160 



J. M. SHERMAX AXD W. R. ALBUS 



at this temperature would not be so high as if a lower incubation 

 temperature were used, but for comparing the two classes of 

 organisms it should serve the purpose. By this test it was found 

 that the lactic-acid type of streptococci (cultures 1 to 50) as a 

 group produced considerably larger amounts of acid in milk 

 than the udder cultures. If an arbitrary standard of 0.75 per 

 cent lactic acid is taken (table 2) it will be seen that the two 

 groups are divided quite well by the acid producing powers of 



to 



50 



40 



30 



20 



.55 .60 .65 7Q .7"5 .80 .65 .SO .95 



PER CENT OF LACTIC ACID. 



Fig. 1. Frequency Curve Showixg Acid Production in Milk 



their members. The difference in acid production is better 

 shown by the frequency curves presented in figure 1. 



These curves show a marked difference in the modes of the 

 two groups as to acid production in milk. The same thing is 

 true with respect to acid formation in lactose-peptone-bile. As 

 was noted before, the lactic cultures appeared to grow more 

 vigorously in bile than did the other streptococci, and the dif- 

 ference in the amounts of acid formed by the two types in this 

 medium gave further evidence of that fact. 



