A handbook of invalid cooking

by Mary A. Boland

Mucus of Large Intestine. The mucus secreted by the large intestine is for lubricating only.

Digestion in Different Parts of the Alimentary Tract. Different substances in food are digested in different portions of the alimentary canal, and by different means. Let us begin in the mouth. Taking the classes of foods, starch, one of the carbohydrates, is the one most affected by the ptyalin, or animal diastase, of the saliva. So energetic is the action of ptyalin on starch that 1 part is sufficient to change 1000 parts. Starch is not acted upon by the gastric juice of the stomach at all; however, the continued action of the saliva is not probably interrupted in the stomach. The digestion of starch is completed by the action of the pancreatic and intestinal juices, and consists in its being changed into soluble glucose, which is absorbed in solution.

Sugar. Cane-sugar, or common sugar (also called sucrose), passes through the mouth, unchanged, to the stomach, where it is converted into glucose by the slow action of the acid (hydrochloric) of the gastric juice. Dilute hydrochloric acid has the same action on sugar outside of the stomach.

The action of pancreatic juice on sugar is very marked; it immediately changes cane-sugar into glucose. The effect of intestinal fluid is not well understood, but there is the general agreement that it does not change cane-sugar, neither is cane-sugar, as such, absorbed in the intestine. Bile does not affect it, therefore cane-sugar is digested or converted into glucose either by the stomach or pancreas, or both. It will now be seen that ultimately the same substance, glucose, is obtained from both starch and sugar.

Protein. We now come to the consideration of the digestion of the protein compounds, of which albumen may be taken as a type. Possibly no action except breaking up and moistening takes place in the mouth.[21] Its digestion begins in the stomach, where its structure is broken up and a separation and dissolution of the little sacs which hold it take place. The same thing is partially accomplished outside of the stomach when white of egg is slightly beaten and strained through a cloth. Gastric juice further acts on the albumen itself, forming it into what is called albumen peptone. The digestion of raw and carefully cooked albumen has been found to be carried on very rapidly in the stomach, and the change is essentially the same in both cases, but in favor of the slightly coagulated. When the albumen is rendered hard, fine, and close in consistency by over-cooking, then it is less easy of digestion than when raw.

Absorption. It is probable that the greater portion of the process of digestion and absorption of albumen takes place in the stomach.

Fibrin. Fibrin is also digested in the stomach, and made into fibrin peptone.

Casein. Liquid casein is immediately coagulated by gastric juice, both by the action of free acid and organic matter.

Gelatin. Gelatin is quickly dissolved by gastric juice, and afterward no longer has the property of forming jelly on cooling. Gelatin is more rapidly disposed of than the tissue from which it is produced.

Vegetable Protein. The digestion of the vegetable protein compounds, such as the gluten of wheat and the protein of the various grains, such as corn, oatmeal, etc., is undoubtedly carried on in the stomach, but they must be well softened and prepared by the action of heat and water, or they will not be digested anywhere; and often corn, beans, and grains of oatmeal are rejected entirely unchanged. Partially or imperfectly digested proteins are affected by intestinal juice. It is probable that the function of this fluid is to complete digestive changes in food which have already begun in the stomach.