240 PARASITISM 



better tluni eureT Let us agree to destroy the inter- 

 mediate hosts, the middleman as it were, the worthless 

 insect, whether a mosquito, flea, or a fly. 



Now drainage strikes at the source of the mosquito. 

 Drainage has, in fact, been the agent, from the 

 beginning— that is, since man began to till the ground, 

 and to live in towns — whicli has been employed to 

 remove excessive or stagnant water ; a condition which 

 would have impeded proper cultivation and the ex- 

 tension of towns and villages. It is very largely for 

 this reason that in Europe, and in the United States, 

 endemic malaria has ceased to exist. It is true that 

 all the Anopheles in these countries hav^e not been 

 killed ; nevertheless they have been driven out of the 

 centres of population, and that suffices to turn the 

 scale against them. For it must not be forgotten that 

 in a war against insects, man does not stand alone ; he 

 has numerous allies in the form of the natural enemies 

 of insects, so that when once the campaign is started, 

 it is remarkable how soon the insect appears to 

 diminish and the disease to vanish. The task, there- 

 fore, of insect-extermination is not the insurmountable 

 or impracticable one that some people imagine. This 

 method has also the immense biological advantage 

 that not only does it protect man, but it also 

 tends to prevent otlier animals becoming infected, 

 thereby very materially reducing the total number of 

 animal reser\oirs. \\\ brief, elimination of the trans- 

 mitting or intermediate host, whether a mosquito, 

 flea, bug, or fly, is the rational natural method of 

 prophylaxis. The use of drugs must always be limited 



