SANITARY RELATIONS OF THE SOIL. 333 



change of place. And if it has properties or contains matters in one 

 place which are not remarked in a neighboring place, they can not 

 originate in the air itself, but must be derived from the locality from 

 which they are communicated to it, and are then carried away in the 

 free atmosphere, to disappear by dilution and other processes. 



The same is the case with the local water. All the water that we 

 drink on the earth falls from the sky, and is everywhere of precisely 

 the same composition. Only when it penetrates the soil is it changed 

 by taking up matter which is derived from the ground through which 

 it flows, a fact that was mentioned by Hippocrates. And the local 

 admixtures disappear from water, partly by dilution, partly by chem- 

 ical changes, just as they do from the air ; only in a lesser degree and 

 more slowdy, because water is present in the soil in smaller quantity and 

 moves more sluggishly than air. This purification of the water takes 

 place not only during its continuous retention and movement in porous 

 soils, but also in open river-beds and streams. Brunner and Emmerich 

 have drawn water from the Isar at numerous places between the 

 mountains and the mouth of the river at the Danube, on the same day 

 and have found it essentially alike everywhere, although the stream 

 receives considerable admixtures from the towns on its banks. 



What is there that does not fall into the Elbe in its course from 

 Bohemia down to the sea? Yet filtered Elbe w r ater is considered a 

 pure drinking-water at Hamburg and Altoona. 



The river Trent receives, before it reaches Nottingham, the sewer- 

 water of two million people dwelling on its banks, amounting to at 

 least five hundred thousand gallons a day, yet its waters at that city are 

 clear, sweet-smelling, and chemically free from injurious constituents. 



At Paris, the collecting sewer of CTichy pours a great stream of 

 blackish water into the gently flowing Seine below the bridge of 

 Asnieres, by which the river is so fouled that neither fish nor plants 

 can live in it ; but at Meulan, a few miles below Paris, every trace of 

 impurity has disappeared from the stream. 



When the air and water at any place are contaminated, the con- 

 tamination does not proceed from any combination or decomposition of 

 those two elements, but from qualities of the place, and they soon 

 purify themselves again. An impurity cleaves longest and most tena- 

 ciously to the soil, which suffers no change of place, like air and water. 

 While formerly we esteemed the hygienic value of the air first, of 

 the water second, and of the soil third, we should now reverse the 

 order. 



The influence of the soil upon the health of those living upon it is 

 brought out very plainly during the prevalence of epidemic disease-. 

 That malarial diseases, like intermittent fevers, originate from the soil, 

 is already accepted ; and the more exact studies in recent times of the 

 manner in which cholera, abdominal typhus, yellow fever, and the 

 plague are spread, has convinced many that these diseases, also, which 



