PART I.] Limits and Character of Soil of Endemic Area of Cholera. 243 



II.— CHOLERA IN THE ENDEMIC AREA GENERALLY, 



CHAPTER I. 



THE RELATION OF VARIOUS PHYSICAL PHENOMENA TO CHOLERA IN OTHER DISTRICTS OF THE 

 ENDEMIC AREA IN THE BENGAL PRESIDENCY. 



(a) Geographical limits and character of the soil of the Endemic area. 



Having discussed the question of the relation of cholera to certain generally 

 studied physical phenomena in Calcutta as fully as the statistical and other data 

 seemed to warrant, we now propose applying the same process to such other 

 parts of India as present a cholera-history more or less closely identical with that 

 of Calcutta. It will not be necessary to treat the several stations which belong to 

 this class with the same minuteness as Calcutta ; nor indeed, were it desirable to do 

 so, is there sufficiently precise information in existence regarding them to render 

 such a description possible. 



In his important work, " Cholera Epidemics of Recent Years," Dr. Bryden 

 defines the region of endemic cholera in the Presidency of Bengal as "the basin 

 having the hill-country east of the Brahmaputra for its eastern margin, and the 

 Rajmahal and Cuttack hills for its western margin. Its northern limit is the 

 terai of the Himalayas from Lower Assam on the east to the terai of the Purneah 

 district on the west, and its southern limit is the sea border of the Bay of Bengal, 

 from Pooree in the west, to beyond the mouth of the Brahmaputra in the east " 

 (page 61). 



In may be observed at starting that the history of cholera all over India 

 presents one common feature, and that is that it can only be fairly regarded as 

 endemic in such localities as manifest a close resemblance in the more superficial 

 layers of their geological formation. This feature, it will be found, is more 

 conspicuous than any of the other physical characters to which we shall have occasion 

 to refer. 



We have already indicated generally what characters the surface-soil of Calcutta 

 presents. Mr. Henry F. Blanford in his Physical Geogra'phy describes it in a few 

 words as a mixture of firm sand and clay with decayed animal and vegetable 

 matter — loam, very much like the silt that settles from muddy river-water. Below 

 this, at a distance of from 6 to 10 feet, comes a bed of stiff clay, and below 

 this again a layer of peat resting on alternating layers of sand and clay. 



Mr. Blanford tells us that many years ago a well was sunk in Calcutta to a 

 depth of 481 feet through successive layers of sand, clay, peat and pebbles ; that 



