This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
Energy, as we have seen, cannot be created from nothing; since the body constantly expends energy, it must have a steady supply. This supply comes from the energy liberated when parts of the body are burned, or, as the chemists say, oxidized, just as that used by a locomotive comes from the burning or oxidation of coal or wood in its furnace. In consequence of this constant oxidation, which destroys the tissues of the body as coal is destroyed in a furnace, new materials must constantly be supplied to make up for those used for oxidation. These new materials are provided in our food. One chief reason of our needing to eat, is that we may replace the parts of the body which have been burned in order to set free the energy which we spend in our muscular movements.
Give an example of the transformation of heat into electrical force. Of electrical force into light. Given a supply of one kind of energy what can we do with it? What would we find if we collected all the final manifestations of energy and turned them back into the original form ?
Why must the body have a steady supply of energy ? Where does the supply come from ?
As a working steam-engine is warm so are our bodies, because all the energy which is set free when substances are burned in them, is not turned into mechanical work, but some of it appears as heat. This keeping warm is a very important matter, for experiment shows that no tissue of the human body works well when cooled down even a few degrees below 98.5° F., which is its natural healthy temperature. Careful experiments prove that when a muscle does work it becomes hotter, and we all know that exercise makes us warm. This shows that the oxidation or burning which takes place in a working muscle does not all become turned into mechanical work, but a good share of it appears as heat. What is true of muscle is true of all other organs of the body: when they work, no matter what their kind of work, their substance is oxidized, and some of the energy set free by the oxidation appears as heat, assisting to keep the body warm, and at its best working temperature.
What is the chemical term for burning? What does food supply?
Point out a chief reason for our need of eating?
Why are our bodies warm ? Why is it important that they should be warm ? How is the temperature of a muscle affected when it works ? Po Other organs resemble muscles in, this respect?
Since the body only works well at a temperature which is higher than that of the air around it (except on a very hot day), and in health always keeps at this temperature, it must lose heat nearly all the time. At night each of us is, in health, just as warm as in the morning; and in the morning as when we went to bed; though we have lost heat to the air during the day, and to the bedclothes at night. In order to keep our bodies at the temperature most suitable to their activity, they must, therefore, generate heat all the time, to compensate for the giving of it from them to the outer world. In this necessity of generating heat we find a second reason for the need of food: we require daily to take into ourselves things which can be burned (or oxidized) in the body, and which in so doing will give off heat.