l62 



BACTERIA 



PLAGUE BACILLUS 



Bacterium Pestis. 



Plague Bacillus (Fig. 42). 



Morphology and Stains. Short plump rods with rounded ends, 

 containing no spores and non-motile. It is said by some that a 

 capsule is formed. Organisms from exudates, or blood, exhibit 

 characteristically peculiar polar staining. They are often found 



FIG. 42. Pest Bacilli from spleen of rat. (Kolle and Wassermann.) 



within the leucocytes. In bouillon the organism grows in long 

 chains; is stained with all the common basic dyes, but is not 

 colored by Gram's method in cultures. It exhibits a great variety 

 of involution forms when grown in salty culture media (3^ 

 percent salt). 



Relation to Oxygen. Strict aerobe, the growth is stopped by 

 the exclusion of oxygen. 



Vital Requirements. Grows well at 22C., but best at 35C.; 

 is killed after a short exposure to 55-6oC., stands drying from 

 four to eight days, and dies in water after a week. In the buried 

 bodies of man and animals it lives from twenty-two to thirty-eight 

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

 or chemicals very long. 



