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1. — The yejlow-fever mosquito (Aedes calopus) Stegomyia 

 fasciata : Adult femaleMuch enlarged. (Howard) 



his experimental camp ]\Iajor Reed and his associates proved that yellow fever 

 could not be transmitted by contact with yellow fever patients, but only by the 

 bites of infected mosquitoes, except by the artificial injection of diseased blood. 

 The causal organism has not yet been discovered on account of its being a filter- 

 able virus. It is known, however, that a 12-day incubation period is required in 

 Stegomyia before its bite becomes infectious to a second person. Moreover, the 

 mosquito can obtain infected blood from a patient during only the first three 

 days of his disease. 



Based on these facts, the control of yellow fever has become an easy mat- 

 ter. The patients are isolated as soon as the disease appears, and standing water 

 in which Stegomyia might develop is treated with kerosene. Besides, all rooms 

 in the building and adjacent buildings are fumigated, for the purpose of destroy- 

 ing living mosquitoes. 



Culex Mosquito and Filariasis. — The tropical disease, Filariasis, is caused 

 by a minute nematode worm, Filaria, which lives in the blood of man and cer- 

 tain species of Culex (C. fatigans). The worms escape from the mid-intestine of 

 the mosquito into the muscular tissue where they grow for two or three weeks. 

 They then migrate to other portions of the body and often collect at the base 

 of the proboscis, whence they are carried into the human blood circulation. Some- 

 times the worms become three or four inches long and obstruct the lymphatic 



