Excerpt e proper balance between them, how to live long and be useful and happy–this is what the interesting study of physiology and hygiene will teach you. CHAPTER II WHY WE HAVE A STOMACH WHAT KEEPS US ALIVE The Energy in Food and Fuel. The first question that arises in our mind on looking at an engine or machine of any sort is, What makes it go? If we can succeed in getting an answer to the question, What makes the human automobile go? we shall have the key to half its secrets at once. It is fuel, of course; but what kind of fuel? How does the body take it in, how does it burn it, and how does it use the energy or power stored up in it to run the body-engine? Man is a bread-and-butter-motor. The fuel of the automobile is gasoline, and the fuel of the man-motor we call food. The two kinds of fuel do not taste or smell much alike; but they are alike in that they both have what we call energy, or power, stored up