llary from the theory of combustion; and we may
consider respiration as an operation in which oxygen gas is
continually passing from the gaseous to the concrete state; it will
therefore give out at every instant the heat which it held in
combination, and this heat, being conveyed by the circulation of the
blood to all parts of the body, is a constant source of heat to the
animal.

These facts likewise enable us to explain the reason, why an animal
preserves the same temperature, notwithstanding the various changes
which occur in the temperature of the surrounding atmosphere. In
winter the air is condensed by the cold, the lungs therefore receive
a greater quantity of oxygen in the same bulk, and the heat
extricated will be proportionally increased. In summer, on the
contrary, the air being rarefied by the heat, a less quantity of
oxygen will be received by the lungs during each inspiration, and
consequently the heat which is extricated must be less.

For the same reason, in northern latitudes, the heat extricated by
respiration will be much greater than in the southern. By this simple
and beautiful contrivance, nature has moderated the extremes of
climate, and enabled the human body to bear vicissitudes which would
otherwise destroy it.

Of all the phenomena of the animal body, there is none at first sight
more remarkable, than that which animals possess of resisting the
extremes of temperature.

The heat of the body, as has already been observed, continues at the
same degree, though the temperature of the atmosphere be sometimes
considerably hotter, at other times considerably colder, than the
animal body: so that man is able to live, and to preserve the
temperature of health, on the burning sands of Africa, and on the
frozen plains of Siberia.

The alterations of temperature which the human body has been known to
bear, without any fatal or even bad effects, are not less than 400
degrees or 500 degrees of Fahrenheit. The natural heat of the human
body is 96 degrees or 97 degrees. In the West Indies, the heat of the
atmosphere is often 98 degrees or 99 degrees, and sometimes rises
even to 126 degrees, or 30 degrees above the temperature of the human
body, notwithstanding which, a thermometer put in the mouth points to
96 degrees or 97 degrees. The inhabitants of the hot regions of
Surinam support, without inconvenience, the heat of their climate. We
are assured that in Senegal, about the latitude of 17 degrees, t