PART I.] Significance of Carbonic Acid in the Soil. 189 



(/) — Wat&r-level . 



The observations on the fluctuation in the water-level are those which have 

 been registered under the superintendence of Dr. Sidney Lynch at the Alipore 

 Jail. The data extend from February 1872 to the present time. The weekly 

 averages in the variations of level for one year's observations, the year specially 

 under review, have been given ; but only the monthly fluctuation for the remaining 

 periods (Table VII, page 203) as the daily figures, or even those of the weekly 

 mean of the observations, would occupy too great space. 



{g) — Statistics of Disease. 



The figures of general mortality and of mortality from cholera which are 

 given in Tables I to VI are those furnished to the Office of the Health Officer 

 of Calcutta. Those regarding fever and dysentery are derived from the Hospital 

 Eegisters of the Presidency and Alipore Jails ; they represent, not the mortality, but 

 the number of cases, and were selected as being presumably more accurate than 

 those furnished by the Police to the Municipality. As the population of the jails 

 averages only about 3,000, it was not considered large enough to furnish information with 

 regard to the general prevalence of cholera with sufficient distinctness. We are under 

 great obligations to both Dr. Sidney Lynch of the Alipore, and Dr. Coull Mackenzie 

 of the Presidency Jails, for the valuable aid which they have given us on very many 

 occasions in connection with our work and for the many data which they have always 

 most readil}' placed at our disposal. 



Having made these introductory explanations with regard to the data which we 

 have brought together, we now proceed to consider the result of the observations as 

 shown in the accompanying tables and diagrammatic charts. 



(2).— The fluctuations in the amount of Carbonic Acid in the Soil. 



It may be premised that the estimation of the amount of carbonic acid in the 

 soil was not undertaken under the idea that this gas itself exerts much influence on 

 the prevalence of disease, but because its amount may be taken as a convenient and 

 fairly accurate index of the degree of the various organic processes taking place 

 between the water-level and the surface. 



(a) — Average amount of Carbonic Acid in the Soil of Calcutta as com'pared with 



that of Munich. — (Chart I.) 



The levels at which the observations were made were not the same in the two 

 localities, those in Calcutta being made at 3 and 6 feet from the surface; those in 

 Munich at 5 and 14 feet. This must be taken into account in the comparison; still 



