PATHOGENIC BACTERIA. 



243 



Staphylococcus pyogenes aureus. A micrococcus of 

 variable size, arranged in irregular clumps, sometimes in 

 pairs; about .8 to .9^ in diameter; not motile (Fig. 55). It 

 stains by Gram's method; it is facultative anaerobic; 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 pro- 

 duction of gas but produces various acids. 



FIG. 55. 



Staphylococcus pyogenes aureus, Pure Culture. (X 1000.) 



The growths in the first place are pale, subsequently 

 becoming 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 

 requires a temperature of 90 to 100 C. to destroy it. It 



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