THE BACILLUS OF BUBONIC PLAGUE. 317 



tional important contributions to our knowledge of 

 the subject. The results of these studies demonstrate 

 that bubonic plague is an infectious, not markedly con- 

 tagious, disease that depends for its existence upon the 

 presence in the tissues of a specific micro-organism 

 the so-called plague or pest bacillus. 



This organism is described as a short, oval bacillus, 

 usually seen single, sometimes joined end to end in pairs 

 or threes, less commonly as longer threads. It stains 

 more readily at its ends than at its centre. It is some- 

 times capsulated ; is non-spore-forming ; is aerobic, and 

 is non-motile. It is found in large numbers in suppu- 

 rating glands, and in much smaller numbers in the cir- 

 culating blood. (Fig. 61.) 



It is demonstrable in cover-slip preparations made 

 from the pus and in sections of the glands by the ordi- 

 nary staining-methods. 



Wilm l has found it by culture methods in the spleen, 

 lungs, liver, kidneys, stomach, walls of the intestine, 

 urine, and intestinal contents of fresh cadavers; and 

 during life in the blood, expectoration, fa3ces, and urine 

 of patients sick of plague. He failed to find it in the 

 perspiration. 



Yersin states that it does not retain the color when 

 treated by the method of Gram ; while Kitasato says 

 that it at one time stains by this method and at another 

 it becomes decolorized. Aoyama observed that those 

 bacilli within the suppurating glands were decolorized, 

 while those in the blood retained the stain when treated 

 by Gram's method. 



Since there is often a mixed infection in these cases, 

 it appears likely that the above discrepancy may be 



1 Wilm: Hygiciiisuhc Kundsclmu, 181)7, p. 217. 



