ENTOMOLOGY

THE LIFE HISTORY AND CONTROL OF FLEAS 367being reached in August to September, the maximum being six times lessthan in April. The plague season in the districts where these observationswere made ,is from February to May, inclusive. The maximum isusually reached early i::1. May, sudden decline being experienced withthe dropping bfF in numbers of the fleas early in June.The degree of annoyance to man from fleas depends to a large extentupon the relative abundance. Thus in the southern part of the UnitedStates, while fleas are active throughout the year, they are reduced solow during the winter months that they confine their attacks largely tosmaller animals. During the spring the breeding increases rapidly andoften severe outbreaks are experienced. In the Northeastern States theseoutbreaks are more frequent during the latter part of summer and earlyfall.There is also marked correlation between the character of soil andflea ab1;lndance. Sandy land is uniformly more conducive to :flea developmentthan the heavy soils. However, soils with a large amount of humusseem al~o to favor flea' breeding. We do not expect to encounter widespreadflea abundance in black land regions, but this does not interfere\vith severe local outbreaks. -CONTROL OF FLEASThe general consideration of flea control must be governed by theconditions l1nder which one is working. When we consider regions whereplague is known certainly not to exist, little concern need be felt overthe presence of an occasional flea, and all that is necessary is to takeprecautions that they do not become annoyingly abundant. Occasionallypremises already infested may be encountered and in such cases it is necessaryto know what steps to take to reduce the numbers immediately. Onthe other hand, in regions where the presence of plague may be suspected,the elimination of all fleas is desirable, and one must give attention tothe scattered fleas as well as the heavy infestations. Of course in suchsituations the prime move should be against the rats which act as hostsfor both the plague bacillus and the fleas which carry it. In cases wherethe plague has become established in rural districts among groundsquirrels or other native roden:ts, their destruction also requires attention.The procedure in such cases must necessarily be governed by the durationof occupancy of a given place. For permanent elimination ratproofingis essential. This consists in the elimination of all loosely constructedbuildings and the concreting of floors, basements and wharves.While the rat-proofing is going on war should be waged against therats by poisoning, shooting, and trapping. Where plague is -known to'exist in a city or village being cleared of rats, every precaution should