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



Calcutta the range of temperature between the coldest and warmest month is 18°-5, 

 in Lahore it is 39°*6, or, stated in reference to prevalence, in Calcutta the difference 

 between the temperature of the month of maximum cholera and the coldest month 

 is 13°-8, while in Lahore it is 34°-0. In Calcutta there is a considerable reduction 

 of prevalence in the coldest month as compared with that of the maximum prevalence 

 — the percentages of total cholera being 3-13 and 18-68; but this is reduced to 

 insignificance as compared with that exhibited in Lahore, where the respective 

 percentages are 0-07 and 75*22. 



In reference to humidity we find apparent contrasts very sharply defined, more 

 sharply even than those exhibited by the conditions of rainfall. It is questionable 

 how much this difference ought not to be regarded as a mere subordinate concomitant 

 of that in regard to rainfall ; but in so far as atmospheric humidity itself can be 

 supposed to exert any influence on prevalence of the disease, it must be remembered 

 that the contrast lies not so much in absolute conditions of humidity as in relative 

 local conditions. The fact is that the conditions of atmospheric humidity of the two 

 localities come to approximate most closely at different seasons — the approximation 

 occurring when the humidity of Calcutta is at its lowest and that of Lahore at its 

 highest. Putting January and February aside as months in which conditions of 

 temperature exert a disturbing influence on prevalence, we find that the conditions 

 of humidity in Lahore, most closely approaching in degree those present in Calcutta 

 during March and April, are those of August and September. The contrast presented 

 by the two localities, then, in reference to conditions of atmospheric humidity and 

 cholera-prevalence is one in regard to relative local conditions only, the absolute 

 humidity of the localities during their seasons of maximum prevalence is comparatively 

 similar. The same final result may be obtained by addition in one case and by 

 subtraction in another, according as the basis of calculation is greater or less. 



This must be borne in mind in reference to the next point also — the contrast 

 between the conditions of rainfall associated with prevalence of cholera in the two 

 localities. 



In considering the physical conditions of Calcutta we found reason to regard the 

 influence of rainfall as a mediate one, acting through the agency of its direct effects 

 on the soil. In Calcutta, no doubt, the influence of rainfall appears to be mainly 

 exerted through its effects on soil- ventilation, and here there can be no question as 

 to the existence of an apparent contrast between the conditions coincident with 

 maximum prevalence in the two localities. In so far as rainfall acts in obstructing 

 soil-ventilation there is certainly a manifest contrast between the conditions coincident 

 with maximum prevalence in Calcutta and Lahore. The rainfall in the two localities 

 is, however, so very dissimilar, that even were their soils precisely identical in 



could be said regarding it is, that mere range of temperature exerts no appreciable influence on the prevalence 

 of cholera, it has not been deemed necessary to occupy space in giving detailed data leading to no further 

 conclusion. 



