192 MICROBIOLOGY 



20 degrees, and ferments saccharose and the glucosides (sali- 

 cin and coniferin), but not lactose, raffinose, inulin, or man- 

 nite. It fails to clot milk or to reduce neutral red. 



2. Streptococcus mitis. This type is found most com- 

 monly in human saliva and feces, but it is not as a rule asso- 

 ciated with disease. It is short-chained, grows well on gelatin 

 at 20 degrees, and acidifies milk without clotting. It ferments 

 lactose as well as saccharose and salicin, but gives a negative 

 reaction to the other tests. 



3. Streptococcus pyogenes. This type represents the 

 highest parasitic development of the group, being rarely found 

 except in association with definite pathological conditions. It 

 occurs in long chains, usually growing in woolly masses at the 

 bottom of a clear broth. It grows well on gelatin at 20 degrees. 

 It is actively hemolytic, but does not form hydrogen sulphide 

 in broth cultures. It strongly acidifies milk, but never clots 

 it, nor does it reduce neutral red. The usual positive reac- 

 tions with Gordon's tests are saccharose, lactose, and salicin, 

 It is highly pathogenic for animals. 



4. Streptococcus salivarius. This type is the commonest 

 form in the mouth, although it is also found elsewhere. It is 

 a short-chained form which usually renders broth uniformly 

 turbid. Its growth on gelatin at 20 degrees is variable. It 

 clots milk and reduces neutral red and ferments saccharose, 

 lactose, and raffinose. 



5. Streptococcus anginosus. This type is a pathogenic 

 long- chained form, allied in other respects to Str. salivarius, 

 and bearing to it much the same relation which Str. pyogenes 

 bears to Str. mitis. It occurs most commonly in cases of scar- 

 latina and other forms of sore throat. It is long-chained and 

 produces a flocculent deposit in broth. It generally fails to 

 grow on gelatin at 20 degrees, and is markedly hemolytic. 

 Like Str. salivarius, on the other hand, it clots milk, reduces 

 neutral red, and forms acid in saccharose, lactose and raffinose. 



6. Streptococcus faecalis. This type is specially charac- 

 teristic of the human intestine. It is short-chained and ren- 

 ders broth uniformly turbid. It grows readily at 20 degrees 



