must remember that, since in most non-insular places the 

 insects can enter from without, efforts to destroy them in- 

 dividually will never be permanently successful. On the 

 other hand, if we keep the area of operations entirely free 

 of breeding places, we shall and must reduce greatly the 

 number of insects, because, even if a few do manage to 

 effect an entry from without, these will no longer be able 

 to multiply within the area as they used to do. It is quite 

 obvious, if we think of the matter for a moment, that one 

 or two breeding places will give rise to fewer mosquitoes 

 than 100 or 1,000 breeding places would do. If, for 

 example, a given town contained 1,000 breeding places 

 producing 100,000 mosquitoes daily, we are forced to con- 

 clude that the daily production of mosquitoes would be 

 visibly reduced if all these breeding places were to be 

 obliterated. Any mosquitoes effecting an entry from with- 

 out would be so few in number, in comparison with the 

 previous swarms of insects in the town, that they would 

 scarcely be observed at all. If we consider the subject 

 then in the light of these facts, we shall be able to decide 

 upon the measure most likely to be profitable ; and this is 

 evidently that of removing all the breeding places. But 

 concurrently it will do no harm to attack the insects in- 

 dividually whenever and wherever we meet them. 



It has been a matter of serious difficulty to get people 

 to understand these ideas, simple as they are. Even when 

 the advisability of removing the breeding places has been 

 admitted, doubts as to the practicability of the measure 

 have been entertained. Now the reader will remember 

 that every new project is thought by many before it is tried 

 to be impossible. After they have been tried, new projects 

 often turn out to be not only possible but extremely easy. 



