742 Water in Relation to Health and Disease. 
Yorkshire are turned blue and various other hues by the effluent 
refuse of cloth works ; those of Cornwall are reddened by the 
copperas washings of the tin-plate manufactories, or turned 
white by impregnation with china clay ; while in the coal-bearing 
districts they are blackened by the effluent from coal washing. 
Outward and visible signs, however, are not always available 
to make known the presence of poisonous and deleterious sub- 
stances which enter our waterways, and in such cases it is 
only by actual experience of their effects on living things that 
their presence becomes known to the farmer. The absence of 
fish where once they were abundant, the disappearance of aquatic 
plants from the river and its bank, are significant facts in river 
sanitation, if not absolute proof of dangerous pollution. Deadly 
such water may not always be to the live stock of the farm, but 
it is all the same deleterious to health. Under its use young 
stock fail to grow and to thrive, milk production is lessened, 
butter is diminished in quantity and impaired in quality, preg- 
nant animals abort, and active disease and death not unfrequently 
result. 
Notwithstanding all that has been done in recent years with 
the object of preventing the pollution of rivers and their tribu- 
taries, losses and depreciation of live stock from this cause still 
continue to arise, and too frequently to engage the attention of 
our law courts in the settlement of contentious claims. 
As to sewage, its rapid and complete removal from our 
densely populated centres is an indispensable requirement of 
Public Health, and since for many and various reasons its appli- 
cation to the land for agricultural purposes is, under present 
circumstances, impracticable as a general system, our rivers and 
streams are the only receptacles into which it can be discharged 
with reasonable security. The great dilution which it under- 
goes in the former, the rapidity with which it is carried away, 
and the natural purifying influences to which it is exposed are 
sanitary requirements of the first order economically provided by 
our great trunk drains. It cannot be said that the pollution of 
rivers with common sewage is productive of any considerable 
amount of sickness or mortality in our live stock, and perhaps 
for the reasons we have given in regard to dilution and natural 
purification which it undergoes. The same cannot, however, be 
said of it in small tributaries and drains where it is permitted 
to stagnate, and to impregnate the water with products of 
putrescence. 
The mines which have proved most injurious to live stock 
are those of lead, tin, copper, and arsenic. The polluting 
matter from these sources mostly exists in the form of small 
