For carrying into execution the orders pertaining to mosquito work the city was divided into eight districts, each district in charge of a mosquito inspector. A great deal of stegomyia breeding went on in the interior of the dwellings. Every family had an earthen vessel in which drinking-water was kept for daily use. This always had larvæ in it. It was the inspector’s duty to empty this vessel, point out the larvæ to the housekeeper, and explain that if the vessel were emptied once a day and the larvæ washed out, mosquito development could not occur. All sorts of vessels in a house which might contain water had to be considered as possible breeding-places for mosquitoes. Every housekeeper in Havana, when we started work there, had a number of breeding-places for mosquitoes in her domestic establishment. Among these may be mentioned flower-pots in which a little too much water had been used; cans filled with water, in which the legs of tables had been placed as a protection against ants, etc. Each mosquito inspector had with him five men, and one of these men carried a sufficient amount of oil to pour upon any pools or puddles about the premises that might need oiling. They picked up old bottles and cans which might contain water and become breeding-places, and generally looked after the yards. The district inspector, at the same time, made a general report on the premises in writing, and on this report the owner was called to account if unsanitary conditions were found existing. Next to cisterns and water barrels, roof gutters were found to be the most general breeding-places for the stegomyia mosquitoes. Leaves and trash fall upon the roofs, are washed into the gutters, and these make little dams behind which water collects and remains after the rain has ceased. At other times the gutter sags and thus forms a collection of water. In the tropics you can always count upon roof gutters as being places for mosquito-breeding, and being inaccessible and difficult to inspect, such breeding-places are seldom disturbed. During its larval stage the mosquito lives entirely in water, but has to come to the surface frequently for the purpose of getting air. This necessity is seized upon by man for the purpose of destroying the larvæ. If kerosene oil is poured upon the water, it spreads in a very thin film over the surface. Now when the larvæ rise to breathe, the oil gets into their breathing-tubes when they attempt to force them through the thin film of oil spread over the surface of the water. This suffocates and kills the insect and is very effective.