SH 



THE POPULAR SCIENCE MONTHLY. 



town of Municli, so the numbers concerning cholera obtained from the 

 barracks and prisons of India may be taken as a good sample of the 

 rate of mortality from cholera in the cities themselves. Bryden has 

 given support, in his work on the time and space distribution of chol- 

 era in India, to the reports of barracks and prisons. That cholera 

 should attain its greatest frequency in North Germany during the 

 months of August, September, and October, and that winter should 

 seldom see an epidemic, may be explained by the temperature which 

 prevails in the air and earth. In the class of ectogenous infectious 

 diseases, to which cholera belongs, the temperature, as in all organic 

 processes, has a decided, though it can not be the chief, influence. 

 That cholera is not very dependent on temperature is evidenced by 

 the possibility of the occurrence of an epidemic of cholera during the 

 winter. Why cholera spreads more during the summer and early 

 autumn, as compared with winter and spring, must depend on other 

 causes than temperature. 



It is clear, in my opinion, that the soil and the moisture of the soil 

 play a principal part. The dampness of the soil is, under certain con- 

 ditions, clearly related to the subsoil-water, " Grundwasser." Epi- 

 demics of cholera abound during the time that the "Grundwasser" is 

 falling, when the earth is comparatively dry. By "Grundwasser" is 

 to be understood that condition of dampness of a porous soil when all 

 the pores are filled with water. If water and air together fill up the 

 interstices, then the soil is called simply damp. I have so long and so 

 often spoken on the influence of the rise and fall of the ground-water 

 on the frequency of typhoid fever and cholera, that I imagine a great 

 many scientists credit me with the view that subsoil-water is highly 

 harmful. But such is not the case. The subsoil-water is merely an 

 indication of what is going on, and has no more to do with the actual 

 processes than a dial and the bands have in the going of a clock. The 

 fall of the ground-water by pumping away, or the rise of ground-water 

 by the damming of a stream, has not the least effect on typhoid fever 

 or cholera in the neighborhood. The observation of the level of the 

 surface of the water in springs as an indication of the state of the sub- 

 soil-water is of no value from an etiological point of view, unless the 

 spring be independent of the nearest water-course, and unless at the 

 time of the observation the real state of the spring is a true reflex of 

 the condition of the subsoil-water in its neighborhood. When the 

 information, however, is obtained properly from springs free from 

 objection, then the condition of the ground-water gives the state of 

 moisture and of exchange in the overlying layers much more accurately 

 than an observation made on the atmospheric downfall (rain and dew). 

 Rain may fall for a week without causing any rise in the subsoil-water, 

 and again a rise may occur when there has been no fall of rain for 

 some time. The perusal of Professor Franz Hofmann's work, pub- 

 lished in the " Archives of Hygiene," on the movement of subsoil-water. 



