168 



J. M. SHERMAN AND W. R. ALBUS 



As may be seen from table 5 the reduction of dyes proved 

 to be an efficient test to differentiate between these two groups 

 of bacteria. Methylene blue differentiated the groups per- 

 fectly, all of the true lactics causing a complete reduction of the 

 stain within twenty-four hours and previous to curdling, while 

 the udder streptococci failed entirely to cause reduction. After 

 six days the tubes containing the latter class were not curdled 

 and there was no evidence that growth had taken place. Some 

 of these cultures were transferred to plain milk tubes but no 

 growth occurred, thus indicating that not only were they unable 



TABLE 5 

 Reduction of dyes 



Methylene blue 



Methylene blue (within twenty-four hours) 



Methylene blue (before curdling) 



Litmus 



Litmus (within twenty-four hours) 



Litmus (before curdling) 



Indigo carmine 



Indigo carmine (within twenty-four hours) . 



Indigo carmine (before curdling) 



Neutral red 



Neutral red (within twenty-four hours) 



Neutral red (before curdling) 



CULTURES 

 1 TO 50 



per cent positive 



100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 



92 



84 

 4 



CULTURES 

 51 TO 100 



per cent p isitive 













 100* 









 100* 























* Reduction not complete. 



to reduce methylene blue, but that, in the concentration used, 

 it had entirely inhibited growth and led to their destruction. 

 The longest time required for any of the lactic-acid streptococci 

 to reduce was ten hours, while a large majority caused a com- 

 plete decolorization within eight hours after inoculation. 



The actions on litmus and indigo carmine were apparently 

 identical. In both cases the lactic-acid streptococci caused a 

 prompt reduction; with litmus the longest time taken was 

 eleven hours, while with indigo carmine thirteen and one-half 

 hours was the longest time required. The udder cultures, on 



