expended as heat in
keeping warm. It is estimated that as much as five sixths of the whole
amount is used in this way. The proportion, however, varies with different
persons and is not constant in the same individual during different
seasons of the year. This heat is used in keeping the body at that
temperature which is best suited to carrying on the vital processes. All
parts of the body, through oxidation, furnish heat. Active organs,
however, such as the muscles, the brain, and the glands (especially the
liver), furnish the larger share. The blood in its circulation serves as a
_heat distributer_ for the body and keeps the temperature about the same
in all its parts (page 33).

Next to the production of heat, in the consumption of the body's energy,
is the production of motion. This topic will be considered in the study of
the muscular system (Chapter XV).

*Some Questions of Hygiene.*--The heat-producing capacity of the body
sustains a very important relation to the general health. A sudden chill
may result in a number of derangements and is supposed to be a
predisposing cause of _colds_. One's capacity for producing heat may be so
low that he is unable to respond to a sudden demand for heat, as in going
from a warm room into a cold one. As a consequence, the body is unable to
protect itself against unavoidable exposures.

_Impairment of the heat-producing capacity_ is brought about in many ways.
Several diseases do this directly, or indirectly, to quite an extent. In
health too great care in protecting the body from cold is the most potent
cause of its impairment. Staying in rooms heated above a temperature of
70 deg. F., wearing clothing unnecessarily heavy, and sleeping under an excess
of bed clothes, all diminish the power of the body to produce heat. They
accustom it to producing only a small amount, so that it does not receive
sufficient of what might be called _heat-producing exercise_. Lack of
physical exercise in the open air, as well as too much time spent in
poorly lighted and ventilated rooms, tends also to reduce one's ability to
produce heat. Moreover, since most of the heat of the body comes from the
union of oxygen and food materials at the cells, a lack of either of these
will interfere with the production of heat.

*Results of Exhaustion.*--Through overwork, or excesses in pleasurable
pursuits, one may make greater demands upon the energy of his body than it
can properly supply. The resulting co