PLAGUE BACILLUS 145 



days. Withstands freezing for months, but does not stand light 

 or chemicals very long. 



Cultures. Grows very well on culture media. In bouillon 

 it thrives abundantly, with a heavy pellicle which produces depend- 

 ent stalactites that drop to the bottom of the vessel. On gelatine 

 plates it grows in small flat colonies, which are gray and transpar- 

 ent, and which do not liquefy the gelatine. (Fig. 45.) In gelatine 

 tubes it forms a faint thread-like line, without liquefying the media. 

 On agar the growth is whitish and abundant, and resembles the 

 colon bacillus. Old cultures are luxuriant. Milk is not coagulated, 

 and the growth is slight. Potato yields a slow whitish-yellow 

 growth that is sharply outlined. 



Chemical Activities. Does not produce H 2 S, enzyme, colors, 

 or odors, indol or nitrites. The toxin produced is not soluble and 



FIG. 46. B. Pestis in pus of bubo. (Jackson.) 



the nitrate is non-poisonous. Old killed bouillon cultures can be 

 extracted and a highly poisonous substance precipitated therefrom 

 with alcohol, or ammonium sulphate, that is lethal for mice. 



Habitat. Never found in healthy human bodies. In persons 

 afflicted with plague, the organism is widely distributed in buboes 



