There are two types of creature in the world--the cold-blooded and the
warm blooded. Frogs, snakes, etc., are examples of the former; cats and
dogs of the latter category. Lizards, snails and fish are cold blooded;
lions, tigers, horses are warm blooded. Man is also a warm blooded
animal.
There is this remarkable distinction between them: That, whereas
cold blooded creatures take on the temperature of their environment
(whatever that may be), warm blooded animals always remain at
approximately the same temperature, no matter what the external heat
or cold may be. Thus, if a frog is placed in a temperature of forty
degrees Fahrenheit, he will soon be of that temperature also. Cold
blooded creatures may even be frozen stiff, and yet revive, when thawed
out. Above a certain temperature of heat, however, they all die.
In the case of warm blooded animals, however, the case is quite
different. Thus, man’s temperature, in health, always remains the
same--about ninety-eight degrees Fahrenheit. No matter whether he is
sweltering in the tropics, or exploring the icy regions of the Polar
Seas, his bodily temperature remains the same. (As soon as he dies,
however, his corpse assumes the temperature of the surrounding air.)
The constant temperature of the human body, therefore, is somehow
dependent upon life. Nature has provided a number of mechanisms and
adjustments to keep the temperature normal. In very cold weather, the
skin contracts, to prevent too large a volume of blood from reaching
the surface, and becoming cooled. In hot weather, the pores of the
skin open, perspiration pours forth, evaporation takes place, and this
serves to cool the body.
The heat of the body is maintained by combustion, burning up the food
we eat; and if too much is yielded, the body disposes of it. But just
why Nature has decided upon the exact degree of bodily heat we possess
is as yet an unsolved mystery. It seems, however, the one best suited
for our purposes.