394 VETEEINAEY HYGIENE 



the organism belongs to the soil, but there is evidence to 

 show that soil infection is one of the means by which the 

 disease spreads. 



Soil infection in Epizootic Abortion, Navel-ill, Influenza, 

 and White Scour must not be forgotten, for which see the 

 section dealing with these diseases. 



Fluke disease, especially of sheep, is known to be asso- 

 ciated with certain moist pastures, not because the land is 

 marshy, but for the reason that this class of soil furnishes 

 a suitable nidus for the support of the intermediate host, 

 which is a species of fresh-water snail. Fluke disease and 

 its preventive measures will be considered later, but as it is 

 intimately connected with the draining of the soil, we may 

 conveniently consider this latter question here. 



Draining Soil. — We have stated that it is not possible to 

 exactly define why damp soils are unhealthy excepting on 

 the obvious explanation that they are wet. This takes us 

 no further, unless it can be shown that a damp soil favours 

 the organism of tuberculosis or the poison of rheumatism. 

 Everyday observation tells us how intimately wet and dry 

 soils are associated with health, and for the present we 

 must be content to accept the facts without explaining 

 them. 



Animal life is not the only one affected by wet soils, only 

 the poorer crops are produced when land requires draining, 

 while weeds become abundant, and the ranker and coarser 

 grasses flourish and take the place of good ones. Such land 

 is cold owing to its contained water, and the nitrifying 

 ferments are either destroyed or are only capable of im- 

 perfect work. 



Under these circumstances the land is drained so that 

 the ground water may be lowered by running away. The 

 amount of drainage required depends on the character of 

 the soil, a clay obviously requiring more drainage than a 

 light soil. Drainage also may be shallow or deep ; as a 

 rule, shallow drainage at a depth of about 3 feet from the 

 surface is adopted. To accomplish this trenches are 

 dug according to the slope of the ground, and at a 



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