CONDITIONS INFLUENCING PREVALENCE 177 



of the spongy soil as it drinks in the rains still leaves the 

 surface irregular, this soil is peculiarly favourable to the 

 multiplication of the species as long as the wet season lasts, 

 so that the physical characteristics of this sort of soil 

 necessarily are such as to favour greatly the development 

 of malaria for this short and limited period ; and as a 

 matter of fact, the seasonal incidence of malaria corres- 

 ponds well with these facts, as taken altogether, such sites 

 are fairly healthy, though malaria is rife and wide-spread 

 while it lasts. 



Owing to the instability of such a foundation the con- 

 struction of permanent works of all kinds is a matter of the 

 greatest difficulty, and hence the surface drainage of towns 

 is always costly, and even when most carefully designed 

 requires continual regrading. 



Below the black soil there is commonly, especially in 

 Kathiawar, a stratum of limestone, locally known as 

 moram (miliolite) intervening between it and the subsoil 

 water, which, though not very dense, is yet sufficiently 

 effective in holding up the surface moisture. 



It is doubtful if even subsoil drainage would be of any 

 great use in combating malaria in land of this description, 

 as the peculiarity of this soil is that it dries rather by 

 evaporation from above than by the draining away of its 

 moisture from below, and it is obvious that under such 

 circumstances works of this sort would be not only expen- 

 sive, but probably ineffective. 



With a highly civilised population it is possible that 

 some good might be effected by the systematic destruction 

 of the adult insects during the dry season, as the climate 

 and general characters of the country are such as to render 

 the shelter of houses almost indispensable to the mainten- 

 ance of the species ; but under existing circumstances this 

 appears one of those cases in which the free distribution of 

 quinine and the popularisation of its use can alone effect 

 much benefit, and is therefore the more fortunate that the 

 same physical peculiarities that so favour the development 

 of malaria for three or four months of the year also limit 

 its duration. 

 12 



