ne--namely, by the union of the oxygen of the air with
the carbon and hydrogen of the fuel. The only real difference between
the two kinds of combustion is, that in respiration the process is
conducted with an extreme degree of slowness, whilst in the ordinary
fire the combinations take place rapidly, and the heat being evolved
in a much shorter time is proportionately the more intense.

3. The temperature of the external parts of the animal body varies with
the nature and quantity of the food supplied to it, and also depends
upon the state of the weather and the character of the protection
afforded to it.

The colder the air, the greater will be the quantity of food required,
and the more complete the shelter. In other words, a diminution of
temperature, no matter how caused, will necessitate an increased amount
of food and more perfect shelter, in order to maintain at the proper
degree of heat the fluids of the body. It is only the external parts of
the body that become cold: so long as the animal is in health its blood
always maintains the same degree of temperature; but in cold weather the
blood is subjected to a greater cooling power than it is in warm
weather, and this cooling power it can only resist by taxing more
extensively the heat-producing resources of the body.

4. Exposure to wet, even in warm weather, will tend to reduce the
temperature of the body, since the conversion of water into vapor can
only be effected at the expense of heat, which heat must be in great
part extracted from the body of the animal itself.

5. No possible increase of food, however nutritious it may be, can
suffice to keep up the due warmth and healthy condition of the animal
frame in winter, if shelter from cold and rain be not simultaneously
effected. On the contrary, an animal well protected from the winter
blasts will require much less food than if it were placed in an exposed
position. The reason of this is, that the amount of food which an animal
exposed to great cold consumes to maintain the temperature of its body
would, under opposite conditions, be stored up in the form of permanent
"increase"--beef or mutton for the butcher, in fact.

The fat-forming constituents of the food of stock are in no case
converted into permanent fat, except when they exceed in quantity the
amount required to keep up the internal heat of the animal; but when
this is constantly reduced by exposure to a wintry temperature, the
food becomes ins