Personal hygiene and physical training for women

by Anna M. Galbraith

Gastric juice does not dissolve and chemically change all food that enters the stomach, but acts only on that class of foods called proteins, converting them into peptones.

The changes which food undergoes in the stomach are as follows: food is disintegrated; meat is broken up, gelatin dissolved; the muscle-fibers fall apart, and are split into disks and sarcous elements; the framework of fatty tissue undergoes similar dissolution of cellular membranes; milk is curdled; the caseinogen is transformed into casein, and the latter broken down by pepsin. Bread and other starchy foods are disintegrated, some of the starch being formed into sugar by ptyalin. The other vegetable foods are but little digested by this viscus. The whole is broken into irregular fragments by the disintegrating power of the stomach and gradually converted into chyme, the creamy emulsion which passes through the pylorus into the intestines. The passage from the stomach into the duodenum is aided by the motor activity of this organ.

The Mechanics of Digestion in the Stomach.—Recent investigations, especially those of Cannon, have thrown much light on this subject. The food introduced into the stomach from the esophagus is lodged first in the fundus or cardiac end of the stomach; from here it is moved by slow degrees toward the pylorus, from which it enters the small intestine. Formerly it was taught that this movement was brought about by a churning motion of the stomach throughout its entire length. Cannon has shown the error of this conclusion. From his observations it appears that the stomach is quiet at first. The waves of peristaltic constriction begin at the duodenal and middle portions and move the food toward the pylorus. In this way the constrictions that begin near the pyloric end gradually extend to the cardiac end. The latter part of the stomach is distended after a full meal, but gradually diminishes in size during digestion.

Moreover, there is a difference in the character of the gastric juice coming from the different areas of the stomach; that from the middle portion being acid, and that from the cardiac and pyloric being neutral or nearly so. These facts show that the food remains for some time in the fundus and meets there a neutral liquid; consequently, the alkalinity of the mass is retained for a time, and the saliva acts upon the starch for a much longer period than has been supposed.

It is believed that the length of time which food remains in the stomach varies with its kind. The digesting mass is not forced into the intestine until it becomes well saturated with the free acid of the stomach, a result that will be reached later with a meat than with a vegetable diet; for it is plain that much more acid will be required to combine with the proteins of meat than with the smaller amounts in the carbohydrate foods, and so free acid is longer in accumulating.

Digestion is aided by the movements of the food mass through the contractions of the walls of the stomach, so that anything which lowers the tone of the stomach or impairs the integrity of its lining membrane seriously interferes with the digestive processes.

The nature of the food influences the rate of its passage through the pylorus. It has been shown by means of the x-rays that when the meal consisted of lean meat, suet, and rice, properly cooked and prepared in such a manner that the constituents were properly mixed together, the carbohydrates (rice) began to leave the stomach in fifteen minutes, but the protein (lean meat) and fat did not begin to leave it under one-half hour, and were much longer in passing through.

It was further found that in a normal stomach a meal of rice and potatoes gets out of the stomach rapidly, no trace being left in three hours, while a meal of protein and fat meat was much slower, some being present six hours after the meal. Indigestible substances are rejected by the sphincter and returned to the digestive cavity over and over again, but in the course of time the sphincter relaxes and the peristaltic contractions increase, until the force is sufficient to drive through the opening hard substances like peas, plum-stones, and coins.

The Absorption of Food from the Stomach.—A very wide-spread misconception prevails in regard to the amount of absorption that takes place through the gastric walls. This is very limited indeed; some sugar, alcohol and other fluids, and a small proportion of nitrogenous matter are taken up, but that is all. The legitimate rôle of the stomach is a peptonizer and grinder only. Absorption of nutrients is the special work of the intestines, and occupies but a subordinate place in the duties of the stomach.

Proteins undergo peptonization, but that does not change them sufficiently. The mere splitting into peptones, formerly thought sufficient, is now known to be quite inadequate. Recent researches have shown that the complex protein molecule has to be quite crushed into a heterogeneous assemblage of fragments, from which those suitable for building up into the body protein are selected for that purpose, the remainder being used as fuel; that is, as a source of energy. In the case of the other food principles, fats and starches, the chemical processes are much simpler.