734 Water in Relation to Health and Disease. 
Besides these special functions water also serves other pur- 
poses of a more general character in the animal economy ; for 
instance, it imparts to the tissues a state of mobility, and of 
physical fitness for the exercise of their respective functions. 
It maintains in solution many salts and other matters essential 
to the vital processes of the economy, and it favours those nutri- 
tive exchanges upon which, as we have seen, the growth and 
reparation of the body depend. 
Inasmuch as the body is constantly giving out water by the 
skin as sensible or insensible perspiration, through the lungs 
as vapour, and by the kidneys as urine, the stock of fluid upon 
which life so much depends would soon run out were no pro- 
vision made for its renewal. This, however, is obviated by that 
peculiar sensation termed “ thirst,” which always arises when 
the fluids of the body fall below a certain point. Thirst, there- 
fore, is not, what it might seem to be, a mere local dryness of the 
mouth and throat, but an expression of general deficiency of 
water in the blood and tissues of the entire organism. This is 
shown by the fact that it may be readily allayed by injecting 
water into the veins and without administering it by way of the 
mouth. If more water enters the blood than is necessary for 
the requirements of the system, the surplus is quickly thrown 
off by the kidneys, and with it, as we have seen, more or less 
refuse matter, to which reference has already been made. 
The quantity of water requisite to maintain the body in 
health will vary in different animals, and in the same animal 
under different conditions. The circumstances specially influ- 
encing the amount required are food, temperature, and exertion. 
Animals subsisting on juicy roots and grass require but little to 
drink, while others partaking of dry food, such as hay, corn, 
cake, chaff, &c., need a liberal and regular supply. In hot 
weather and with animals occupying hot stables, when the skin is 
active and freely exhales moisture, the demand will be greater 
than in cold, and more will be required during work than at 
rest. Speaking genei'ally, it may be said that horses doing 
ordinary work consume from seven to nine gallons per day, 
while six to eight gallons suffice to meet the requirements of 
oxen. Milch cows when housed may require a larger amount, 
especially deep milkers. Sheep and pigs will take from three 
quarts to a gallon per day. When suckling, a greater supply is 
needed by all of them. 
In dealing with water in its relations to health, it has to be 
borne in mind that the standard of excellence is not, as might 
be considered, its purity, but its wholesomeness, i.e., the absence 
from it of matters prejudicial to health, and the presence in it 
