166 J. M. SHERMAN AND W, R. ALBUS 



(1913) have shown that streptococci from milk are, as a rule, 

 more active at 20°C. than those isolated from the hmnan throat. 

 Experiments at low temperatures of incubation were con- 

 ducted, by inoculating litmus milk with the cultures and incu- 

 bating at the desired temperature. Growth was determined by 

 the presence or absence of visible changes in litmus milk. At 

 10°C. the two groups were differentiated perfectly; all of the 

 cultures numbered from 1 to 50, which were supposed to repre- 

 sent the Strept. lacticus type, grew, while none of the group 

 representing the Strept. pyogenes type did. The latter showed 

 no change in the litmus milk after six weeks, but when put in a 

 37°C. incubator at the end of this period the tubes all turned 

 acid, thus indicating that the cultures were alive but their 



growth had been inhibited. The lactic streptococci all showed 

 visible signs of growth within one week at 10°C. 



Tests similar to the above were also made with high tempera- 

 tures of incubation. At 43°C. was found a temperature which 

 separated the two groups quite well, but the separation was not 

 so perfect as at 10°C. In this case it was the pyogenic type 

 which grew and the lactic type which failed to grow. 



REDUCTION OF DYES 



The use of stains as an aid in the identification of bacterial 

 groups is not uncommon. Some familiar examples are the 

 employment of neutral red, fuchsin and brilliant green for 

 differentiating members of the colon-typhoid greup of organisms. 

 The reduction of neutral red was one of the characters advocated 

 by Gordon (1905) as being of value in the separation of strep- 



