564 



J. HOWARD BROWN 



occurred. A hemolytic streptococcus produced no change in 

 the buffer index of glucose bouillon though the hydrogen 

 ion concentration increased from pH 7.1 to pH 4.7 during incu- 

 bation for eight days. The results of these experiments sug- 

 gest that in the cases mentioned the increase in buffer index was 

 the result of protein metabolism. It is suggested that the ability 

 or failure of a culture to produce changes in the buffer indices 

 of media may be of differential value. 



TABLE 3 



Influence of the reserve alkalinity and the amount of fermentable sugar on the final 

 hydrogen ion concentration 



In figure 1 are plotted the buffer indices of a number of bouil- 

 lons. The pH values are located along the ordinate axis and 

 the percentage of normal acid or alkali used on the abscissa. 

 By the simple methods of titration described above three points 

 are located, the initial pH at A (as shown on the curve of fermented 

 bouillon A9), pH 8.0 at B, and pH 5.0 at C. If other points 

 between A and C are determined they are found to lie very close 

 to the straight line from A to C. The true form of the curve for 

 fermented bouillon A9 is shown. A comparison of the curves 

 shown in figure 1 shows that the smaller the buffer index the 

 more nearly does the curve approach a straight line. 



