290 Cholera in Relation to Certain Physical Phenomena. [part i. 



support from them. According to it, maximum prevalence ought to occur at that 

 period of the year when the meteorological conditions are of a nature calculated to 

 facilitate the entrance into the drinking water of materials derived from the bodies 

 of those suffering from the disease, and specially of the materials of the intestinal 

 excretions. The period during which most material is washed into the tanks and 

 other bodies of water, which, until quite recently, constituted the universal sources 

 of drinking water in Calcutta, is, that of those months in which the rainfall is 

 greatest and characterised by the greatest heaviness of individual falls. These months 

 are June, July, August and September; but the first of these is a month of low 

 medium, while the three others are months of minimum prevalence. With reference 

 to the latter three months, it may be argued, that although the inwash of materials 

 is then great, the inwash of the specific material producing cholera is not so, as 

 it has been in great part removed from the surface of the soil by previous rainfall 

 and that the influence of what still remains to be introduced is neutralised by the 

 coincident dilution of the sources of drinking water. 



This argument is, however, quite inapplicable to the phenomena of June. At 

 this time there has been no sufficient previous rainfall to remove the specific material 

 from the soil surface, or to dilute the water supply ; and yet the abundant and 

 violent rainfall of June is accompanied by a great decrease in prevalence. Equally 

 inexplicable on this theory are the phenomena presented by May and November. In 

 May the amount of specific material ready for introduction must be at a maximum, 

 for the preceding months are those in which the number of cases of the disease — 

 the number of assumed factories of the poison — far exceeds that present at any other 

 time of the year. In May, too, both the total rainfall and the heaviness of individual 

 falls are, on an average, higher than in April ; and yet at this very time, when 

 everything, according to the theory, provides for excessive increase in prevalence, 

 there is, on the contrary, a marked decrease. We have here an instance of decrease 

 where the theory requires increase, and the phenomena of November furnish an 

 example of an exactly opposite nature — furnish an instance of meteorological conditions 

 which, according to the water theory, ought to ensure decrease, but which, in fact, 

 coincide with marked increase. When we compare the rainfall of November with 

 that of October, we find that, in so far as provision of means securing inwash of 

 materials is concerned, the latter month occupies a much higher place than the 

 former ; and yet the virtually rainless November shows a great increase in prevalence 

 when compared with October. 



3rc?. — The theory which regards the degree of impurity of the drinking water as 

 the essential determinant of the prevalence of cholera. According to this theory, the 

 periodic fluctuations in the prevalence of cholera in a locality in which the disease is 

 endemic are dependent on corresponding variations in the degree of impurity of the 

 water-supply. In so far as the general physical conditions of locality are concerned, 

 the degree of impurity of the water must depend on the degree to which the entrance 



