242 MANUAL OF BACTERIOLOGY. 



by Gram's method; it is a facultative anaerobe; grows rapidly, 

 best at 30° to 37° C. It liquefies gelatin. Upon gelatin plates 

 small colonies appear at the end of about two days. It grows 

 well upon all the culture-media. Milk is coagulated. It does 

 not lead to fermentation with the production of gas, but pro- 

 duces various acids. 



The growths in the first place are pale, subsequently be- 

 coming golden-yellow in color, but only in the presence of 

 oxygen. This color appears well on all media, and is especially 

 distinct on potato. Sometimes the color is slow in developing. 



In a fresh, moist condition the organism is killed by ten 

 minutes' exposure to 58° C. ; in a desiccated condition it re- 

 quires a temperature of 90° to 100° C. to destroy it. It is not 

 killed by drying. In the same specimen the micrococci may 

 have quite different resisting powers to chemical germicides. 

 Some of the individual cells are destroyed by i-iooo solution 

 of bichloride of mercury in five minutes; others survive ex- 

 posure to this solution for from ten to thirty minutes. (Abbott.) 



Sterihzed cultures introduced into animals may produce local 

 suppuration. The cells contain intracellular toxic substances 

 and otoxins.* 



As has already been mentioned, the Staphylococcus pyo- 

 genes aureus is the commonest of the pyogenic bacteria in man. 

 It has been obtained from a great variety of sources, and ap- 

 pears to be able to exist as a saprophyte. It has been found 

 on the skin, iii the mouth, in the nasal and pharyngeal mucus, 

 and also in the ahmentary canal. It has furthermore been de- ' 

 tected in the air and in dust. It appears to find the conditions 

 necessary for its existence in the vicinity of human habitations. 



Cultures of the Staphylococcus pyogenes aureus vary con- 

 siderably in virulence. These variations are sometimes to be 

 explained through cultivation on unfavorable media or repeated 



* Morse. Journal Experimental Medicine. Vol. I., p. 613. 



