=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.