164 LAURENCE F. FOSTER 



recognized fact that the pathogenic streptococci develop more 

 luxuriant growth upon this medium than upon broth prepared 

 from beef extract. In some of the experiments "Bacto-beef" 

 (Digestive Ferments Company) was employed instead of beef 

 juice as a base. Growth upon this medium was found to be as 

 luxuriant as upon the usual beef infusion broth. The broth 

 contained 1 per cent peptone (Difco or Parke, Davis, and Com- 

 pany), and 0.5 per cent NaCl. Adjustment to the desired Ph 

 was made according to the method previously described. The 

 limits of Ph, 7.0-7.6, were found to favor luxuriant growth of the 

 organism. The prepared broth was always incubated for 

 twenty-four hours previous to inoculation to insure its sterihty. 

 Ph determinations.^ These were made by the method described 

 in a former paper using 1 cc. of culture plus 4 cc. of freshly boiled 

 and cooled distilled water. A tube containing the same mate- 

 rials without indicator was always used by the method of super- 

 position to eliminate as far as possible factors of color and 

 turbidity. Determinations carried out in this way permitted 

 readings to within 0.05 Ph in nearly all cases. 



Experiment I. The final hydrogen-ion concentration of Strepto- 

 coccus hemolyticus in broth containing various fermentable 

 substances commonly employed in the bacteriological laboratory; 

 also an attempt to investigate the possibility of an experimental 

 adaptation to a given sugar medium, through repeated transplan- 

 tation. 



Inoculation of 0.4 cc. of an eighteen-hour, second-generation 

 culture was made into 10 cc. lots of beef infusion broth contain- 

 ing the given fermentable material in 1 per cent concentration. 

 Transplants from each tube were made, into sterile lots of 

 media of corresponding composition after twenty-four hours 

 incubation. In this manner five generations were carried. 

 Although the "H" strain had previously been found to produce 

 the characteristic final hydrogen-ion concentration quite con- 



' The symbol Ph of Sorensen is used throughout to designate the hydrogen 

 ion concentration. 



