HEMOLYTIC STAPHYLOCOCCI 



15 



ship between hemolysis and acid production. In view of the methyl 

 red test of differentiation of B. coli and B. aerogenes by this medium, 

 it seemed at the time that it might possess some value in this work. 

 The peptone medium contained 0.5% K 2 HPO 4 , 0.5 peptone (Difco), 

 and 0.5% dextrose, and was adjusted to PH 7.4. 



Table 6 shows the H-ion readings of the different cultures from time 

 to time as specified. With the exception of Al, all strains reach an 

 end-point of P H 4.2-4.6 within 96 hours. Although there seem to be 

 differences in the earlier readings, there is no line of demarcation 

 between the acid production of the cultures. These differences are 

 probably explainable on differences in numbers inoculated, periods of 

 lag, etc. 



TABLE 6 



ACID PRODUCTION IN CLARK AND LUBS MEDIUM * 



* Figures represent -values of H-ion concentration. 



At this point, the question arose as to what determined the acid 

 end-point of the cultures. To approach an answer, 2 experiments were 

 planned : ( 1 ) Cultures were grown in the same medium with the reac- 

 tion adjusted to P H 4.4; (2) cultures which had already reached an 

 acidity of P H 4.4 were killed by heating at 56 C. for 30 minutes and 

 inoculated with a 24-hour culture. 



In both these cases, the H-ion concentration 'was increased to 4.2 

 and 4 after 24 hours. It might be of interest to quote here the work 

 of Hall and Frazer 29 who found that staphylococci could reach a H-ion 

 concentration of 2.6 an end-point which exhibited no relation to sapro- 

 phytic or pathogenic forms. 



29 Abstract, Lancet, 1921, 18, p. 912. 



