188 



LAUEENCE F. FOSTER 



Experiment IX. The relationship between the rates of acid forma- 

 tion and growth of Streptococcus hemolyticus in glucose 

 broth and in glucose-serum broth 



Forty cubic centimeter portions of 1 per cent glucose broth 

 and 1 per cent glucose-5 per cent horse-serum broth were pre- 

 pared and incubated to insure sterility. Inoculations were 

 made from an eighteen-hour, second-generation culture in 1 

 per cent glucose broth into the two lots of media. Ph deter- 

 minations and plating of dilutions were carried out every two 

 hours. The experiment continued through twelve hours. 



Technic of plating. 1.8 cc. of plain broth were used as dilut- 

 ing fluid throughout. 0.2 cc. of culture was transferred into 

 this amount of broth and the fluids mixed by carefully drawing 

 up and down in the pipette, after which 0.2 cc. of this dilution 

 were added to 1.8 cc. of broth, etc. until all the dilutions required 

 had been made. Especial care was taken to avoid agitation of 

 the material during the preparation of the dilutions. Nutrient 

 agar containing 10 per cent of defibrinated rabbit's blood was 

 used as a plating medium. 



Table 7 contains the results of the experiment. 



TABLE 7 

 Experiment IX 



* Counts are expressed in millions per cubic millimeter. 



Attempts to construct growth curves by plotting the loga- 

 rithms of counts against time brought out certain irregularities 

 which made impossible the formation of smooth curves. Con- 



