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



Before any conclusion can be arrived at, however, on this point, data derived from 

 direct observation regarding the actual influence exerted on the soil-ventilation must 

 be acquired, and in the meantime it is well to bear in mind that we have no 

 evidence to show what the effect of the addition of moisture to the soil without coincident 

 obstruction to soil-ventilation might be. We do know how much cholera arises under 

 existing circumstances ; we can form no conception as to what the amount might be 

 under the hypothetical ones. 



CHAPTER II. 



THE PHENOMENA OF SEASONAL FLUCTUATION IN THE PREVALENCE OF CHOLERA CONSIDERED 

 IN REFERENCE TO THE PRINCIPAL THEORIES REGARDING THE ESSENTIAL CAUSE OF THE 

 DISEASE. 



(a) As observed in Calcutta. 



In the earlier part of this report an attempt has been made to ascertain the 

 character of the local physical conditions coinciding with the various degrees of 

 cholera-prevalence in Calcutta at different times during the course of the year. 

 The information thus obtained has next to be considered in reference to various 

 current theories relative to the essential causation of the disease. 



The most important theories are the following : 



\st. — That which regards cholera as essentially caused by direct contagion, — by 

 the direct transfer of a poison, manufactured within the human organism, from one 

 person to another. According to it, any fluctuations in the prevalence of cholera 

 must be dependent on corresponding fluctuations, either in opportunity of transfer, 

 or in the susceptibility of human beings to the influence of the poison. 



^nd. — The so-called " water theory." In this, also, the human organism is 

 regarded as the factory in which a specific poison is produced. By one set of the 

 supporters of the theory, water is regarded merely as one means — -although by far 

 the most important and influential means — by which the poison is diffused, — is 

 transferred from one person to another. By other authorities, however, water is 

 not regarded as a mere vehicle, but as the medium in which the material produced 

 within the human organism attains its maximum of virulence. According to this 

 theory, fluctuations in the prevalence of cholera must essentially depend on 

 corresponding fluctuations in conditions determining, or facilitating, the transfer 

 of materials produced within the human organism to the water, and specially to the 

 drinking water. 



2>rd. — The theory which, while regarding the drinking water of a locality as 

 essentially determining the prevalence of cholera in it, does not regard its influence 

 as necessarily dependent on the introduction of any specific material manufactured 



