As soon as the food enters the stomach, the muscles are excited by the nerves, and the _peristaltic motion_ commences: this is a powerful and constant exercise of the muscles of the stomach, which continues until the process of digestion is complete. During this time the blood is withdrawn from other parts of the system, to supply the demands of the stomach, which is laboring hard with all its muscles. When this motion ceases, and the digested food has gradually passed out, nature requires that the stomach should have a period of repose. And if another meal be eaten immediately after one is digested, the stomach is set to work again before it has had time to rest, and before a sufficient supply of gastric juice is provided. The general rule, then, is, that three hours be given to the stomach for labor, and two for rest; and in obedience to this, five hours, at least, ought to elapse between every two regular meals. In cases where exercise produces a flow of perspiration, more food is needed to supply the loss; and strong laboring men may safely eat as often as they feel the want of food. So, young and healthy children, who gambol and exercise much, and whose bodies grow fast, may have a more frequent supply of food. But, as a general rule, meals should be five hours apart, and eating between meals avoided. There is nothing more unsafe and wearing to the constitution than a habit of eating at any time merely to gratify the palate. When a tempting article is presented, every person should exercise sufficient self-denial to wait till the proper time for eating arrives. Children, as well as grown persons, are often injured by eating between their regular meals, thus weakening the stomach by not affording it any time for rest. As a general rule, the quantity of food actually needed by the body depends on the amount of muscular exercise taken. A laboring man in the open fields probably throws off from his skin and lungs a much larger amount than a person of sedentary pursuits. In consequence of this, he demands a greater amount of food and drink.