PART I.] Influence of '' Laterite'' Soil on Cholera-prevalence. 247 



of the " endemic " area in cholera maps — we find a tendency for the disease to push 

 on into June. 



Midnapore, again, deviates somewhat from the lother stations in this group, in 

 that it shows a high cholera rate in June, and in other ways. The bulk of the 

 June cases, which constitute this excess, occurred in 1857 and 1860 : 103 cases in 

 the former year, and 140 in the latter. It may be remarked in passing, that, 

 unlike the rest of the stations in the list, Midnapore, together with a great portion 

 of the district in which it lies, is situate on laterite soil. Indeed, it is perhaps not 

 quite correct to imply that the disease is endemic in this particular town, as it would 

 appear that occasionally it is absolutely free of it. 



There is an idea prevalent that cholera is less liable to occur in lateritic 

 districts than in others in India. We do not know what grounds exist for the 

 supposition, but it is a matter deserving of the attention of those who have 

 opportunities for judging. This peculiar soil — a compound of clay and oxide of iron 

 — is very porous, and possesses the property of hardening on exposure to the atmo- 

 sphere. In some parts of India it is very general, being spread out in sheets over 

 the surface, from a few inches to many feet in thickness.* 



With regard to the particular month in which cholera may be said to manifest 

 itself in its average intensity at these stations, it is found that no marked uniformity 

 exists, the local entourage of each station being, as may readily be supposed, 

 sufficiently distinct to modify the seasonal prevalence of the disease to this extent. 

 On the other hand, to attempt to ascertain this by taking the mean of the monthly 

 cases of the stations forming the group could hardly be deemed as sufficiently 

 approximate to the truth to warrant any marked deviation from the usual mode of 

 tabulating seasonal occurrences. Each station would require to be taken by itself, as 

 was undertaken with regard to Calcutta. 



Assuming the end of September to correspond with the average termination of 

 the rains, October may be conveniently taken as the commencement of a season; and 

 as more than 50 per cent, of the annual rainfall of this group of stations falls within 

 four months. May to September, the year might even be divided into the wet and 

 the, comparatively, dry season. On the whole, however, we have deemed it convenient 

 to adopt the tri-seasonal divisions, commonly adopted by meteorologists in this 

 country, viz., January to May, June to September, and October to December, but 

 taking the last-named division as the first, instead of the third. 



Omitting the statistics of the general population of Calcutta from our calculations, 



* Whilst these pages were passing through the press, we consulted the Civil Surgeon of this station 

 (Dr. R. J. Mathew) regarding what appeared to us to be some inconsistencies in the course taken by the 

 water-level, judging from the returns. The following extract from Ur. Mathew's reply is very interesting : 

 " Midnapore was an unfortunate station to select for such observations, inasmuch as, owing to the porosity 

 of the sub-soil and lower strata, two-thirds of the wells in the place are dry for nearly half the year, and 

 during the rains a well will fill in one night, and in two days after, should there be no rain, will be found 

 half empty." 



