*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 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