PLAGUE BACILLUS 163 



Cultures. Grows very well on culture media. In bouillon it 

 thrives abundantly, with a heavy pellicle which produces dependent 

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

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

 parent, and which do not liquefy the gelatine (Fig. 43). In gela- 

 tine 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 



FIG. 43. Colonies of plague bacilli forty-eight hours old. (Kolle and 



(Wassermann.) 



is not coagulated, but a faint acidity appears. Potato yields a 

 slow whitish-yellow growth that is sharply outlined. 



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

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

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

 be extracted and a highly poisonous substance precipitated there- 

 from 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 

 and in the cutaneous pustules, lymphatics and in the lungs in 

 plague pneumonia; more rarely in the blood and other organs. 



