BUBONIC PLAGUE 239 



is non-motile, and does not form spores. According to 

 some observers, the organism is encapsulated. 



Method of Staining. — The organism is easily stained by 

 the ordinary dyes, but is not stained by Gram's method. 



KoUe (Deut. med. Woch., March 4, 1897) says that in 

 cover-glass preparations from the pus of the buboes there 

 are, besides pus cells, detritus, and red blood cells, abundant 

 bacilli with rounded ends. Both ends of this micro-organism 

 stain deeply, whereas the central portion hardly stains at 

 all. This peculiarity of staining is not really seen in any 

 other microbe pathogenic to man. 



Growth on Media. — The bacillus grows slowly at a 

 temperature from 18° to 20° C, and very rapidly at 37° C. ; 

 in twenty-four hours an abundant growth may be obtained 

 on almost any media. The culture in broth is very 

 characteristic : a flocculent, wavy deposit is formed, which 

 settles to the bottom of the liquid, leaving the upper portion 

 clear. 



In old broth cultures there is formed an abundant curd- 

 like deposit, and a thin filmy membrane on the surface. 

 The bacillus grows readily on most of the various media — 

 gelatine, agar, blood-serum, potato, etc. On the surface of 

 gelatine it forms a thick shining white or cream-coloured 

 growth, which is confined to the inoculation streak; the 

 medium is not liquefied. 



Cultures appear to quickly lose their virulence, and it 

 has been found that though many of the least virulent 

 cultures grow most rapidly, yet, upon testing them on 

 rabbits and guinea-pigs, they have lost almost all their 

 toxic properties. The culture in broth is alkaline ; it does 

 not appear to curdle milk. 



Distribution and Occurrence.^The typical bacillus is 

 present in all cases of plague. As in other affections, 

 the streptococcus is found as a secondary infection. 



