CONDITIONS INFLUENCING PREVALENCE 193 



amount brought down by perennial canals is comparatively 

 insignificant. 



It is, I believe, this staunching action of silt that renders 

 places liable to flooding so notoriously malarious. The 

 actual floodings are too occasional and temporary to exercise 

 much direct influence ; but the waterproofing of the surface 

 enormously favours the production of fairly permanent 

 puddles. The obvious remedy lies in the digging into the 

 soil of some more coarsely grained material, and in many 

 cases this would be not only practicable, but actually bene- 

 ficial to cultivation, for soil of this kind is necessarily im- 

 pervious not only to water but to air, and is therefore 

 unfavourable to the growth of plants. Not unfrequently the 

 thickness of this silt-choked layer of soil is but small, and 

 is immediately underlaid by coarse, pervious sand, so that 

 there is no need to bring material from a distance, and 

 that all that is required is digging, or even ploughing, to 

 a sufficient depth to break up the thin impervious super- 

 ficial layer, and to mix with it the abundant more coarsely 

 grained substratum. 



Whatever the system employed, however, the extent to 

 which cultivation, whether irrigated or otherwise, favours 

 malaria depends almost entirely on the habits of the 

 cultivators. Where the agriculturist is neat and systematic 

 in his operations, and especially when he is anxious to 

 utilise every available foot of land, cultivation is harmless 

 because the waste of space and of water implied by the 

 presence of puddles is carefully avoided, while on the other 

 hand untidy cultivation necessarily spells opportunity for the 

 entire race of Mosquitoes. 



It is for this reason that garden cultivation is as a rule 

 harmless, unless there be some special feature in the plan 

 of operations that provides the necessary collections of 

 water in some other way, and such is unfortunately the case 

 with the gardens that commonly surround our bungalows 

 in Northern India. 



For the greater part of the year artificial watering is an 

 absolute necessity, and the plan employed is usually not 

 irrigation in the usual sense of the word, but watering by 

 13 



