172 PATHOLOGY 



fected individuals. Inoculation of cutaneous wounds 

 may also occur, though the bacillus is short lived out- 

 side the body and rapidly disappears from water, soil, 

 and air. The most important mode of infection is by 

 inoculation by the bite of the rat flea. Rats, ground 

 squirrels, mice, guinea-pigs, and monkeys are very sus- 

 ceptible to the disease, and practically every outbreak 

 of the disease among human beings is coincident with an 

 epidemic among rats. If the rats are free of fleas close 

 contact of healthy with infected animals does not in- 

 fect healthy animals, while the mere transference of 

 fleas from infected animals to healthy ones without any 

 association of healthy with infected animals is sufficient 

 to cause an outbreak of the disease among the healthy. 

 It would seem that the pneumonic type is acquired 

 by inhalation of infected material, while the bubonic 

 form is transferred from rats to man by the flea. While 

 rat fleas do not normally attack man, yet upon the 

 death of their normal host they leave the dead body in 

 search of warmth and nourishment, and will then take 

 up their abode temporarily upon the bodies of human 

 beings. 



Morbid Anatomy. There is swelling and inflammation 

 of the lymphatic glands, which tend to suppurate. The 

 inflammation sometimes extends to the adjacent tissues 

 with extravasations of blood. The inguinal glands are 

 most constantly affected, though those of the axilla, 

 neck, and mediastinum may also be affected. 



