The Intestines.—The small intestines are continuous with the stomach, and, though very different in shape, are like it in general structure. The bile, which is secreted by the liver, unites with the pancreatic juice, and enters the intestines through a duct about three inches below the stomach. By the joint action of these two fluids, the fatty elements of the food are prepared for absorption. From the mucous membrane, or inner lining of the small intestines, still another juice or fluid flows, whose office is to supplement the work, first, of the saliva in converting starch into sugar; next, of the gastric juice in digesting the albuminoids; and, lastly, of the pancreatic juice and bile in emulsifying the fats. The work of digestion is completed in the small intestines. The indigestible parts of the food are passed into the large intestines, and expelled from the body.
Absorption.—The liquefied food, in its passage through the stomach and small intestines, has been prepared by the various juices for its absorption by the blood vessels and the lacteals, whose minute mouths throng this part of the alimentary canal. The food elements thus absorbed are conveyed to the right auricle, or first chamber of the heart.
Conditions Affecting Digestion.—The quality, quantity, and temperature of the food, and the condition of mind and body, all have an influence upon digestion. In the selection of food, only such articles should be allowed as are fresh, pure, and wholesome. Bread should not be eaten warm. It is more easily digested after being baked a day or two. Flesh of animals recently slaughtered should be thoroughly cooled, and never cooked while yet warm and quivering with life.
Cooking renders many articles of food not only more wholesome and palatable, but also more digestible by reason of the increased temperature. The natural heat of the stomach is about ninety-nine and one-half degrees, at which temperature the operations of digestion are best promoted. Hot soups are therefore a good introduction to the meal. A small glass of ice-water will retard digestion for half an hour.
Sudden joy, anger, grief, or other strong emotion or excitement checks digestion. If the tongue is parched and the mouth dry, the flow of saliva is restrained and the first step in the process of digestion is hindered. The coating of the tongue reflects the condition of the stomach, hence the frequent request of the physician to see the tongue of the patient.
Bodily fatigue destroys appetite and hinders digestion. The expression “I am too tired to eat” is not uncommon.
Intervals for Meals.—Frequent eating is as bad as rapid eating or over-eating. The organs of digestion require periods of rest, in order to renew their strength and restore the juices essential to their perfect operation. No person, except infants and the sick, should require food oftener than once in four hours. If the stomach is in good working order, it will usually complete its task in two hours, unless the food is too great in quantity or too indigestible.
No one should take more than three meals a day, and, to insure sound refreshing sleep and allow the stomach to recover its tone, the last meal should be the lightest and easiest to digest. Dyspeptics and others affected with stomach troubles will find benefit in restricting themselves to two moderate meals a day. Numerous cases are cited of notable cures effected by adopting a regimen of only one meal each day.
Regularity.—Whatever the interval between meals, be it four, five, or six hours, there should be regularity. The stomach, like the mind, forms habits, and the habit of regularity in eating will beget the habit of regularity in digesting and recuperating. The practice of parents in giving children cakes, fruits, and sweetmeats between meals is reprehensible. As a result of habit, many persons grow to feel that a dinner is not complete without a substantial dessert. The mistake consists, not always in the dessert, for that may be as wholesome and nourishing as any part of the meal, but in first fully satisfying the demands of hunger, and afterwards imposing upon the stomach the extra burden of digesting the dessert.