Staining 627 



forms. Of these, the bubonic form is most frequent and the 

 pneumonic form most fatal. 



The infection usually takes place through some peripheral 

 lesion, but may occur by inhalation of the specific or- 

 ganisms. 



The bacillus of bubonic plague (Fig. 186) was indepen- 

 dently discovered by Yersin * and Kitasato f in the summer 

 of 1894, during an epidemic of the plague then raging at 

 Hongkong. There seems to be little doubt but that the 

 micro-organisms described by the two observers are identical. 



Morphology. The bacillus is quite variable. Usually it 

 is short and thick, a "cocco-bacillus," as some call it, 

 with rounded ends. Its size is small (1.5 to 2 fJ. in length) 



-% 



* -1 ,. * * 



Fig. 1 86. Bacillus of bubonic plague (Yersin). 



and 0.5 to 0.75 in breadth. It not infrequently occurs in 

 chains of four or six or even more, and is occasionally en- 

 capsulated. It shows active Brownian movements, which 

 probably led Kitasato to consider it motile. Yersin did not 

 regard it as motile, and was correct. GordonJ claims that 

 some of the bacilli have flagella. No spores are formed. 



Staining. It stains by the usual methods; not by 

 Gram's method. When stained, the organism rarely 

 appears uniformly colored, being darker at the ends than 



* "Ann. de 1'Inst. Pasteur," 1894, 9. 



t Preliminary notice of the bacillus of bubonic plague, Hong- 

 kong, July 7, 1894. 



t "Centralbl. f. Bakt. u. Parasitenk.," Sept. 6, 1897, Bd. xxn, 

 Nos. 6 and 7, p. 170. 



