388 VETEEINAEY HYGIENE 



in the superficial layers of the soil, which is obtained from 

 the ground water by means of capillary attraction. One 

 function of sand in a soil is to open up the earth so that 

 this capillarity may occur. 



A great deal has been written on the subject of ground 

 water and disease. It is undoubted that if the ground 

 water is near the surface such sites are not healthy, they are 

 damp, and damp soils have a deleterious effect on the 

 general health of man and animals. But it is difficult to 

 understand how the fluctuations of the ground water can be 

 held responsible for the production of such diseases as 

 enteric or cholera, and the general opinion now appears to 

 be against their having any such influence. 



If, for instance, we take three diseases, cholera, 

 anthrax, and South African ' Horse- Sickness,' all intimately 

 associated with rainfall, it by no means follows that because 

 the ground water fluctuates that this is the cause of the 

 trouble. It would be as reasonable to say that because the 

 rivers are running fuller cholera and anthrax break out. 

 In both cases the rise of the ground water, and the 

 increased volume of water in rivers, merely indicate a 

 recent rainfall. 



Certainly so far as anthrax and African ' Horse- Sickness ' 

 are concerned, we must look for some other condition 

 associated with rainfall, rather than the obvious one of a 

 rise in the level of the ground water. 



It was supposed that as the result of the rise of the 

 ground water, the air which would be thus driven out of 

 the soil contained emanations deleterious to health, while 

 at the same time substances got washed into the wells, the 

 result of the rainfall percolating through the earth, and 

 this was held to be sufficient to account for cholera and 

 enteric, but the evidence is not convincing. 



Air in the Soil. — All soils excepting the densest rocks 

 contain air, as much as 50 per cent, may be found in loose 

 sands. The gases found are oxygen, nitrogen, and carbonic 

 acid, the latter being in much greater portion than that of 

 the atmosphere, in fact two hundred and fifty times 



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