*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° 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.