PART. I.] Cholera-prevalence Most Marked in March, April, or May. 245 



(b) Prevalence of cholera according to Monthly periods in the Endemic area, and 



the mean monthly Rainfall. 



Applying the same principle to these endemic districts as was applied to 

 Calcutta, we have collected the monthly cholera returns for several years past and 

 compared them all, so far as the data available permitted, with the several 

 meteorological and allied physical conditions. It is not deemed necessary to submit 

 full details of these comparisons, as, taken together, they yielded closely similar 

 results. As in Calcutta, so in these districts generally, the most characteristic 

 physical phenomena with which the prevalence of cholera is associated all over the 

 endemic area, are indicated by the fact that at most of the stations the disease is 

 less prevalent during the height of the rains, or rather it would be, perhaps, more 

 accurate to say that it attains its maximum when the depression of the sub-soil 

 water is at its maximum, and consequently, in a general way, holds an inverse 

 relation to the proximity of the sub-soil water to the surface, so long, of course, as 

 the sub-soil water under observation is ascertained to lie over the first impermeable 

 layer. 



This is completely in accord with what all writers who have studied this subject 

 specially have asserted. Dr. Bryden (op. cit,, page 61), after describing the proximity 

 of the water to the surface in the endemic area, and pointing out that vast tracts of 

 land are annually submerged, writes : " It is with the inundation of these tracts that 

 cholera disappears, and it is with their re-appearance that cholera re-appears." 



In Table XLIII, on following page, wall be found a monthly statement of rainfall 

 and of all the cholera cases that have been registered among the European and Native 

 troops and the Prisoners in all the principal stations distributed over the area which 

 has just been referred to as furnishing meteorological phenomena and conditions of soil 

 closely resembling those observed in Calcutta. 



It will be noticed that, save in the case of Calcutta itself, no use has been 

 made of the statistics which have been collected among the general population. This 

 has been done because no sufficiently trustworthy records of vital statistics are at 

 present in existence. As the data employed refer solely to communities of average 

 uniform strength from year to year, regarding whom very accurate information is 

 recorded, and as this information extends, in nearly all cases, over a considerable 

 number of years, they suffice to indicate the time of year when cholera is most pre- 

 valent, especially when all the stations are taken together. 



Taken month by month it will be seen that the dozen stations tabulated present 

 considerable similarity. In nearly all of them it is in March, April or May that 

 cholera prevalence is most marked, more especially in such of the stations as closely 

 approximate to Calcutta in its physiography. When, however, we approach the 

 borders of this territory— as, for example, at Dinapore, a station commonly left out 



