B A CILLI OF HJEMORRHA GIC SEPTIC&MIA 123 



Pathogenesis. Three types of the disease are common 

 bubonic, septicsemic, and pneumonic. The bacillus is 

 found in the buboes (sometimes with streptococci and 

 staphylococci) in the bubonic form, in the blood-stained 

 (' rusty ') sputum in the pneumonic form, and in the blood 

 in the septicsGmie form. It is also found in the blood in 

 the other forms on the approach of death. The period of 

 incubation appears to be usually from three to six days, 

 but may extend to nine days. 



Pathogenesis for Lower Animals. The injection of 

 cultures into mice, guinea-pigs, and rats, produces plague 

 symptoms, and the animals die in two to seven days. 

 A mere scratch with a needle dipped in an emulsion of 

 a recent culture of plague will generally kill a white 

 mouse of ordinary size in one to three days. Rats and 

 mice can be infected per os. The bacilli are found in 

 the spleen and lymphatic glands of inoculated animals 

 but arfe not very numerous in the blood. 



Calves and poultry may contract the disease in a 

 chronic form, as the result of feeding on plague-infected 

 offal (Simpson). Plague also attacks cats, dogs, ferrets, 

 bats, squirrels, pigs, hares, rabbits, and monkeys. 



Transmission, The plague bacillus probably obtains 

 entrance through wounds in the skin, or through the 

 mucous membrane of the respiratory or (more rarely) 

 alimentary tracts. The sputa of patients with the pneu- 

 monic disease, when discharged in droplets during cough- 

 ing, etc., probably constitutes the main way in which 

 disease spreads in these cases. 



The lower animals often convey the disease. An 

 epizootic among rats is almost constantly seen before 

 the disease becomes epidemic among men, and ground 

 squirrels have been held responsible for epidemics in 

 California. Rats may become infected by ingestion of 

 carcasses of men and animals dead of the disease. When 

 infection is experimentally produced in this way mes- 

 enteric buboes are most frequent. But Jordan says that 

 an examination of 5,000 naturally-infected rats showed 

 no instance of mesenteric bubo, cervical buboes being 

 most often found. Different species of rats vary greatly 

 in regard to their susceptibility to the disease. The 

 white rat is the most susceptible, the brown ship rat or 

 brown dock rat coming next, then the black rat and a 



