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 fever 
patient 1s harmless and in the absence of a patient the mos- 
quito is harmless (Sternberg). The disease terminates in 
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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