58 PLAN OF CAMPAIGN AGAINST THE MOSQUITO 



to form a film, which then prevents the larvae from 

 coming to the surface to breathe. It is usual to 

 employ this method for cisterns which are difficult of 

 screening with wire gauze. 



The method of larvie destruction which strikes 

 at the root of the problem is, of course, drainage, i.e. 

 getting rid altogether of the water in which the larvae 

 develop. Drainage is carried out in many ways. 



Road drainage. — Roads should be constructed with 



■proper falls, free from puddles, with side drains of 



concrete or stone, which must be kept scrupulously 



clean, so that it is impossible for water to stagnate in 



them. 



Streams and rivulets in valleys, gullies, and cuttings 

 should be trained so that the edges are sharp, the 

 simplest way being to concrete them. 



River canals and pond banks must be cut sharply, 

 so that there are no small bays where water can rest. 

 Regular flushing of, drains should be insisted upon. 

 Yards ought to be constructed with proper falls to 

 the street drain. 



There is an immense field for successful antimosquito 

 work in drainage. The guiding principle being to 

 prevent storm water or water from any source remain- 

 ing stagnant in pools or in any receptacles. 



Great attention must be paid to drains to see that 

 they do not sag, also to house gutters for the same 

 reason, also to the xcatcr-holding plants, like the 

 Bromeliacecc or wild pines. It is not easy at first 

 to appreciate the large water-holding capacity of the 

 wild pine. In the Port of Spain — Trinidad — my 



