408 THE HEMORRHAGIC SEPT ICE MI A GROUP 



containing bile salts, particularly sodium taurocholate ; the other 

 organisms will not grow in this medium. 



Bacillus Pestis. Plague, the most dreaded of the acute epidemic 

 diseases, has at somewhat irregular intervals swept over parts of the 

 Orient, and during the earlier centuries of the Christian era even 

 invaded Europe. The great epidemics of the third and the fourteenth 

 centuries caused widespread death; literally millions perished, and 

 the effect upon the residual population was most distressing. The 

 disease has recently become endemic on the western coast of the 

 United States, the reservoir of infection being certain rodents. 



FIG. 58. Plague bacillus, bouillon culture, methyl ene-blue stain showing bipolar 

 staining. X 1000. (Kolle and Hetsch.) 



The causative organism, Bacillus pestis, was isolated and described 

 almost simultaneously by Kitasato 1 and Yersin 2 from the purulent 

 contents of buboes, the lymph glands, the blood and the cerebrospinal 

 fluid. Later the specificity of the organism was established by labora- 

 tory accidents and by the very comprehensive studies of the British 

 Indian Plague Commission. 



Morphology. Bacillus pestis is a small thick bacillus with rounded 

 ends, wilich occurs singly or in pairs as a rule, although short chains 

 of three to six elements are occasionally seen. The organism is not 

 characteristically rod-shaped, rather it approaches in outline a some- 

 what ovoid cell. The size varies within the comparatively narrow 

 limits of 0.5 to 0.7 micron in diameter at the widest part and 1.5 

 to 1.8 microns in length. The bacilli are very pleiomorphic and exhibit 

 great variation in size and shape according to the medium and age 



1 Lancet, 1894. 2 Ann. Inst. Past., 1894, p. 662. 



