INSECTS AND DISEASE 373 



frequently, or be kept covered so that the mosquitoes cannot 

 get to the water in them. All tin cans, or other scattered 

 receptacles that might hold a little water, should be removed or 

 placed so that water will not stand in them. Small ponds 

 should be drained or kept covered with a film of oil during the 

 summer time. Larger ponds are usually naturally stocked 

 with fish, predaceous insects and other enemies of mosquito 

 larvae and pupae, so that they are not a source of danger unless 

 the margins are filled with rushes or other strong plant growth. 

 Mosquitoes will not breed in running streams, but the quiet 

 pools along the sides may afford excellent breeding places, 

 particularly if they are cut off from the rest of the stream. 

 Many species breed abundantly in wet pastures or meadows, 

 and others abound in the brackish tide pools in the marshy 

 land along sea-coasts. Such marshes must be drained or 

 dyked so the water will not remain on them, or all the little 

 pools must be covered with oil if such regions are to be freed 

 from these pests. 



Yellow Fever and Mosquitoes. For many years the cause 

 and method of dissemination of yellow fever was a puzzle to 

 physicians and scientists. The disease was always regarded 

 as highly contagious as well as infectious, and every effort was 

 made to isolate patients and to establish strict quarantines in 

 infected regions. But all such methods proved unsatisfactory. 

 Many people became ill without ever having been near a yellow 

 fever patient, while others worked in daily contact with sick 

 persons yet did not take the disease. 



During the American occupation of Cuba in 1900 yellow 

 fever became very prevalent there and a board of army 

 medical officers, known as the Yellow Fever Commission, was 

 appointed to study the disease and try to find some means to 

 control it. Some years previously a physician had suggested 

 that a certain species of mosquito, Stegomyia fasdala (calopus), 

 which was always found in regions where the yellow fever oc- 

 curred, might be concerned in the transmission of the disease. 

 The Yellow Fever Commission early decided to put this theory 

 to the test, and before their experiments had been finished it 

 was shown that yellow fever was transmitted by this mos- 



