144 BACTERIA 



PLAGUE BACILLUS. 



Bacterium Pestis. 



Plague Bacillus. (Fig. 44.) 



Morphology and Stains. Short plump rods with rounded ends, 

 containing no spores and non-motile. Also surrounded by cap- 

 sule? Organisms from exu dates, or blood, exhibit character- 

 istically peculiar polar staining. They are often found 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 22 C., but best at 37 C.; 



FIG. 45. Colonies of plague bacilli forty-eight hours old. (Kolle and 



Wassermann.) 



is killed after a short exposure to 55 C. 60 C., 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 



