The inert metal composing the steam-engine has no power in itself, nor does power act through the different particles of metal, but it is controlled by the external application of force, which is the result of chemical changes caused by combustion in the fire-box. The metal of the engine has no part in the production of this energy. It does not need to take periods for rest, and if it were possible to supply it continually with water and fuel, it could run steadily from the time it was started until one or more of its essential parts were destroyed through friction.
Necessity for rest
But the engineer and the fireman who drive the engine find it necessary to rest from their labors at certain intervals, not merely for fuel and water, but to prevent serious destruction of body-tissue. This is true because man is compelled by hitherto unrecognized laws to give his body an opportunity, not only for readjustment in its composition, but also for the actual renewal of that power which animates him and makes him an intelligent, self-adjusting, and self-controlled being.
THE OLD PHYSIOLOGY
The stomach as a fire-box
According to the teachings of the old physiology, our stomachs were fire-boxes of the human engine; food was fuel, and the stomach was supposed to transform this fuel into work or energy by a process not entirely clear. Just as it is impossible for the lifeless iron and steel, within itself to transform coal and water into dynamic power, and to apply that power to its own locomotion, so it is impossible and entirely incompatible with reason for mere muscular tissue of the body to extract enough energy from the food we eat to perform the workPhenomenon of rest and sleep necessary for that transformation itself, besides enough more to carry on all the functional activities of the system, and at the same time to do hundreds of foot-tons of physical labor. In this fact lies the key to some understanding of the phenomenon of rest and sleep.
The old physiology was really never able to explain how it was possible for the digestive apparatus to extract, from the amount of food consumed, the enormous amount of energy which the average person expends each day.
REST AND RE-CREATION
Change of occupation not re-creation
These terms are often confused. When one is engaged in some occupation or activity other than his regular vocation, it is commonly called "re-creation." This is a misconception, because it is merely a change in activity and must also be more or less destructive to other sets of nerves or muscular tissue. It is not in reality re-creation—it simply throws the life-power into a new channel, which is more responsive, and calls for less action from those parts of the mechanism which have been employed in the work from which one is seeking relief. It is for this reason that we find some pleasure in a new and different activity, though it, too, may be destructive to the human cell.