THE LIFE HISTORY AND CONTROC OF FLEAS 367 



being reached in August to September, the maximum being six times less 

 than in April. The plague season in the districts where these observa- 

 tions were made is from February to May, inclusive. The maximum is 

 usually reached early in May, sudden decline being experienced with 

 the dropping off in numbers of the fleas early in June. 



The degree of annoyance to man from fleas depends to a large extent 

 upon the relative abundance. Thus in the southern part of the United 

 States, while fleas are active -throughout the year, they are reduced so 

 low during the winter months that they confine their attacks largely to 

 smaller animals. During the spring the breeding increases rapidly and 

 often severe outbreaks are experienced. In the Northeastern States these 

 outbreaks are more frequent during the latter part of summer and early 

 fall. 



There is also marked correlation between the character of soil and 

 flea abundance. Sandy land is uniformly more conducive to flea develop- 

 ment than the heavy soils. However, soils with a large amount of humus 

 seem also to favor flea breeding. We do not expect to encounter wide- 

 spread flea abundance in black land regions, but this does not interfere 

 with severe local outbreaks. 



CONTROL OF FLEAS 



The general consideration of flea control must be governed by the 

 conditions under which one is working. When we consider regions where 

 plague is known certainly not to exist, little concern need be felt over 

 the presence of an occasional flea, and all that is necessary is to take 

 precautions that they do not become annoyingly abundant. Occasionally 

 premises already infested may be encountered and in such cases it is neces- 

 sary to know what steps to take to reduce the numbers immediately. On 

 the other hand, in regions where the presence of plague may be suspected, 

 the elimination of all fleas is desirable, and one must give attention to 

 the scattered fleas as well as the heavy infestations. Of course in such 

 situations the prime move should be against the rats which act as hosts 

 for both the plague bacillus and the fleas which carry it. In cases where 

 the plague has become established in rural districts among ground 

 squirrels or other native rodents, their destruction also requires attention. 

 The procedure in such cases must necessarily be governed by the dura- 

 tion of occupancy of a given place. For permanent elimination rat- 

 proofing is essential. This consists in the elimination of all loosely con- 

 structed buildings and the concreting of floors, basements and wharves. 

 While the rat-proofing is going on war should be waged against the 

 rats by poisoning, shooting, and trapping. Where plague is known to' 

 exist in a city or village being cleared of rats, every precaution should 



