materials in the tissues, produce an amount of heat which is efficient to
maintain the temperature of the living body at about 98-1/2 degrees F. This
process of oxidation provides not only for the heat of the body, but also
for the energy required to carry on the muscular work of the animal
organism.

225. Regulation of the Bodily Temperature. While bodily heat is being
continually produced, it is also as continually being lost by the lungs,
by the skin, and to some extent, by certain excretions. The blood, in its
swiftly flowing current, carries warmth from the tissues where heat is
being rapidly generated, to the tissues or organs in which it is being
lost by radiation, conduction, or evaporation. Were there no arrangement
by which heat could be distributed and regulated, the temperature of the
body would be very unequal in different parts, and would vary at different
times.

The normal temperature is maintained with slight variations throughout
life. Indeed a change of more than a degree above or below the average,
indicates some failure in the organism, or some unusual influence. It is
evident, then, that the mechanisms which regulate the temperature of the
body must be exceedingly sensitive.

The two chief means of regulating the temperature of the body are the
lungs and the skin. As a means of lowering the temperature, the
lungs and air passages are very inferior to the skin; although, by giving
heat to the air we breathe, they stand next to the skin in importance. As
a regulating power they are altogether subordinate to the skin.

Experiment 113. _To show the natural temperature of the body_.
Borrow a physician's clinical thermometer, and take your own
temperature, and that of several friends, by placing the instrument
under the tongue, closing the mouth, and holding it there for five
minutes. It should be thoroughly cleansed after each use.

226. The Skin as a Heat-regulator. The great regulator of the bodily
temperature is, undoubtedly, the skin, which performs this function
by means of a self-regulating apparatus with a more or less double action.
First, the skin regulates the loss of heat by means of the vaso-motor
mechanism. The more blood passes through the skin, the greater will be
the loss of heat by conduction, radiation, and evaporation. Hence, any
action of the vaso-motor mechanism which causes dilatation of the
cutaneous capillaries, leads to a larger flow of blood through the skin,
and