Physiology and Hygiene for Secondary Schools

by Francis M. Walters

Fig. 84—Simple apparatus for illustrating transformation of energy. Potential energy is converted into heat and heat into motion.

From the Sun to the Cells.—It thus appears that the body comes into possession of energy, and is able to use it, through a series of transferences and transformations that can be traced back to the sun.[72] Coming to the earth as kinetic energy, it is transformed into potential energy and stored in the compounds of plants and in the oxygen of the air. Through the food and the oxygen the potential energy is transferred to the cells of the body. Then by the uniting of the food and the oxygen at the cells (oxidation), the potential becomes kinetic energy and is[pg 192] used by the body in doing its work. The phrase "Child of the Sun" has sometimes been applied to man to express his dependence upon the sun for his supply of energy.

Why Oxygen and Food are Both Necessary.—The necessity for introducing both oxygen and food into the body for the purpose of supplying energy is now apparent. The energy which is used in the body is not the energy of food alone. Nor is it the energy of oxygen alone. It belongs to both. It is due to their attraction for each other and their condition of separation. It cannot, therefore, become kinetic except through their union. To introduce one of these substances into the body without the other, would neither introduce the energy nor set it free. They must both be introduced into the body and there caused to unite.

Bodily Control of Energy.—A fact of importance in the supply of energy to the body is that the rate of transformation (changing of potential to kinetic) is just sufficient for its needs. It is easily seen that too rapid or too slow a rate would prove injurious. The oxidations at the cells are, therefore, under such control that the quantity of kinetic energy supplied to the body as a whole, and to the different organs, is proportional to the work that is done. This is attained, in part at least, through the ability of the body to store up the food materials and hold them in reserve until they are to be oxidized (page 180).

Animal Heat and Motion.—Most of the body's energy is 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 [pg 193]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° 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[pg 194] 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.