appetite thus excited, we obtain the most efficient
protection against the most piercing cold. A starving man is soon frozen
to death; and everyone knows that the animals of prey in the Arctic
regions far exceed in voracity those in 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 the equivalent for a certain amount of food.

The more warmly we are clothed the less food we require. If in hunting
or fishing we were exposed to the same degree of cold as the Samoyedes
we could with ease consume ten pounds of flesh, and perhaps half a dozen
tallow candles into the bargain. The macaroni of the Italian, and the
train oil of the Greenlander and the Russian, are fitted to administer
to their comfort in the climate in which they have been born.

The whole process of respiration appears most clearly developed in the
case of a man exposed to starvation. Currie mentions the case of an
individual who was unable to swallow, and whose body lost 100 lb. in one
month. The more fat an animal contains the longer will it be able to
exist without food, for the fat will be consumed before the oxygen of
the air acts upon the other parts of the body.

There are various causes by which force or motion may be produced. But
in the animal body we recognise as the ultimate cause of all force only
one cause, the chemical action which the elements of the food and the
oxygen of the air mutually exercise on each other. The only known
ultimate cause of vital force, either in animals or in plants, is a
chemical process. If this be prevented, the phenomena of life do not
manifest themselves, or they cease to be recognisable by our senses. If
the chemical action be impeded, the vital phenomena must take new forms.

The heat evolved by the combustion of carbon in the body is sufficient
to account for all the phenomena of animal heat. The 14 oz. of carbon
which in an adult are daily converted into carbonic acid disengage a
quantity of heat which would convert 24 lb. of water, at the temperature
of the body, into vapour. And if we assume that the quantity of water
vaporised through the skin and lungs amounts to 3 lb., then we have
still a large quantity of heat to sustain the temperature of the body.

_II