INSECTS IN RELATION TO OTHER ANIMALS 305 



and the inoculation of a healthy subject. The disease fol- 

 lowed the bite of an infected Stegomyia with remarkable 

 precision. 



Furthermore, Dr. Reed and his associates found that yel- 

 low fever could not be conveyed by means of the clothing, 

 bedding, etc., of fever patients, so long as mosquitoes were 

 excluded. In the absence of the mosquito the yellow feve.r / 

 patient is harmless and in the absence of a patient the mos- 

 quito is harmless (Sternberg). The disease terminates ini 

 cold weather with the disappearance of the mosquito. 



Preventive measures based upon these recently acquired 

 facts have been wonderfully successful. The city of Havana, 

 in which yellow fever had always prevailed, has now been 

 freed of the disease. 



The specific cause of yellow fever has as yet eluded detec- 

 tion in the human body. There has been discovered, how- 

 ever, in the stomach and salivary glands of mosquitoes in- 

 fected with yellow fever, a protozoan parasite (order Coc- 

 cidiida), the sexual cycle of which, ending in the development 

 of sporozoites, has been traced in the body of the Stegomyia. 

 This coccidium may or may not prove to be concerned in the 

 transmission of the disease. 



Other Diseases. Typhoid fever is transmitted frequently 

 by the common house fly, which may carry the bacillus from 

 the excreta of typhoid patients to food supplies in kitchens or 

 elsewhere. The spread of the disease in army camps is due 

 chiefly to the house fly (Musca domestica) , as was demon- 

 strated in 1898 by a commission of the United States army. 



The dreaded disease filariasis (elephantiasis) of Oriental 

 tropical regions is transmitted by mosquitoes of the genus 

 Culex, as Dr. Manson discovered many years ago. The dis- 

 ease is due to a parasitic worm (Filaria), both sexes of which 

 lodge in the lymphatic vessels, obstruct the flow of the lymph 

 and thereby cause an abnormal enlargement of the parts in 

 which they occur. The embryos of the parasite pass into the 

 blood and thence into the body of the mosquito; there they 



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