

 as to the final hydrogen-ion concentration are drawn. In nearly 

 all cases the characteristic final value was reached after one 

 transfer. 



The fact that plain broth shows an increase in hydrogen-ion 

 concentration when inoculated with the streptococcus would 

 seem to indicate that sufficient muscle sugar is present to permit 

 fermentation to the Ph level indicated. To decide this point, 

 a lot of infusion broth was inoculated with Bact. coli to ferment 

 out any free sugar, after which it was filtered, adjusted, and 

 sterilized. Upon inoculation with a culture of Streptococcus 

 hemolyticus it was found that the final Ph was the same as that 

 noted in the experiment just described. In this case the initial 

 Ph of the broth was slightly lower, namely, 7.35. A similar 

 result was experienced when sugar-free, bacto-beef broth was 

 tried. In their studies of the metabolism of Streptococcus pyo- 

 genes and other organisms Kendall and his associates (1912c, 

 1912a) found increases in titratable acidity in plain broth cul- 

 tures but carried out no determinations of hydrogen-ion concen- 



