246 ENTOMOLOGY 



that plague is transmitted from rats to man by several species of fleas 

 and also by bedbugs. Verjbitski, whose experiments on this subject 

 were particularly precise and thorough, found that plague can be con- 

 veyed by the bites of these insects and that the opening made by the bite 

 affords entrance to plague bacilli when the bodies of the insects are 

 crushed or when the infected feces are introduced by the rubbing or 

 scratching of the wound. 



The species of rat-flea most common in the orient is the cosmopolitan 

 "plague flea," Lcemopsylla cheopus. 



In the United Sates the most common rat flea is Ceratophyllus fascia- 

 tus. The common cat and dog flea, Ctenocephalus canis, affects rats as 

 does also the human flea, Culex irritans; and all these species are known 

 to bite man. 



Plague in San Francisco. Plague, long dreaded in American sea- 

 ports, finally entered San Francisco in 1900, killed 114 persons in the 

 next four years, became dormant and broke forth again, with violence, 

 in 1907. The city, just beginning to recover from the great fire of the 

 year before, was in a frightful sanitary condition and most of the popula- 

 tion, engaged in the work of reconstruction, paid little attention to the 

 deaths from plague and at first gave little aid toward the suppression 

 of the disease. As may be imagined, the campaign against the disease 

 undertaken by the U. S. Public Health and Marine-Hospital Service was 

 carried on in the face of great odds. It was, however, conducted most 

 efficiently and successfully under the command of Dr. Rupert Blue 

 (now Surgeon-General), who wisely attacked the disease by attacking 

 the rat population. 



The labor involved in starving out the rats, trapping or poisoning 

 them, and making buildings rat-proof by the use of concrete or sheet 

 iron, was immense; but the undertaking was nevertheless carried to a 

 successful conclusion. More than one million rats were killed and the 

 disease was checked. 



In California plague affects ground squirrels, which doubtless con- 

 tract the disease from the rats that use the runways of the squirrels in the 

 fields. 



TRYPANOSOMIASES 



Some of the diseases known as trypanosomiases are among the dead- 

 liest that affect man and other vertebrates, and pathogenic trypanosomes 

 the organisms causing these diseases have received an immense 

 amount of study during the last fifteen years. 





