HEMORRHAGIC SEPTICEMIA GROUP 307 



in stained mounts from the pus from a bubo as a small gram- 

 negative bacillus, with characteristic bipolar staining. It may 

 also be isolated upon culture-media and identified by its growth 

 characteristics. 



Transmission. The pneumonic form of the disease may be 

 transmitted by the inhalation of infectious droplets. Plague is 

 not known to occur in the human following ingestion of the or- 

 ganism. The bubonic or most common type is probably trans- 

 mitted to man by the bite of fleas (or from their excretions scratched 

 into the skin), which have left rats dead of the disease. An epi- 

 demic of plague in the human is commonly preceded by an epizo- 

 otic among the rats of the community. It has been shown ex- 

 perimentally that a flea may transmit the disease from an infected 

 to a non-infected individual. It is also known that the cannibal- 

 istic tendency of the rats to eat their dead is in part responsible 

 for the spread of the disease among vermin. The annihilation 

 of the rat is the best prophylaxis known. The disease has in 

 certain places, as about San Francisco, been found to spread to 

 such rodents as the ground-squirrels and wood-rats. When a 

 region once becomes thoroughly infected, it is, therefore, difficult 

 to stamp out the disease. 



