IDENTITY OF THE LACTIC-ACID SLREPTOCOCCUS 171 



These tests, it is thought, are of sufficient value to make 

 possible the separation of these two groups of streptococci, but 

 it would be advantageous further to limit the number of tests 

 and to establish the most constant ones. The differences in 

 the groups relative to chain formation and action on milk are, 

 in all probability, significant, but for reasons given earlier in 

 this paper, it is not desirable to emphasize them greatly. The 

 remaining characteristics, however, we believe to be stable ones 

 — as stability occurs in the physiological characters of bacteria. 

 Among the dyes neutral red did not give an absolute differentia- 

 tion of the cultures studied and so might be eliminated in favor 

 of methylene blue. As the action on indigo carmine was identi- 

 cal in all cases with that on litmus, it also might be discarded. 

 The five remaining tests we wish especially to recommend as 

 furnishing a ready and simple means of separating the milk 

 streptococci. Growth at 10°C., reduction of methylene blue 

 in milk, and the reduction of litmus (or indigo carmine) in milk 

 previous to curdling are characters which have divided per- 

 fectly, in our study, the two types; Strept. lacticus having in all 

 cases reacted positively while the Strept. pyogenes cultures, with- 

 out exception, failed so to act. Absolute differentiation was not 

 obtained with the other two tests — growth at 43°C. and the 

 fermentation of sucrose — but the Strept. pyogenes type, in the 

 great majority of cases, gave positive reactions whereas the 

 lactic-acid streptococci in both instances were usually negative. 



Although the object of this work was only to establish points 

 of difference between the two groups of organisms, it should, 

 aside from its main purpose, be of value m helping to define 

 more clearly the characteristics of the Strept. lacticus (Bad. 

 lactis-acidi) group of bacteria. As was pointed out previously, 

 our results do not substantiate some of the generally accepted 

 ideas concerning its fermentative properties. The facts estab- 

 lished with reference to its temperature requirements and reduc- 

 ing ability, should so identify the true lactic-acid organism as to 

 enable more reliable work than has been possible in the 

 past concerning morphology, physiology, natural habitat and 

 pathogenicity. 



