THE STREPTOCOCCUS PYOGENES. 255 



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 cul- 

 tures 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 endogenous spores. Under artificial conditions 

 we have no reason to believe that it enters a stage 

 where its resistance to detrimental agencies is increased. 

 In the tissues of the body, however, it appears to pos- 



