172 J. M. SHERMAN AND W. R. ALBUS 



SUMMARY 



A study was made of 100 cultures of organisms isolated from 

 milk. The collection was so made that 50 of these cultures, it is 

 believed, represented the true lactic-acid streptococcus and the 

 other 50, streptococci of the pyogenes type. 



Morphological observations were made from agar, broth and 

 bile. The tendency to form chains on agar and on broth was 

 not so marked among the cultures of the Strept. lacticus group 

 as among the organisms of the Strept. pyogenes type. On lac- 

 tose-peptone-bile, however, the Strept. lacticus cultures grew 

 readily and formed long, typical streptococcic chains. 



Among the cultures studied, the representatives of the Strept. 

 lacticus type as a class had a more vigorous action on milk than 

 did the other streptococci; coagulation was usually more prompt 

 and larger amounts of acid were formed. 



The fermentative characteristics of the two groups were 

 quite similar with all of the substances used except sucrose. 

 This compound was attacked by 38 of the 50 cultures of the 

 pyogenic streptococci, while all but three of the lactic-acid 

 streptococci failed to ferment it. 



At 10°C. all cultures of the lactic-acid bacteria grew while 

 none of the cultures of the Strept. pyogenes type were able to 

 develop at this temperature. At 43°C. only 3 of the lactic 

 organisms grew, whereas the pyogenic streptococci developed in 

 84 per cent of the cases. 



The reduction of stains proved a valuable means of distin- 

 guishing these groups. With methylene blue all of the lactic 

 streptococci caused reduction, while all of the pyogenic strepto- 

 cocci failed to reduce. Litmus and indigo carmine in milk were 

 completely reduced before curdling by all of the Strept. lacticus 

 cultures; the cultures of Strept. pyogenes caused no decoloriza- 

 tion of these compounds previous to curdling, and the reduction 

 after coagulation was slow and never absolutely complete. 

 Neutral red, though of value, did not give as perfect a differen- 

 tiation between the two types as did the other dyes. 



