312 AGEICXJLTUBAL AND INDUSTRIAL BACTERIOLOGY 



auction or pathogenicity need not be emphasized here. It 

 may be noted that Streptococcus pyogenes is morpho- 

 logically very much like the Streptococcus lacticus usually 

 associated with the souring of milk. 



Morphologfy. — Streptococcus pyogenes is a coccus about 

 one micron in diameter, practically always occurring in 

 chains, sometimes short and sometimes long. It is non- 

 motile, does not produce spores, is easily stained and is 

 Gram-positive. Some types produce capsules, although 

 most of the more highly pathogenic forms are capsule-free. 



Distribution. — Nonvirulent strains of Streptococcus 

 pyogenes are quite common upon the surface of the skin 

 and particularly in the mouth and on the mucous mem- 

 brane. Virulent strains have been isolated from a great 

 variety of inflammatory conditions. 



Culture. — This organism grows fairly readily upon most 

 of the ordinary culture media but not particularly 

 luxuriantly. An agar slant culture, for example, develops 

 in the form of minute colonies, rarely larger than a pin 

 head, at first transparent and almost dewdroplike; later 

 they may become somewhat more opaque. In general they 

 grow particularly well upon coagulated blood serum, but 

 not upon potato. In broth the medium is sometimes clouded 

 as a result of the formation of numerous short chains, in 

 other cases it remains clear, the organism evidently growing 

 in the form of long tangled threads as a sediment in the 

 bottom of the tube. 



Physiology.— This organism is aerobic and facultative 

 anaerobic. It grows best at blood heat but growth will 

 usually take place also at room temperature. No pigment 

 is produced and no coagulating or proteolytic enzyme. No 

 gas is produced from any of the sugars, though acid is 

 formed by most strains from many sugars, particularly 

 from dextrose and lactose. Efforts, in part successful, have 

 been made to classify the various strains of streptococci, 



