THE CONQUEST OF DISEASE 



ter. By inoculating guinea pigs, it was found 

 that many of the ground squirrels were in- 

 fected with plague, their fleas carrying the 

 infection from one to another. Already 

 plague-infected squirrels have been found in 

 eight other adjoining counties, covering an 

 area of five thousand square miles. So long as 

 the fleas remain with the squirrels, the human 

 danger is not great; but when other animals, 

 such as rats, dogs, and cats, which harbor fleas, 

 and which live in close relation to man, become 

 the hosts of fleas which have come from infected 

 squirrels, the danger becomes a serious one. 

 It is through the agency of these house-dwell- 

 ing animals that the disease is most apt to be 

 conveyed to man. Within the last few months 

 in 1909, three cases of human plague have 

 occurred in Alameda County, California, de- 

 veloping unexpectedly as isolated cases. A 

 local laboratory, which is doing excellent work, 

 has been established for the study of plague. 

 It should command the admiration of every 

 American. The workers protect themselves 

 by being vaccinated with the prophylactic of 

 Haffkine. Their efforts are not only of local 

 importance, but are full of significance for the 

 whole continent. Of this work, some day it 



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