138 BACTERIOLOGY FOR NURSES 



filth, bad air, poor and insufficient food, and intemper- 

 ance. It may be said that epidemics of plague have 

 never occurred where hygienic conditions exist. 



The plague bacillus was simultaneously discovered 

 and described by Yersin and Kitasato from observa- 

 tions made during the epidemic at Hong Kong in 

 1894. Plague bacilli are small oval rods, somewhat 

 shorter than the typhoid bacillus and of about the 

 same thickness, although considerable variation in 

 size occurs. The rods have rounded ends, and in 

 staining, the middle portion is usually left uncolored, 

 giving the so-called " polar-staining." The bacillus 

 may be described as short, oval, capsulated, non- 

 motile, non-spore-bearing, and polar-staining. It 



grows luxuriantly 

 on solidified blood- 

 serum as a yellowish 



FIG. 23. Bacillus of bubonic plague, show- ~ v ~ v ^pnosit PTOW- 

 ing polar-staining. &*$ ' >ll > & F( 



ing in shred-like 



films which adhere to the sides or drop to the bot- 

 tom of the culture tube. Growth is best at a 

 temperature between 36 C. and 39 C. (96.8 F.- 

 102.2 F.). It is destroyed by drying at room 

 temperature in four days; by exposure to sunlight 

 in four hours; by moist heat at 100 C. (212 F.) 

 instantly, and at 80 C. (176 F.) in five minutes; 



