(c) Destruction of mosquito breeding places, by: i. Drainage (Figs. 76, 77).
2. Training of water courses, or by 3. Filling.
Attention should be paid to all depressions both natural and artificial, and of either stagnant or running water within one half mile radius of the area where control operations are being prosecuted.
The planting of eucalyptus trees in swampy wet areas that for one reason or another cannot be drained, has been recom mended, but their value for this purpose is undetermined. They apparently accelerate the evaporation of the swamp water.
(d) Destruction of Mosquito Two methods may be used.
I. The application of a thin iridescent film of oil to the sur face of water areas it is not feasible to drain, at least after every rain. The oil is either sprayed from knapsack sprays, or fed by drip cans. The latter are only adapted to streams or ditches conveying running water. Crude oil is best (Figs. 74, 75).
3. Stocking swamps and pools with species of fish that are predatory upon mosquito larva. The Public Health Service is introducing the employment of the top minnow, Gantbusia affinis, for this purpose.
2. The application of solutions having a lethal action on the larvx, such as the "Larvicide" of Darling. This is prepared from crude carbolic acid of a sp. gr. not greater than 0.97 and containing not less than 3o per cent. tar acids. One hundred and fifty gallons of the phenol are heated in a tank and to this 200 pounds of finely crushed and sifted rosin are added and also 3o pounds of caustic soda dissolved in 6 gallons of water. This is well mixed. For use a i:5 dilution in water is made. This is sprayed on water accumulations until the water has a thin milky opalescence (about :5000).
In applying either oil or larvacide especial attention must be given to the margins and weedy places in the streams and pools. Depending upon the degree of agitation and the amount of fresh water introduced by rain, etc., repeated application of these will have to be made at irregular intervals.
(e) Destruction of Adult Mosquitoes: I. Adult mosquitoes may be naturally destroyed by the encouragement of various natural predaceous enemies, such as bats, dragon flies, etc. These alone, however, will not suffice.
2. Swatting or trapping of adult mosquitoes in dwellings: They prefer to hide in dark corners during the day, where patient search will soon result in their discovery. One may also
fumigate by burning pyrethrum.
(f) Exclusion of adult mosquitoes from dwellings.
Screening is the best method of accomplishing this result. A fine mesh screen of at least 19 to 20 strands per inch should be employed. All external openings should be screened, in cluding windows, doors, fireplaces, or chimneys, cracks, etc. If possible verandas or galleries should be screened, rather than to limit one's efforts to the windows and doors leading out upon them. Doors may be protected by screened vestibules if necessary. In the absence of screening bars should be pro vided for all beds.
Screening and the control of mosquito breeding on the living premises are remedies available to every householder. On the other hand, the elimination of areas of extensive breeding is an effort that requires concerted community action. The methods or combinations of methods required to meet local conditions will vary, and require the exercise of considerable judgment. The question of initial cost and maintenance costs will likely be factors that largely influence the permanency of the efforts. At Havana, Panama, Ismailia and a few other places, the importance of mosquito control to the authorities was such that expense was not considered in securing the desired result. On the other hand, the control of malaria in the southern United States is a problem that will only be solved by methods that are within the slender resources of the average rural community. The possibilities in this direction have been brilliantly demonstrated by the work of Dr. H. A. Taylor in a group of rural towns in south eastern Arkansas. In the four towns in which antimosquito measures were undertaken in 1918, there was an average reduction in the incidence of malaria of 89 per cent. The operations included the cutting of new drain age ditches where necessary, the recleaning and regrading of old streams and the oiling of all accumulations of water not possible to drain. This was accomplished at an average per capita cost of eighty eight cents. The work requires careful and intelligent supervision.