It is usually stated that mosquitoes may hibernate during winter following infection in the autumn and that cases of malaria in early Spring may be explained by their bites. Examination of hibernating mosquitoes for zygotes does not give strong proof to this view but such mosquitoes, becoming active with a rise in temperature, may bite gamete carriers in the house and thus spread malaria. Pyrethrum powder, which is set on fire with a little alcohol, may be burned, using 2 pounds per 1000 cubic feet, and an exposure of four hours. This does not certainly kill the insect and the stupified mosquitoes should be swept up and burned. Giemsa’s spray is now considered an excellent measure for killing mosquitoes in rooms. The composition is as follows: Pyrethrum tincture (20 parts powdered pyrethrum blossoms to 100 parts alcohol), 480 grams; odorless potash soap, 180 grams; glycerine, 240 grams. Before using it dilute with 20 times its own weight of water, and spray the walls of the room with a spray pump. The use of a small square of wire gauze on a handle (fly swatter) to kill mosquitoes as they rest on a wall is of great value in keeping them down in a screened house. 2. _Protection of the Individual._ The house should be thoroughly screened with copper-wire screens which should have 18 meshes to the inch. Mosquitoes can pass through a 15 mesh screen. Screen doors should always open outward and close automatically with spring hinges. It is almost impossible to screen a ship’s hatches effectually. Then too the screening of fan intakes and ports interferes with free circulation of air, thus adding to the discomfort of the heat of the tropics. As malarial mosquitoes bite chiefly toward evening one should not expose himself after sunset. Houses should be far removed from native habitations. Mosquitoes prefer the lower floors of a house so that the upper stories are preferable for sleeping. Mosquito nets at night, with protection by veils for the face or coverings for the hands and ankles, when going out of the house, are well-known measures. It is stated that Emin Pascha always carried a mosquito net and never suffered from malaria. He thought that the cause of malaria was too large to go through the net. Even when mosquito nets are intact and well tucked in there is the weak point that a person sleeping on a narrow cot is apt to put his arm or leg against the net, in which case the mosquitoes readily bite the skin presenting at the open spaces. Oil of citronella is often used to keep away mosquitoes. Brooks recommends Neal’s method. In this daub a solution of 1 ounce Epsom salts in 10 ounces of water on the exposed parts and allow to dry. Application of certain pine products used as mange cures will keep away mosquitoes. 3. _Quinine Prophylaxis._