THE STREP10COCCUS PYOGENES. 245 



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 inoculated, 

 and microscopic examination shows that a multiplication 

 of the organisms placed at this point has occurred. 



In milk its conduct is not always the same, some 

 cultures 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 a very 

 faint pink color after twenty-four hours at 37.5 C. ; 

 there is no coagulation. 



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. When virulent, its virulence is said by 

 Petruschky to be preserved by retaining cultures in the 

 ice-chest after they have been growing on gelatin for two 

 days at 22 C. 



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, being a micrococcus, does not 

 form endogeneous spores. Under artificial conditions we 



