240 



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



TABLE XLI. 



Comparismi of the average monthly characters of the periods of Major aiid Minor 



Cholera-prevalence in Calcutta. 



MKTEOBOLOGICAr, CONDITIONS. 



Atmospheric Pressure ... 



„ Temperature 



„ Humidity 



Eaihfall 



Water-level 



Temperature of the soil 



Relative amount of the carbonic acid in the soil-air 



Period of major 

 prevalence. 



29-847 

 77°-9F. 

 72-5 



3"-23 

 13'-3 

 77=-5 



3 



Period of minor 

 prevalence. 



29-614 



83°-3 F. 



87- 



12"-17 



lO'-O 



81°-8 



4 



Here the combined periods of medium and maximum prevalence, as compared with 

 that of minimum, are shown to be characterised by higher atmospheric pressure, by 

 lower atmospheric and soil-temperature, by lower humidity and rainfall, and by greater 

 ventilation of the soil and depression of the water-level. Taking the entire series of 

 comparisons, it would appear that the conditions most closely connected with the seasonal 

 prevalence of cholera in Calcutta are those of water-level and soil-ventilation. Both 

 water-level and soil-ventilation appear, however, to be mainly determined here by 

 the rainfall, so that the conditions of rainfall and prevalence must also be intimately 

 connected. That they actually are so, is indicated by the coincidence of maximum 

 rainfall with minimum cholera; and that the connection between them is not direct 

 has been already shown by the results of the comparison of the data of rainfall and 

 "prevalence of individual months. If, then, rainfall exert any influence on the prevalence 

 of cholera in Calcutta, it would appear that it must do so through the medium of its 

 direct action on the conditions of the soil. 



When we compare the characters of the months terminating the various seasons 

 of prevalence with those of the months immediately succeeding them and ushering 

 in the following seasons, very similar conclusions are arrived at. 



The following table shows the characters of February compared with January, of 

 May compared with June, of June compared with July, and of October compared with 

 September. The month of minor prevalence is placed after the other throughout the 

 sub-divisions of the table, and the results of the comparisons are separately stated in 

 columns indicating, in regard to the various meteorological conditions, the increase or 

 diminution occurring coincidently with decreased prevalence. 



