CHOLERA. 177 



tinuous currents are created, organic matter of all kinds is 

 washed away, air is driven out from the subsoil owing to the 

 rising of the ground water, and all the conditions become 

 unfavourable for the growth of the organism. The fact that 

 vegetation has been mentioned, as associated with climate in 

 the production of cholera, requires some explanation, which 

 will be given later. Dr. Macleod, writing on the subject of 

 climate itself, says : 



" 



Cholera makes its appearance in Shanghai every summer with start- 

 ling regularity, Before the end of July it is hardly met with, by the end of 

 August it is well marked, in September it is in lull swing, not quite so 

 virulent in October, and in the beginning of November an occasional case 

 may be heard of, after which time it disappears entirely till the following 

 late summer. For twenty years this has gone on with unfailing regularity 

 under the observation of medical men now resident, and for how long 

 previously no one can estimate." He then goes on to describe the weather 

 in June as damp and hot, in September as hot, damp, and muggy, in 

 October as cool and wet during the first part, and as frosty towards the end, 

 " at Christmas there is usually ice, there may be snow." He then says, " so 

 far as temperature of the air is concerned, we enjoy tropical heat for nearly 

 a couple of months before the disease breaks out ; it is most virulent in the 

 hot, damp September, and does not disappear until after the hoar-frosty 

 mornings are experienced " (the end of October). 



Dealing with the same subject Koch has stated that in 

 no part of the world, of which the climate, the geology, and 

 the epidemiology are known, does cholera occur all the year 

 round except in the province of Bengal, and he says : 



" All authors are agreed, that the delta of the Ganges is the true home 

 of cholera, and I have come to the conclusion that this is the case, and that 

 there are no other places of origin of cholera in India. For the only district 

 in India, where cholera prevails continually year after year in a uniform 

 manner, is the delta of the Ganges. In all other places it shows marked 

 variations, or it may even disappear altogether for a shorter or a longer time. 

 In certain places, for example in Bombay, it never entirely disappears, but 

 it is highly probable, that on account of the unusually active trade with the 

 rest of India it is constantly being imported there afresh." He then 

 describes this tract as a perfectly flat country only slightly raised above the 

 sea level, which, during rainy seasons, is almost entirely under water in the 

 lower part of the delta, where the "Ganges and the Brahmapootra break up 

 into a network of water courses, in which the sea water, mixing itself with 

 the river water, flows hither and thither with the tide, and at flood time 

 places large tracts of the Sunderbunds under water. A luxuriant vegetation 

 and an abundant animal life have developed in this uninhabited region, 

 which is inaccessible to man not only on account of the floods and the 

 numerous tigers, but is avoided principally on account of the pernicious 

 fever which attacks everybody who remains there even for quite a short 

 time. One can easily imagine how dense the vegetable and animal matter 



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