carbon into carbonic acid, and of its hydrogen
into water. The unassimilated nitrogen of the food, along with the
unburned or unoxidised carbon, is expelled in the urine or in the
solid excrements. In order to keep up in the furnace a constant
temperature, we must vary the supply of fuel according to the
external temperature, that is, according to the supply of oxygen.

In the animal body the food is the fuel; with a proper supply of
oxygen we obtain the heat given out during its oxidation or
combustion. In winter, when we take exercise in a cold atmosphere,
and when consequently the amount of inspired oxygen increases, the
necessity for food containing carbon and hydrogen increases in the
same ratio; and by gratifying the appetite thus excited, we obtain
the most efficient protection against the most piercing cold. A
starving man is soon frozen to death. The animals of prey in the
arctic regions, as every one knows, far exceed in voracity those of
the torrid zone.

In cold and temperate climates, the air, which incessantly strives
to consume the body, urges man to laborious efforts in order to
furnish the means of resistance to its action, while, in hot
climates, the necessity of labour to provide food is far less
urgent.

Our clothing is merely an equivalent for a certain amount of food.
The more warmly we are clothed the less urgent becomes the appetite
for food, because the loss of heat by cooling, and consequently the
amount of heat to be supplied by the food, is diminished.

If we were to go naked, like certain savage tribes, or if in hunting
or fishing we were exposed to the same degree of cold as the
Samoyedes, we should be able with ease to consume 10 lbs. of flesh,
and perhaps a dozen of tallow candles into the bargain, daily, as
warmly clad travellers have related with astonishment of these
people. We should then also be able to take the same quantity of
brandy or train oil without bad effects, because the carbon and
hydrogen of these substances would only suffice to keep up the
equilibrium between the external temperature and that of our bodies.

According to the preceding expositions, the quantity of food is
regulated by the number of respirations, by the temperature of the
air, and by the amount of heat given off to the surrounding medium.

No isolated fact, apparently opposed to this statement, can affect
the truth of this natural law. Without temporary or permanent injury
to health, the Neapolit