250 TROPICAL MEDICINE AND HYGIENE 



sites, it will often be found better to abandon the 

 station than to attempt to render it healthy. A suitable 

 site is one in which there is natural drainage or in which 

 there is sufficient slope to allow of easy drainage. Small 

 streams and springs are sources of danger. If a settle- 

 ment be made on a river the side selected should be 

 that where there are no shallow shoaling edges ; these 

 are much more liable to be overgrown and the current 

 is slacker. In the selection of sites for settlements, 

 marshes or low-lying ground must be avoided and any 

 site in proximity to such places. The effect of culti- 

 vation is twofold. In the first place, the clearing of the 

 ground and the removal of dense jungle renders the air 

 drier and admits much more sunlight. Clearing alone 

 will suffice for the extirpation of some mosquitoes : 

 those that frequent jungle, which are mainly sEdina, but 

 in a few instances dangerous Anophelina. Clearing, if 

 thorough as regards the low jungle, will cause a great 

 diminution in the number of these jungle mosquitoes or 

 their complete disappearance, even if the tall trees are left. 

 On the other hand, if suitable breeding-places are left, such 

 as sedgy streams, other mosquitoes may become much 

 more abundant, and these may include dangerous anophe- 

 lines, such as M. willmori, N. christopliersi and M. culici- 

 facies in Asia, or M.funesta in Africa, or C. argyrotarsus in 

 America. Clearing without drainage, therefore, may sub- 

 stitute one dangerous mosquito for another, though, on 

 the whole, it is beneficial, as the exposed ground dries 

 more readily in dry weather and is more likely to be 

 thoroughly flushed in heavy rains than uncleared ground. 

 If combined with drainage, and if the drains are kept 

 clear, or even moderately clear and free from sedges, it 

 is usually effective. The better the drainage required for 

 the special form of cultivation, the more will the healthi- 

 ness of the district be improved. Rubber plantations 

 require deep drainage, and the only breeding places pos- 

 sible in such a plantation are in the drains or in the 

 areas beyond the plantation into which the water may 

 be discharged. 



