1900.] and the distribution of Anopheles Mosquitos, 475 



Conclusions. 



The general result of the inquiry has been to show that there is a 

 marked difference between the health of the riverine and more inland 

 portions of the area examined, the former being much more healthy 

 than the latter. The comparatively healthy area extends from the river 

 to the Grand Trunk Road, and in some parts to the Railway, a distance 

 varying from one to two miles. No marked or constant differences in 

 the ground water-level of the healthy and unhealthy parts has been 

 found, which could possibly account for the differences in the spleen-rate 

 noted, so that no theory of water-logging will explain them. 



The most striking exception to the rule that the areas at a distance 

 from the river bank have a high spleen-rate is that of Maniktolla, and 

 the eastern portions of Chitpore-Cossipore between the Grand Trunk 

 Road and the railway, both of which, together with the rest of the latter 

 Municipality, have the lowest spleen-rates of all. Moreover they are 

 also the most water-logged portions of the whole area, their ground 

 water-levels both in the dry and in the rainy seasons being the highest 

 met with, so that there must be some other factor to account for their 

 marked immunity from malaria. This is certainly not the absence of 

 the malaria-bearing mosquito, for it was in the first-named place that 

 they were found to be more wide-spread during the minimum fever 

 season than has hitherto been reported from any part of India. The 

 only possible factor remaining is the water-supply, and it is noteworthy 

 that these two water-logged Municipalities are the only ones which have 

 a full filtered water-supply from the same source as Calcutta itself. 

 That this good water-supply is the true explanation of their relative 

 immunity from malaria is borne out by the very low spleen-rate of certain 

 Wards of other Municipalities which have a partial filtered water-supply 

 from various Mills, together with the low rates of the "Wards of 

 Baranagar and South Dum Dum, which border on Chitpore-Cossipore, 

 from whose stand-pipes some of their inhabitants were obtaining filtered 

 water, the details of which have already been given. Finally, the 

 figures given in Table X. shows the spleen-rates among river water 

 drinkers to be nearly double, and that of tank water drinkers to be 

 nearly treble that of filtered water drinkers, strongly corroborate the 

 evidence as to the benefit to be derived from filtered water, and affords 

 a key to the whole distribution of the varrying spleen-rates, as can be 

 seen from a study of the accompanying map. Thus, Chitpore-Cossipore 

 West, which has the double advantage of a filtered water-supply and 

 close proximity to the river, so that those who do not drink filtered 

 water will for the most part take river water, has the lowest rate of 

 all, namely, 7'4 The eastern part of the same Municipality, which 



