PART l] No Single Meteorological Condition Determines Cholera-prevalence. 241 



TABLE XLII. 



CoTnparismi of the characters of the months initiating and terminating the 

 various seasons of Gholera-'prevalence. 



Here we find minor cholera-prevalence invariably associated with relative elevation 

 of the water-level, with either decreased or unaltered soil-ventilation, and with 

 increased or unaltered atmospheric humidity. The remaining meteorological conditions 

 accompanying it sometimes show an increase and at others a decrease, but the close 

 connection of rainfall and prevalence is still very distinctly indicated. 



The entire series of data at disposal do not point to any single meteorological 

 condition as the determinant of the phenomena of the seasonal fluctuations in the 

 prevalence of cholera in Calcutta. They indicate depression of the water-level, free 

 ventilation of the soil, and a relatively low degree of atmospheric humidity as the 

 conditions most influential in promoting the prevalence of the disease. When these 

 conditions are simultaneously present, the maximum prevalence occurs, but one or 

 other may be present at other times in very high degree without the prevalence 

 necessarily showing a corresponding elevation. In February, March, April and May, 

 all the favourable conditions are present, and the disease attains its maximum of 

 prevalence ; but in November, December and January, when, although the atmospheric 

 humidity is very low, the water-level is relatively high, and the soil-ventilation obstructed, 

 the prevalence does not nearly equal that of the former period. In June, again, 

 as compared with May, there is a great diminution in prevalence, when our data 

 regarding the carbonic acid in the soil-air do not warrant us in regarding the 

 soil-ventilation as diminished, but at this time the atmospheric humidity is greatlv 

 increased, and the water-level undergoes a considerable elevation. 



