CHAPTER VII 



SOILS 



We are very deficient in information as to the part played 

 by soils in the production of disease ; at one time the con- 

 nection between the two was considered undoubted, but little 

 by little as our knowledge has become more exact, the 

 influence of soil has appeared subordinate to other con- 

 ditions, which though associated with definite geological 

 formations, are yet known to be more important than the 

 soil itself. 



For instance, malaria is a term employed by everyone to 

 indicate the existence of a definite form of fever, which was 

 supposed to depend upon certain emanations from the soil. 

 The class of soil where malaria was present, or might be 

 expected to be met with was perfectly well known, and the 

 cause of the disease was pictured as an organic vapour 

 arising out of the earth at certain times of the day. 



An immense amount of information was collected from 

 all parts of the world bearing on this question, and 

 gradually it became perfectly well known that low-lying or 

 marshy districts, particularly in the tropics, were malarial, 

 and that altitude gave relative protection. 



Wet soils filled with the decomposing vegetable matter of 

 centuries were known to be most malarial ; even disturbing 

 the earth, as in engineering operations, induced malaria by 

 allowing of the escape of the vapours which had hitherto 

 been sealed up, and in other ways the conclusion was 

 irresistibly arrived at that soil of a particular kind and 

 malaria were most intimately connected. 

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