11 



Africa a similar disease of cattle is transferred by the bite of the 

 famous biting- fly Ivnown as the tsetse fly (fig. 13). The germs of 

 the disease of cattle known as anthrax are carried by gadflies, or horse 

 flies, and when these flies subsequently bite human beings malignant 

 pustules may result (see fig. 11: for one of these gadflies); and other 

 discoveries of this nature are constantly being made. Even the com- 

 mon bedbug (fig. 15) is strongly suspected in this connection. 



YELLOW FEVER. 



One of the most important of these disease-transfer relations of 

 insects which has been demonstrated is the recently proved carriage 

 of yellow fever by certain mosquitoes. The cause of yellow fever has 



always been a mys- 

 tery, and indeed it is 

 a mysterj^ to-da}'^ in 

 a measure, since al- 

 though undoubtedly a 

 disease of parasitic 

 origin, the parasitic 

 organism itself has 

 not yet been discov- 

 ered. During the 

 summer and autumn 

 of 1900 and spring and 

 summer of 1901 the 

 work of a commission 

 of surgeons of the 

 United States Armj' 

 has demonstrated in 

 Cuba beyond the 

 slightest possible 

 doubt that yellow 

 fever is not conveyed 

 by irffected clothing of yellow-fever patients or by contact with such 

 patients or by proximity to them, but that it is conveyed by the bite of 

 a certain species of mosquito known as Stegomyia fasciata (fig. 16), 

 which abounds in regions where yellow fever is possible. The bite of 

 this mosquito, however, does not convey yellow fever to a healthy per- 

 son until twelve days have elapsed from the time when the same mos- 

 quito has bitten a person suffering with the disease. It follows from 

 this fact that by keeping yellow-fever patients screened from the pos- 

 sibilities of mosquito bites we can prevent the yellow-fever mosquito 

 from becoming infected. It follows further that by preventing healthy 

 people from being bitten by mosquitoes we can keep them free from 

 the disease even where infected mosquitoes exist. And it follows still 



Fig. 16.— Steg^omyia/a^etato— enlarged (author's illustration). 



