lungs is the temperature of the body quite independent
of the surrounding medium.

The most trustworthy observations prove that in all climates, in the
temperate zones as well as at the equator or the poles, the
temperature of the body in man, and in what are commonly called
warm-blooded animals, is invariably the same; yet how different are
the circumstances under which they live!

The animal body is a heated mass, which bears the same relation to
surrounding objects as any other heated mass. It receives heat when
the surrounding objects are hotter, it loses heat when they are
colder, than itself.

We know that the rapidity of cooling increases with the difference
between the temperature of the heated body and that of the
surrounding medium; that is, the colder the surrounding medium the
shorter the time required for the cooling of the heated body.

How unequal, then, must be the loss of heat in a man at Palermo,
where the external temperature is nearly equal to that of the body,
and in the polar regions, where the external temperature is from 70
deg to 90 deg lower!

Yet, notwithstanding this extremely unequal loss of heat, experience
has shown that the blood of the inhabitant of the arctic circle has
a temperature as high as that of the native of the south, who lives
in so different a medium.

This fact, when its true significance is perceived, proves that the
heat given off to the surrounding medium is restored within the body
with great rapidity. This compensation must consequently take place
more rapidly in winter than in summer, at the pole than at the
equator.

Now, in different climates the quantity of oxygen introduced into
the system by respiration, as has been already shown, varies
according to the temperature of the external air; the quantity of
inspired oxygen increases with the loss of heat by external cooling,
and the quantity of carbon or hydrogen necessary to combine with
this oxygen must be increased in the same ratio.

It is evident that the supply of the heat lost by cooling is
effected by the mutual action of the elements of the food and the
inspired oxygen, which combine together. To make use of a familiar,
but not on that account a less just illustration, the animal body
acts, in this respect, as a furnace, which we supply with fuel. It
signifies nothing what intermediate forms food may assume, what
changes it may undergo in the body; the last change is uniformly the
conversion of its