r the air will alternately
enter and be expelled from the lungs by this alternate dilatation and
contraction of the thorax.

Respiration is a function of such consequence, that death follows if
it is suspended for a few minutes only. By means of this function the
blood is elaborated, and rendered fit to nourish the body; by means
of it the system is, most probably, supplied with irritability; by
means of it the nervous energy is, most likely, conveyed into the
body, to be expended in sensation, and muscular motion. It appears,
likewise, that in this way, animals are supplied with that heat which
preserves their temperatures nearly the same, whatever may be the
temperatures of surrounding bodies.

If any number of inanimate bodies, possessed of different degrees of
heat, be placed near each other, the heat will begin to pass from the
hotter bodies to the colder, till there be an equilibrium of
temperature. But this is by no means the case with respect to
animated matter; for whatever be the degree of heat peculiar to
individual animals, they preserve it, nearly unchanged, in every
temperature, provided the temperature be not altogether incompatible
with life or health. Thus, we find, from experiments that have been
made, that the human body is not only capable of supporting, in
certain circumstances, without any material change in its
temperature, a degree of heat considerably above that at which water
boils; but it likewise maintains its usual temperature, whilst the
surrounding medium is several degrees below frost.

It is evident, therefore, that animals neither receive their heat
from the bodies which surround them, nor suffer, from the influence
of external circumstances, any material alterations in that heat
which is peculiar to their nature. These general facts are confirmed
and elucidated by many accurate and well authenticated observations,
which show, that the degree of heat in the same genus and species of
the more perfect animals, continues uniformly the same, whether they
be surrounded by mountains of snow, in the neighbourhood of the pole,
or exposed to a vertical sun, in the sultry regions of the torrid
zone.

This stability and uniformity of animal heat, under such a disparity
of external circumstances, and so vast a latitude in the temperature
of the ambient air, prove, beyond doubt, that the living body is
furnished with a peculiar mechanism, or power of generating,
supporting, and regulating its