In almost all dwellings of the better class of tenants there are fixtures and fabrics which will be injured by the fumes of sulphur. Therefore, in this class of buildings we generally used pyrethrum. For fumigating in this same class of buildings where pyrethrum was used we found a mixture of camphor and carbolic acid, one part of camphor to three of carbolic acid, very useful. This should be placed in a tin dish and vaporized with a spirit lamp. The same procedure should be observed as a precaution against fire as is taken with sulphur. The mixture when vaporized gives off dense white fumes which kill the mosquito. Generally, where care has to be taken for fear of injuring fixtures and fabrics, this mixture is preferable to pyrethrum. Pyrethrum should be used at the rate of one pound to the thousand cubic feet, and the camphor mixture at the rate of an ounce for the same space. In Havana we had to deal with cigar manufactories and tobacco storehouses on a large scale. Here we could use neither sulphur, pyrethrum, nor the camphor mixture, as they all affected the delicate flavor of the tobacco. At first we used to move all tobacco out of a building to be fumigated. This was very laborious and added largely to the cost of fumigation and also tended to drive out from the building the infected mosquitoes before they had been reached by fumigation. Mr. Joseph Le Prince, who was in charge of this work, after much experimenting found that the fumes from tobacco stems did not hurt the flavor of tobacco, and were almost as deadly to the mosquito as was sulphur. We could therefore fumigate with this material buildings where tobacco was stored without injury to the tobacco. The stems were a waste product in cigar manufacturing, and could be obtained in large quantities at little cost. They should be used at the rate of two pounds to the thousand cubic feet, and with the same precautions against fire as are taken in other cases. Formalin we found useless. It has apparently little effect upon insect life. From our general knowledge of the life history of all species of mosquitoes, we knew they had to spend eight or nine days in a larval stage, and that while in this larval stage they lived in water. Therefore, collections of water were necessary for the development of the mosquito. The stegomyia mosquito we knew preferred clear, clean water, such as is supplied by the various collections of rain water needed for domestic purposes. The city of Havana had pipe water over only a small portion of its area. By far the larger portion of the population obtained its water supply from rain water stored in cisterns, tanks and receptacles of all kinds. We resolved to stop mosquito-breeding in all such places.