CHOLERA. 179 



chain of cases from one year's end to the other by which the 

 infection is handed on. Hueppe, on the other hand, main- 

 tains, as above stated, that the bacillus can have a distinct 

 saprophytic existence, and points to the fact that in places 

 analogous to the delta of the Ganges it has a marked 

 tendency to become endemic. 



As an example of this we may summarize the results of 

 Macleod's observations on cholera in Shanghai. He says that 

 " the remarkable regularity of the time of outbreak, period 

 of duration, and time of cessation of the disease, so far as 

 I am aware, has no parallel on record." The country round 

 Shanghai is strikingly like that of the deltas of the Ganges 

 and the Nile ; "in each there is the alluvial deposit, rich in 

 organic matter, and the high ground- water level, yet in 

 the Ganges delta the disease is prevalent all the year round ; 

 at the mouth of the Yang-Tsze it occurs with the regularity 

 of a crop at the same season yearly ; in the delta of the 

 Nile it occurs only occasionally but at the same season as at 

 the mouth of the Yang-Tsze. The two latter regions have 

 at least weekly communication with India. Some causes or 

 combination of causes are prevalent all the year round at the 

 mouth of the Ganges ; at one season every year, viz, late 

 summer and autumn at the mouth of the Yang-Tsze ; and 

 at the same season, but not every year at the mouth of the 

 Nile." 



There must then in these three regions be perfectly distinct but local 

 conditions which must determine the difference in the behaviour of cholera 

 in these various regions. The general characters of the soil, the ground 

 water, and position are much the same, but there are well-marked differ- 

 ences as regards temperature, population and methods of cultivation. In 

 the delta of the Ganges cholera is absolutely endemic, it is never absent ; the 

 poison, whatever may be its nature, is therefore always present. " From 

 the position and climate, the temperature of the soil varies little throughout 

 the year, and is never so low that some vegetable growth is not active. 

 At the mouth of the Yang-Tsze (where cholera is prevalent only during 

 certain parts of the year), the poison is endemic or is introduced shortly 

 before the time that cholera breaks out each year, in which case it 

 is curious that it should always be at the same time, there being no means 

 of communication with a cholera infected country opened up specially at 

 that time, communication with India being weekly. Here the climate 

 admits of a greater range in the soil temperature than at the mouth of the 

 Ganges, there being great extremes of both heat and cold. The soil heats 

 more slowly than the air, hence perhaps it is the determining cause for the 

 spread of the disease in the late summer and autumn, as already described, 

 and of its absence in winter and spring. " It is evident from this statement 



