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° 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 condition, known as _exhaustion_, is
not only a matter of temporary inconvenience, but may through repetition
lead to a serious impairment of the health. It should be noted, in this
connection, that the energy of the body is spent in two general ways:
first, in carrying on the vital processes; and second, in the performance
of voluntary activities. Since, in all cases, there is a limit to one’s
energy, it is easily possible to expend so much in the voluntary
activities that the amount left is not sufficient for the vital processes.
This leads to various disturbances and, among other things, renders the
body less able to supply itself with energy.