27 



I do not recommend this procedure. The fact is that 

 the large majority of the puddles can each be obliterated, 

 temporarily at least, by a stroke or two of the pick and 

 shovel, and a few basket loads of gravel. It is necessary 

 only to set the gang at work straight away, and they will 

 probably clear out most of the stagnant water in a few 

 months. A formal drainage scheme had better be aban- 

 doned until simpler methods have at least been tried and 

 have failed. 



But in order to obtain the best results the superin- 

 tendent must proceed with method. He should be guided 

 by the following important principle : Attack first those 

 collections of water the obliteration of which will remove 

 the largest number of mosquitoes for the least amount of 

 money. Thus, it is quite useless to drain stagnant water 

 simply because it is stagnant water. The superintendent 

 should first assure himself that it does actually contain 

 larvae, and, better, that it constantly contains them. As 

 already mentioned, some pools are too large, others are too 

 small, and others are subject to scouring ; and, though 

 these conditions often change at certain seasons, when, for 

 instance, large pools dry up, yet some pools appear to be 

 habitually unsuited to the larvae.* It is useless to spend 

 much money over these. Again, it is not advisable to attack 

 without discrimination even the pools which do contain 

 larvae. Some contain many more larvae than others do ; 

 and, in my experience, while larvae do occur in some con- 

 siderable bodies of water, such as marshes or ponds, they 



* On revisiting Freetown after two years' absence, I was struck by finding 

 the larvae in exactly the same pools, however small ; while other pools pre- 

 viously negative, remained negative. The most insignificant puddles seem to 

 be much more permanent than would be thought possible, and year after year 

 fill up with rain and breed mosquitoes. 



