CONDITIONS INFLUENCING PREVALENCE 169 



For those who believe in the agency of the Mosquito 

 in the propagation of malaria, the explanation of this un- 

 expected and undesired result of modern sanitary enterprise 

 is not difficult. 



In by far the majority of cases no attempt at improved 

 surface drainage has accompanied the spread of the water- 



Financial tightness has necessitated that the essentials 

 of sanitary reform should be taken in hand one by one ; 

 and the effort to introduce a pure water-supply has so 

 exhausted the resources of each municipality in which it 

 has been carried out, that the proportion of cases in which 

 the engineers have been able to so place their hydrants as 

 to secure a ready flowing away of waste water has been 

 perforce a very small one, and the result has been that often, 

 each hydrant is the source of a string of puddles of con- 

 stantly renewed, fresh cool water, and not unfrequently so 

 placed as to be the greater part of the day in the shadow of 

 tall buildings. In pools so fed and situated Anopheles larvae 

 may be found at times of the year, when but for the 

 hydrants, they would be rare as the dodo ; for these larvae 

 do not appear to be able to develop in water as hot as that 

 of the ordinary stagnant pool or tank in the hot dry weather. 

 At any rate it is only in such exceptionally conditioned 

 water that Anopheles larvae can be found in the N.W. 

 provinces in March and April, for the ordinary garden tanks, 

 which in the rains will harbour large numbers, are then full 

 of Culex larvae only. In this way a piped water-supply 

 extends the period of possible infections over several months, 

 which ordinarily yield but few fresh cases. 



As even when confined to its normal times and seasons 

 malaria is responsible for a larger share of the total mor- 

 tality than any other disease, the above explanation appears 

 to me to adequately explain the apparent failure of pure 

 water-supplies to improve the general health. 



It is obvious, however, that the increased sickliness and 

 therefore presumably malariousness of these places are an 

 indirect result only of the introduction of a water-supply ; as 

 to the direct connection of which with malaria there exists 

 no tittle of proof. 



