HYDROGEN IONS, ETC., OF BACTERIOLOGICAL MEDIA 563 



of low buffer index, Bacto bouillon and Liebig extract bouillon, 

 were inoculated with the mixed culture from bouillon C3, in- 

 cubated forty-eight hours with sterile controls of the same media, 

 and the buffer indices titrated. The results, tabulated in table 

 2, show that in Bacto bouillon the index was doubled and in 

 extract bouillon was increased slightly. Cultures of Bact. coli 

 in the same media showed small increases in the indices of both, 

 A clear centrifugate of the mixed culture in Bacto bouillon had 



TABLE 2 

 The effect of cultures on the buffer index 



practically the same buffer index as the clouded culture, showing 

 that the increase was not due to the presence of bacterial bodies 

 but to substances in solution. A similar experiment was con- 

 ducted with Bact. alkaligenes using fermented bouillon and 

 plain unfermented veal infusion bouillon. There was an appre- 

 ciable increase in the buffer index of the culture in fermented 

 bouillon but only a slight increase in that of the plain bouillon. 

 In other experiments the buffer indices of cultures of Bact. coli 

 in plain veal bouillon increased markedly, but when an. excess 

 of glucose was added little or no change in the buffer index 



