Fig. 74—Section of large intestine, showing the coats. 1. Serous coat. 2. Circular layer of muscle. 3. Submucous coat. 4. Mucous membrane. 5. Muscular bands extending lengthwise over the intestine.
Work of the Large Intestine.—The large intestine serves as a receptacle for the materials from the small intestine. The digestive fluids from the small intestine continue their action here, and the dissolved materials also continue to be absorbed. In these respects the work of the large intestine is similar to that of the small intestine. It does, however, a work peculiar to itself in that it collects and retains undigested food particles, together with other wastes, and ejects them periodically from the canal.
Work of the Alimentary Muscles.—The mechanical part of digestion is performed by the muscles that encircle the food canal. Their uses, which have already been mentioned in connection with the different organs of[pg 160] digestion, may be here summarized: They supply the necessary force for masticating the food. They propel the food through the canal. They mix the food with the different juices. At certain places they partly or completely close the passage until a digestive process is completed. They may even cause a reverse movement of the food, as in vomiting. All of the alimentary muscles, except those around the mouth, are involuntary. Their work is of the greatest importance.
Other Purposes of the Digestive Organs.—The digestive organs serve other important purposes besides that of dissolving the foods. They provide favorable conditions for passing the dissolved material into the blood. They dispose of such portions of the foods as fail, in the digestive processes, to be reduced to a liquid state. A considerable amount of waste material is also separated from the blood by the glands of digestion (especially the liver), and this is passed from the body with the undigested portions of food. Then the food canal (stomach in particular) is a means of holding, or storing, food which is awaiting the processes of digestion. Considering the number of these purposes, the digestive organs are remarkably simple, both in structure and in method of operation.
HYGIENE OF DIGESTION
Many of the ills to which flesh is heir are due to improper methods of taking food and are cured by observing the simple rules of eating. Habit plays a large part in the process and children should, for this reason, be taught early to eat properly. Since the majority of the digestive processes are involuntary and the food, after being swallowed, is practically beyond control, careful attention must be given to the proper mastication of the food and to such other phases of digestion as are under control.
Necessity for Thorough Mastication.—Mastication prepares the food for the digestive processes which follow. Unless the food has been properly masticated, the digestive[pg 161] fluids in the stomach and intestines cannot act upon it to the best advantage. When the food is carefully chewed, a larger per cent of it is actually digested—a point of importance where economy in the use of food needs to be practiced.
A fact not to be overlooked is that one cannot eat hurriedly and practice thorough mastication. The food must not be swallowed in lumps, but reduced to a finely divided and pulpy mass. This requires time. The one who hurries through the meal is necessarily compelled to bolt his food. Thirty minutes is not too long to give to a meal, and a longer period is even better.
Perhaps the most important result of giving plenty of time to the taking of food is that of stimulating the digestive glands to a proper degree of activity. That both the salivary and gastric glands are excited by the sight, smell, and thought of food and, through taste, by the presence of food in the mouth, has been fully demonstrated. Food that is thoroughly masticated and relished will receive more saliva and gastric juice, and probably more of other juices, than if hastily chewed and swallowed. This has a most important bearing upon the efficiency of the digestive processes.