ENTOMOLOGY

868 SANITARY ENTOMOLOGYbe taken against flea bites. Workers should be provideJ with closelyfittingclothes and leggings and certain other methods of body isolationas discussed in a subsequent paragraph.When operating in regions where plague is suspected, it is also importantto choose locations for troops which are apt to be free fromrats. The billeting of men in old buildings, warehouses, barns, etc., shouldunder such conditions be entirely avoided.Control of Hosts.---.To kpep down heavy infestations of those speciesof fleas which a~e annoying to men and animals, one of the essential steps.is to exercise control over the hosts. Of course, this principle is involvedin the elimination of rats and squirrels in plague areas. When alliinfestationis encountered, the first thing that should be inquired into is thepossible hosts and their haunts. Usually the main trouble can be tracedto the sleeping places of dogs, cats, hogs, or to hen houses, or spacesbeneath houses and barns frequented by poultry. In the case of thehuman :flea the infestation may be more or less general over the' premises,but there are nearly always centers where they are concentrated andoften these are associated with pet animals. When the principal breedingplaces have been located the hosts should be destroyed if possible, orfreed from adult fleas, and kept under control. A definite sleepingplace should always be provided for dogs and cats, and these may bekept free from fleas, after treatment, by cleaning out the beds regularlyand spraying with coal tar disinfectant. The host animals may be freedof fleas by washing them thoroughly in a S per cent solution of creolinand water, or by using Ilny other standard saponified creosote compound.Kerosene emulsion made according to the formula: One pound soap, twogallons kerosene, one gallon water, reduced one to nine, is also very effective.In the case of cats these substances must be washed out of the furwith warm water and soap shortly after treatment to avoid burning ofthe skin. 2"There premises are heavily infested with adults it is 6rst necessary todestroy this stage and this may be accomplished by fumigation, if thebuilding is fairly tight, either with hydrocyanic gas, five ounces cyanideper thousand cubic feet; or by burning sulphur at the rate of four poundsper thousand cubic feet. As has been pointed out, many adults remainquiet in pupa cases or may be buried in sand or cracks where they aresomewhat protected from the effects of the gas. In destroying the immaturestages we can take advantage of the destructive effect of extremes inmoisture or dryness. Where complete flooding of infested areas is feasible,this has been known to accomplish the destruction of all stages. In othercases, loose boards and trash should be removed and burned and the• Powdered derris has been found very efficacious in destroying fleas on animals.One grain scattered in the hair of a do~ will kill all fleas present.