248 TROPICAL MEDICINE AND HYGIENE 



ample to render such places healthy, if care is taken that 

 he drains themselves are not suitable for breeding places. 

 Where the malaria- carrying anopheles are mainly breeders 

 in such drains, it is more effective to use pipe drains, or 

 other forms of curved drains, and though more expensive 

 at first, as they require less constant supervision and a 

 smaller gradient, in the long run they are more economical 

 as well as more effective. 



The history of plantations in the past is instructive. 

 In the early history there is a serious amount of malaria 

 before the drainage is complete ; whilst the estate is 

 flourishing and kept in good order no malaria or very 

 little ; but when the estates are abandoned or neglected, 

 and the drains are sedge grown, blocked or partly broken 

 down, they become intensely malarial for any remaining 

 inhabitants. 



The class of drains employed in any place is mainly 

 dependent upon the amount of money that can be 

 devoted to the purpose. Earth drains suffice, but require 

 much continued expenditure in upkeep and repairs, whilst 

 constant supervision is required. Wherever there is 

 much flushing or scouring, brick or cement open drains 

 are absolutely essential. 



All open drains should be V-shaped in section, so that 

 a small amount of water will suffice to flush them and 

 little water can accumulate in the narrow bottom of the 

 drains. The large drains should be similar in section, 

 but the bottoms may be flat or, better, rounded. Half 

 pipes or stone pipe inverts make excellent bottoms for 

 such drains. 



It is always advisable to keep a settlement or village 

 clear of jungle and undergrowth. Such growth gives 

 shelter to mosquitoes in the daytime, prevents the drying 

 of the surface, and often leads to blockage of drains and 

 interference with natural drainage. 



As temporary methods the destruction of larvae by 

 larvicides is of great use, but should not be relied on 

 for permanent purposes. Crude petroleum or other oils 



