Motive force of simple alternate contraction and relaxation in the muscles, which, acting through joints, tendons, and levers, does work of endless variety.
8.

A deficiency of food, drink, or air, first disturbs, then stops the motion and the life.
Carrying out this analogy, you will at once see why a person working hard with either body or mind requires more food than the one who does but little.

The food taken into the human body can never be a simple element.
We do not feed on plain, undiluted oxygen or nitrogen; and, while the composition of the human body includes really sixteen elements in all, oxygen is the only one used in its natural state.

I give first the elements as they exist in a body weighing about one hundred and fifty-four pounds, this being the average weight of a full-grown man; and add a table, compiled from different sources, of the composition of the body as made up from these elements.

Dry as such details may seem, they are the only key to a full understanding of the body, and the laws of the body, so far as the food-supply is concerned; though you will quickly find that the day's food means the day's thought and work, well or ill, and that in your hands is put a power mightier than you know,--the power to build up body, and through body the soul, into a strong and beautiful manhood and womanhood.
ELEMENTS OF THE HUMAN BODY.
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