Another popular error is that, even if we succeed in 

 destroying all mosquitoes over a given area they will swarm 

 in again from the outside immediately after the measures 

 are completed. But it should be clearly understood at once 

 that all measures for the extermination of mosquitoes must 

 be continued indefinitely, so that even if fresh insects do 

 arrive from the outside they will not have an opportunity 

 for multiplying within the given area. In other words, all 

 towns which wish to be kept free from mosquitoes must 

 determine upon, not a single effort, but a continuous one. 

 In fact, just as all towns possess a staff of sweepers for the 

 purpose of keeping its streets clean, so in the future must 

 all towns in the tropics possess a staff of persons whose 

 duty it will be to keep down these dangerous and trouble- 

 same pests. 



3. General Principles to be Followed. Suppose it 

 were required to get rid of all mosquitoes from an island 

 situated in mid-ocean. It would be possible to follow two 

 courses. First, we might set about destroying every mos- 

 quito, either in the adult or in the larval stage. If this 

 could be done with sufficient pertinacity there can be no 

 reasonable doubt that, in the end, the island would 

 become entirely free of them supposing, of course, that 

 the insects cannot enter the island from without. Another 

 method, equally promising, would consist in attacking not 

 the insects individually but their breeding places ; would 

 consist in removing every drop of stagnant water in which 

 they breed, so that, ultimately, the insects would die out 

 of themselves. 



Now in our efforts to rid a locality which is not an 

 island, we need follow only these same principles ; but we 



