STREPTOCOCCUS PYOGENES. 279 



ture of the body (37.5 C.), and its least on gelatin at 

 from 18 to 20 C. 



On blood-serum its colonies present little that is char- 

 acteristic ; they appear as small, moist, whitish points, 

 from 0.6 to 0.8 mm. in diameter, that are slightly ele- 

 vated above the surface of the serum. They do not 

 coalesce to form a layer over the surface, but remain as 

 isolated colonies. 



On potato no visible development appears, but after 

 a short time (thirty-six to seventy-two hours) there is 

 a slight increase of moisture about the point of inocula- 

 tion, and microscopic examination shows that multiplica- 

 tion of the organisms placed at this point has occurred. 



In milk its conduct is not always the same, some cult- 

 ures causing a separation of the milk into a firm clot 

 and colorless whey, while others do not produce this 

 coagulation. The latter, when cultivated in milk of a 

 neutral or slightly alkaline reaction, to which a few 

 drops of litmus tincture have been added, produce, as a 

 rule, only a very faint pink color after twenty-four hours 

 at37.5*C. 



In bouillon it grows as tangled masses or clumps, 

 which upon microscopic examination are seen to consist 

 of long chains of cocci twisted or matted together. 



It grows best at the temperature of the body (37.5 

 C.), and develops, but less rapidly, at the ordinary room- 

 temperature. 



It is a facultative anaerobe. 



It stains with the ordinary aniline dyes, and is not 

 decolorized when subjected to Gram's method. 



It is not motile, and does not form endogenous spores. 

 Under artificial conditions we have no reason to believe 

 that it enters a stage in which its resistance to detri- 



