As already mentioned, the number and nature of the 

 breeding pools depend greatly on local conditions. Free- 

 town, Sierra Leone, contains perhaps an excessive number 

 of pools. It was indeed partly for this reason that it was 

 selected for the first formal campaign against mosquitoes, 

 because success in its case would demonstrate the possibility 

 of success in more favoured places. In Freetown there is 

 a great rainfall (160 inches annually), and the ground, 

 though hilly, is such that water collects in many spots. 

 Even here, however, the Anopheles pools are not without 

 limit, and a gang of twenty to forty men has been able to 

 produce marked effects in so short a period as two months 

 (vide Appendix). In my experience, most other towns will 

 be easier to deal with than Freetown is, because they 

 possess either a less humid climate or a more absorbent 

 soil. In many localities, indeed, the breeding places will 

 be found to be very few. 



Much effect will be often produced in the dry season, 

 when the pools are necessarily small in number and the 

 larvae are concentrated. In the rains they spread them- 

 selves more widely of course. 



Perhaps the principal difficulty in dealing with Anopheles 

 lies in the fact that they often breed in waters which, being 

 required for drinking, washing, and irrigation purposes, can- 

 not be drained away. Here the superintendent must be 

 guided by his own common sense. It is generally, perhaps 

 always, possible greatly to limit the number of such waters 

 by closing those which are not really needed. The rest 

 must be dealt with by cleansing from weeds, deepening, 

 banking in, covering, or by persistent oiling. In all tropical 

 towns, natives are very fond of digging holes and banking 

 up surface drains. The local government ought to set its 



