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indeed probable, if not certain, that if the work of destruc- 

 tion be carried out over a considerable area, long, thoroughly, 

 and persistently, the mosquitoes will end by being vastly 

 reduced in that area (unfortunately the experiment has 

 never been thoroughly made) ; but the same result can be 

 obtained more permanently, and in the end probably more 

 economically, by obliterating the breeding places them- 

 selves. 



Nevertheless, while the other work is in progress it will 

 do no harm to destroy larvae wherever they are met with 

 which can be done either by the workmen in the course of 

 their work, or by special men employed for the purpose. 

 Indeed in some places, such as those just referred to, namely, 

 collections of water in use for drinking, washing, and 

 irrigation purposes, it is often impossible to drain at all, 

 and the superintendent must fall back upon destruction of 

 the larvae. 



Numerous means of destruction have been suggested 

 such as the introduction of fish, and of many chemical 

 poisons or substances inimical to the larvae. Fish, tadpoles, 

 some kinds of beetles, and other animals do eat larvae ; 

 but, unfortunately, they cannot always be introduced ; and 

 even if they are introduced, it is evident that their efforts 

 will not always be successful, since we often find living 

 larvae in the same pools with them. It is much the same 

 with chemical poisons. Waters which can be poisoned are 

 those which are not required, and which had, therefore, 

 better be drained away at once. Moreover, few poisons 

 are effective against larvae unless concentrated ; and then 

 most of them become dangerous, inasmuch as children and 

 cattle may suffer from our well-meant zeal. I have long 

 wished to find an ideal poison for mosquito larvae. It 



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