HOW THIS BODY OF OURS FUNCTIONS, TOLD SIMPLY
If we take a human body and eliminate from it, theoretically, such things as the processes of thought and such things as the functions of reproduction of its kind, and growth and replacement of waste, and repair of woundsif, in short, we eliminate the processes the nature of which we know nothing about (which is true of thought), and the building up of new tissuewe find that the body is merely an engine for the production of energy.
The energy arises from the combustion of food products, just as the energy of an automobile arises from the combustion of gasoline.
And, as in any engine, the chemical conversion of one form of energy into another results in the formation of certain by-products. Thus in the automobile, the chemical by-products of the combustion of gasoline come out of the exhaustfor one thing, the deadly carbon monoxide gas. Just what the nature of these chemical processes in the human body are, we will consider when we begin the study of the chemistry of exercise.