Fleas and Plague 1 53 



when it is crushed by the annoyed host. The 

 latter is probably the most common method of in- 

 fection, for the bacilli that are liberated when the 

 flea is crushed may readily be rubbed into the 

 wound made by the flea bite or into abrasions of 

 the skin due to the scratching. Kill the flea, but 

 don't "rub it in." 



During the recent outbreak in San Francisco 

 many thousand fleas that were infesting man, rats, 

 mice, cats, and dogs, squirrels and other animals 

 have been studied and it has been found that while 

 each flea species has its particular host upon which 

 it is principally found, few if any of them will hes- 

 itate to leave this host when it is dead and attack 

 man or any other animal that may be convenient. 



COMMON SPECIES OF FLEAS 



Throughout India and in all the warm climates 

 where plague frequently occurs the most common 

 flea found on rats has come to be known as the 

 plague flea (Lcemopsylla cheopus) (Figs. 105, 106), 

 and is doubtless the principal species that is con- 

 cerned in carrying the disease in those climates. 

 It now occurs quite commonly on the rats in the 

 San Francisco Bay region and is occasionally 

 found there on man also. In the United States, 

 Great Britain and other temperate regions another 



