MICROBIAL DISEASES OF MAN AND ANIMALS. 625 



Kitasato independently in 1893. They found it in glands and through- 

 out the body in fatal cases. 



The organism is readily grown from the buboes; the blood, and the sputum in the 

 pneumonic type, by simple inoculation of ordinary media of a slightly alkaline reac- 

 tion. The bacteria are i.$fji to 1.7/1 long by 0.55^ to o.j/n wide with rounded ends 

 occurring singly or in pairs and short chains in exudates and sometimes in long 

 chains in broth. Involution forms, large swollen spheres, clubs, etc., are characteristic 

 in artificial media. There are no spores. It is non-motile. Some observers have 

 demonstrated a gelatinous capsule. Occasionally very distinct branching occurs (Hill). 

 Stain easily with aniline dyes, particularly at the poles which may show round or oval 

 granules. It is Gram-negative. Its minimum temperature for growth is about 12, 

 the optimum 30, the maximum 40. It is aerobic. On agar after twenty -four hours 



FIG. 107. Baa. pestis. (After Yersin from Williams.') 



shows small granular grayish colonies with a thickened center and indented margin. 

 Broth shows a granular deposit and sometimes a pellicle with dependent outgrowths, 

 the medium remaining otherwise clear. Gelatin growths are as on agar, and the 

 medium is not liquefied. Litmus milk may show slight acid formation and no coagu- 

 lation. Potato shows nothing characteristic. The toxins appear to be largely endo- 

 toxins, though soluble poisons have been found in old cultures. No indol is formed. 

 Resistance toward heat is not great, boiling kills in a few minutes. Light kills in a 

 few hours. They do not resist drying well, but in a moist condition remain viable 

 for over a year. The usual strengths of ordinary disinfectants kill in about ten 

 minutes. 



Rats, mice, guinea-pigs, rabbits, and monkeys are particularly suscep- 

 tible to inoculation and even insects die from infection. 



The bacterium enters the body through the (usually abraded) skin or 

 40 



