IDENTITY OF THE LACTIC-ACID STREPTOCOCCUS 169 



the other hand, caused a reduction but it did not take place 

 until after two or more days and then it was never absolutely- 

 complete. The important distinction, however, is that the 

 reduction in the lactic cultures took place previous to curdling, 

 whereas the pyogenic streptococci caused no reduction until 

 after coagulation. This we believe represents a fundamental 

 physiological difference between the two groups and it is to be 

 considered, therefore, of value as a differential test. Since the 

 litmus, indigo carmine, methylene blue and low temperature 

 tests are all perfectly correlated, it would appear that the 

 method of distinguishing between lactic-acid organisms and 

 other milk streptococci based upon whether they cause reduc- 

 tion in litmus milk before curdling is sound. 



Neutral red,, which has been used considerably in studying 

 streptococci, proved the least valuable of the four stains 

 employed. Though the two groups were separated quite well, 

 the distinction based upon this dye was not a perfect one. The 

 lactic-acid organism did not cause as prompt reduction with 

 neutral red as with the other stains, it requiring from twelve to 

 fifty hours to decolorize this compound; and the reduction took 

 place in most cases after curdling. Only four of the lactic 

 cultures failed to reduce while all of the other streptococci gave 

 negative reactions. 



DISCUSSION 



From the data which have been presented, it seems justifi- 

 able to conclude that the organisms studied represent two classes 

 of streptococci; cultures numbered 1 to 50 the true lactic-acid 

 streptococcus, and the other group (cultures 51 to 100) the pyo- 

 genic type. A review of the tests made will show a number of 

 characters which differentiate the cultures into those two main 

 types. The diagram given in figure 4 shows very clearly some 

 of the fundamental differences between these groups. In this 

 graph are presented only those tests which appeared to be of 

 considerable differential value, those showing only slight differ- 

 ences between the two types being omitted. 



