BACILLUS PESTIS 233 



in Bombay, the figures from the former have not much influence on 

 the figures from India. McCoy has once or twice seen rats dead from 

 plague which did not show any of the characteristic pathologic 

 changes. In these cases the presence of the plague bacillus was 

 established by animal inoculation. 



Plague-infected rats generally die in a few days, but sometimes, 

 though rarely, the plague runs a chronic course. The Indian Plague 

 Commission encountered a considerable number of these chronic 

 cases in two villages in the Punjab Province. 



Animals Susceptible. According to Simpson, Hunter, and others, 

 rats are by no means the only animals susceptible to natural plague 

 infection; these authors also mention pigs, calves, sheep, monkeys, 

 geese, ducks, turkeys, hens, pigeons, and quails. It is, however, very 

 probable that this claim is not quite correct, and that other members 

 of the group of hemorrhagic septicemia bacilli (Bacillus bipolaris) 

 have been mistaken for the Bacillus pestis. Other rodents which, 

 according to Blue, have been shown to harbor the Bacillus pestis, and 

 to be a subject to plague infection, are the tarbegan, a species of 

 arctomynse, found in Siberia; the marmot, a hibernating rodent of 

 India and China; the marmot of Thibet, the tree squirrel, and the 

 California ground squirrel (Otosperphilus beecheyi). According to 

 Blue and Wherry four plague-infected ground squirrels were found 

 in California during the summer of 1907, and it was possible to 

 show that several persons had contracted plague directly from this 

 animal. 



Spreading of the Infection. Plague infection in man and animals is 

 generally a wound infection, near which most cases present plague 

 buboes. A certain percentage of cases are probably due to inhalation 

 and lead to the pneumonic type. It is now claimed, particularly upon 

 the basis of the early investigations of Simond and the more recent 

 and extensive work of the Indian Plague Commission and the Advisory 

 Plague Committee that the rat flea is responsible for the spread of 

 plague from rat to rat and from rat to man. This flea most common 

 on rats in tropical and subtropical countries has been described by 

 Rothschild as Pulex chceops. About the same time the author, in 

 ignorance of Rothschild's work, independently found and described 

 the rat flea in Manila under the name of Pulex philippinensis. It 

 is now claimed that the rat flea will frequently bite man, although in 

 the author's experiments it did not. If plague is conveyed from rat 

 to rat by the flea, it is certainly strange that most of the buboes in the 

 rats in India, i. e., 75 per cent., are found in the cervical region, which 

 would indicate that fleas bite rats most commonly on the head and 

 not on the body. The very frequent occurrence of the cervical bubo 

 was formerly explained on the assumption that rats generally infected 

 themselves by small abrasions or wounds in the mouth. It is also 

 well known that even among well-fed white rats the living eat the 

 dead of their own species. 



