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544 person, after which the Stegomyia remains infectious for a long period and may be responsible for a series of new cases. These facts were first discovered during the summer of 1900 by a Yellow Fever Commission consisting of Drs. Reed, Carroll, Lazear and Agramonte, of the U. S. Army. Two of these men, Carroll and Lazear, allowed themselves to be bitten by infected mosquitoes, and Lazear died from a severe case of fever thus contracted.

Little further has since been learned of the etiology of yellow fever, but wonderful strides have been made in the application of these simple facts for its eradication. In Cuba, where the commission conducted their investigations, the first attempts were made, and in 1902 yellow fever had been entirely eliminated in Havana. Other West Indian islands were formerly badly infested with yellow fever, but at the present time there is little more danger from this disease there than in the United States. Rio de Janeiro was once a hot bed for yellow fever, but it too has yielded to the destruction of mosquitoes and the screening of patients, till after a six years' fight, the fever has vanished. Still more remarkable are the results accomplished in the Panama Canal Zone under the direction of Dr. Gorgas. Here the warfare against yellow fever has gone hand in hand with anti-malarial work and the isthmus has been transformed from a veritable death-trap to a condition which compares favorably with that of any region on earth.

Our own country has suffered from yellow fever in the past, mainly in the south, but extending to southern Illinois in 1878, to Philadelphia in the terrible epidemic of 1793 and even to Boston and into interior New England towns in the earlier days. The last epidemic occurred during the summer of 1905 in New Orleans, where the application of rational methods rapidly checked the spread of the disease and resulted in its complete eradication long before cold weather. The success of this campaign has undoubtedly sounded the death knell of the yellow fever epidemic and panic in the United States, for New Orleans has amply demonstrated what may be accomplished in the control of an epidemic by an efficient group of workers, backed by a sympathetic public and supplied with reasonable funds.

Rocky Mountain spotted fever, an important human disease which occurs in certain parts of the Rocky Mountain region in the northern United States, has been shown to be insect-borne. In this case the vector is a tick, not a true insect, but a member of the arthropod group Acarina, whose members are so much like insects in many ways that it is hardly necessary to make any distinction in the present discussion. In 1902 Wilson and Chowning suggested that ticks might carry this disease, and four years later Ricketts definitely proved such to be the case. Spotted fever occurs in its most severe form with 70-80 per cent, mortality in western Montana, but extends into several other near-by