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.