"96 Capt. L. Rogers — Malaria North of Calcutta, [July, 



found on either side of the railway, although not very near it, there 

 was no marked or constant difference in the ground water levels on 

 either side of the railway. The dijffierences in the spleen rates in thid 

 tract of country cannot, then, be explained on any theory of water- 

 logging, or interference with drainage by railways or roads, although 

 the natural drainage of places is certainly bad, as in North Dum- 

 Dum. 



Again, it might be thought that the lower rate in the western parts 

 might be due to greater density of population, and consequently less 

 fever breeding grounds for the anopheles mosquitos. "With regard to 

 the former it may be pointed out that there was practically no difference 

 in the spleen rate of the densely populated western portion of Manik- 

 toUa and the very sparsely populated and somewhat more water-logged 

 eastern part of the same place, both having a filtered water supply, 

 and other similar instances could be given, Further the great differ- 

 ences in the spleen rates of the contiguous wards of the same munici- 

 palities in which every condition except the water supply are precisely 

 similar, which have already been detailed, cannot be explained on any 

 theory of varying density of population, or of mosquito breeding 

 grounds. 



Distribution of the Anopheles Mosquitos. 



The question of the relationship of the anopheles mosqf^itos to the 

 prevalence of malaria remains to be considered. It must now be taken 

 as proved that malaria may be communicated to man through the bites 

 of mosquitos which have some days previously bitten another case of 

 malaria, but it still remains to be proved whether this is the only or 

 even the most common cause by which this protean disease is communi- 

 cated. The point is one of the utmost importance to Bengal, one of the 

 principal homes of malaria, for if the disease is only communicated by 

 the bites of these tiny pests, and, they only breed in certain small 

 pools, namely, those which are too small to harbour fish, yet not so 

 small as to dry up in a day or two, as Major Ross states is the case, 

 then by searching out these breeding grounds and destroying the 

 larvae in the pools we may hope with Ross to at least rid towns or 

 small areas of malaria. Unfortunately I have not been able to confirm 

 these last statements of Ross, for both at Grobardanga and at Manik- 

 tolla, which are at the extreme of the tract of country under observa- 

 tion, I easily found numerous anopheles larvae both in tanks and in 

 smaller pools all of which contained very numerous fish. As it was 

 impossible to minutely examine 100 square miles or so of this airea 

 I determined to map out and closely search all the pools and tanks in 



