202 SLEEPING SICKNESS, FLIES, AND DISEASE 



bush along the rivers ; a strip about 30 j'ards wide 

 extending from the river-bank is tlie usual breeding 

 zone ; breeding appears not to extend to any marked 

 degi'ee beyond this distance. 



The larval or pupa stage evidently requires shade 

 and to be protected from the direct sun-rays, hence 

 tlie fly chooses the shaded light sandy humus of the 

 bush in which to deposit her pupae. Therefore, as a 

 first step in prophylaxis, it is necessary to destroy 

 the ground bush, to burn it for a depth of about 30 

 yards from the river-bank. 



It is not necessary to cut down forests any more 

 than it is necessary to drain lakes and run rivers dry 

 in antimalarial operations. All that is essential is to 

 go for the chief breeding grounds around man and to 

 let the forests take care of themselves. 



The reason is precisely similar to that which we 

 fully discussed under malaria and yellow fever. We 

 cannot attempt the impossible, and it is totally un- 

 necessary ; the object is to protect man in his villages 

 and towns and camps and along his trade routes, and 

 this can be done. It is, as we have so often emphasised, 

 a question of protecting man against his innumerable 

 insect surroundings. In practice this has been found to 

 be perfectly feasible, as easy as preventing the keeping 

 of stagnant water in and around houses in yellow 

 fever countries or getting rid of pools and anopheline 

 breedin<2f ffroimds around tlie houses in malaria 

 countries, or destroying cover for rats in seaport towns. 



What is therefore now done is to burn the ground 

 busli along the margins of rivers and ponds and around 



