218 GNATS OR MOSQUITOES — CHAPTER VIII 



by a clear understanding of the conditions that favour the 

 multiplication of these troublesome insects. 



The first step is to discover the pools where they breed 

 and the seasons at which they do so. This done, we have 

 to consider why these pools exist, and if possible to remove 

 the cause. Unfortunately in many cases the breeding 

 places, although small, are so numerous that the task of 

 dealing with them in detail is almost hopeless, and would 

 involve heavy and continuous expense. This may be due to 

 the character of the soil or to waterlogging, and in such cases 

 only extensive drainage works, surface and deep, can be 

 expected to afford any permanent benefit. As a rule it is too 

 costly to attempt anything but surface drainage, and even 

 this is by no means an easy matter, for unless the drains be 

 most carefully levelled and paved, they generally during the 

 rains become chains of small puddles, which form the 

 favourite nurseries for the noxious "dapple-wing" Mos- 

 quitoes. But the paving of drains on any adequate scale 

 is a most costly business, and except in closely populated 

 municipal areas out of the question on the score of expense. 

 In most cases, therefore, they are better restricted to a few 

 deep cuttings, and to straightening and clearing the natural 

 outfalls, for I am convinced that the multiplication of what 

 are called in India " kachcha " drains, i.e., shallow unpaved 

 gutters, does more harm than good, and that in canton- 

 ments and in other places where sickliness is so costly to 

 the tax-payer as to justify any reasonable expense on sanita- 

 tion, it would be better to systematically drain the area by 

 means of agricultural " subsoil " drains. As already pointed 

 out, it is a misnomer to speak of these by their usual name, 

 as they are placed immediately beneath the surface, and so 

 cannot directly affect the level of the subsoil water, and 

 they really drain only the surface ; but as its contour 

 remains unaltered they cannot lead to the production of 

 puddles in the same way as mere open cuttings in the soil. 

 Deep cuttings, on the other hand, though equally irregular, 

 do not for some reason so often harbour Anopheles larvas. 

 It may be that this is because the water is hidden from the 

 female Mosquitoes when seeking for a place wherein to lay 



