CONDITIONS INFLUENCING PREVALENCE 209 



that this self-raising action must have a most beneficial 

 effect by favouring surface drainage, and this affords us a 

 hint that might well be taken advantage of in planning new 

 settlements on ground reclaimed from the desert by canal 

 irrigation ; only in place of gaining the earth by honey- 

 combing the plain hard by with a network of foul tanks, the 

 spoil should be taken from carefully planned drainage cuts 

 carried along the natural lines of drainage. Surely, con- 

 sidering the vast outlay involved in the construction of a 

 great canal, it should be a good investment to spend con- 

 siderable though comparatively trifling sums to secure 

 health for the colonists who come to reap the plenty brought 

 by the fertilising water. 



Such being the conditions that influence the prevalence 

 of Mosquitoes, it may be asked whether the seasonal preva- 

 lence of these insects really corresponds with the intensity 

 of malarial disease '? On this point the figures given by Celli 

 are sufficiently convincing, but for many reasons it is difficult 

 to quote statistics of corresponding value for India, though, 

 speaking generally, no doubt can be entertained as to the 

 fact of the coincidence, or rather consequence. 



The connection is, however, of a kind that is much more 

 obvious to the working physician that to the statistician. 

 The former well knows that, in Northern India for instance, 

 his really troublesome malarial cases occur between the 

 middle of August and the end of November, and that those 

 which are admitted between January and August are mostly 

 recurrences, generally lasting only a few days, and of a 

 comparatively mild type. 



These relapses, however, go to swell the number of 

 admissions in months during which, in many parts of India 

 Anopheletes are, practically speaking, as rare as the dodo ; 

 and thus it happens that in spite of the infinite amount of 

 labour that is wasted on the statistics that lumber the 

 record rooms of our offices in India, we are still quite 

 without any really reliable information as to the seasonal 

 prevalence of malaria. 



Apart from the fact that hitherto no attempt has been 

 made to distinguish between primary and recurrent attacks, 

 14 



