THE STREPTOCOCCUS PYOGENES. 229 



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 has been added, produce a very 

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

 this change in color is not apparently due to the pro- 

 duction of acidity, as there is no coagulation, and the 

 reaction of the milk when tested by delicate litmus or 

 by curcuma paper is sometimes seen to be still slightly 

 alkaline, and to remain so for several weeks. 



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, being a micrococcus, does not 

 form 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 possess a 



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