THE BACILLUS OF BUBONIC PLAGUE. 273 



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

 suppurating glands, and in much smaller numbers in 

 the circulating blood. (Fig. 60.) 



It is demonstrable in cover-slip preparations made 

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

 nary staining-methods. Yersin states that it retains 

 its 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 

 attributed to individual peculiarities of different species 

 of bacteria that were under examination. 



It may be cultivated upon ordinary nutrient media. 



The most favorable temperature for its growth is 

 between 36 and 39 C. Its colonies on glycerin agar- 

 agar and on coagulated blood-serum are described as 

 iridescent, transparent, and whitish. On gelatin at 

 18-20 C. it develops as small, sharply denned, white 

 colonies. In stab-cultures it develops both on the sur- 

 face and along the track of the needle. Its growth is 

 slow. It does not cause a diffuse clouding of bouillon, 

 but grows rather as irregular, flocculent clumps that 

 adhere to the sides or sink to the bottom of the vessel, 

 leaving the fluid clear. 



It is pathogenic for mice, rats, guinea-pigs, rabbits, 

 and sheep. Pigeons are immune. The animals suc- 

 cumb to subcutaneous inoculation in from two to three 

 days. According to Yersin, the site of subcutaneous 

 inoculation becomes oedematous and the neighboring 



