OTHER IMPORTANT PATHOGENIC MICRO-ORGANISMS 173 



In diagnosing the infection in horses serum examina- 

 tions are of service. The serum is tested by means of 

 complement fixation and agglutination reactions. The 

 animals can also be tested by means of "mallein" (made 

 from glanders bacilli), the injection of mallein being fol- 

 lowed by a typical febrile reaction. 



Bubonic Plague Bacillus. Short, thick rods with 

 rounded ends, Gram-negative, aerobic, and non-motile. 



Fig. 57. Bacillus pestis (bubonic plague) in smear from rat's liver, 

 showing bipolar staining; X 720 (Wherry). 



In man the infection occurs in two forms: the bubonic, 

 involving the lymph-glands; the pneumonic, involv- 

 ing the lungs. The disease is spread directly from man 

 to man, especially in the pneumonic form, and also 

 from rats, ground squirrels, and other rodents to man. 

 In the latter case infection is usually intermediate through 



