HEMORRHAGIC SEPTICEMIAS AND PLAGUE 351 



■which devastated many parts of E,urope at the close of the 

 Middle Ages. The disease may also be communicated to 

 man by inhalation, developing as a very fatal type of 

 pneumonia. Inasmuch as the organism is killed by drying, 

 transmission in this manner usually takes place when 

 patients and others come in contact in damp, ill-ventilated 

 quarters. 



It is possible successfully to immunize man against 

 plague by injections of killed or attenuated bacteria or 

 their products. It is also possible to immunize horses and 

 use their sera in combating the disease. Inasmuch as there 

 is little transmission to man except from the rat, it is neces- 

 sary to conduct campaigns against these rodents vs^herever 

 there is danger of an outbreak of a disease. In the United 

 States, outbreaks have been controlled in this fashion in 

 San Francisco, New Orleans and other ports. In some cases, 

 as in San Francisco, it was found that the disease eventually 

 attacked other rodents such as ground squirrels and wood 

 rats. "When once the rodents native to these regions become 

 thoroughly infected, it becomes increasingly difficult, there- 

 fore, to stamp out the disease. 



