A Handbook of Health. Woods Hutchinson
of turning the starch in our food into sugar. As starch is only very slowly soluble, or "meltable," in water, while sugar is very readily so, the saliva is of great assistance in the process of melting, known as digestion. The changing of the starch to sugar is the reason why bread or cracker, after it has been well chewed, begins to taste sweetish.
This change in the mouth, however, is not of such great importance as we at one time thought, because even with careful mastication, a certain amount of starch will be swallowed unchanged. Nature has provided for this by causing another gland farther down the canal, just beyond the stomach, called the pancreas, to pour into the food tube a juice which is far stronger in sugar-making power than the saliva, and this will readily deal with any starch which may have escaped this change in the mouth. Moreover, this "sugaring" of starch goes on in the stomach for twenty to forty minutes after the food has been swallowed.
Starchy foods, like bread, biscuit, crackers, cake, and pastry, are really the only ones which require such thorough and elaborate chewing as we sometimes hear urged. Other kinds of food, like meat and eggs—which contain no starch and consequently are not acted upon by the saliva—need be chewed only sufficiently long and thoroughly to break them up and reduce them to a coarse pulp, so that they can be readily acted upon by the acid juice of the stomach.
Down the Gullet. When the food has been thoroughly moistened and crushed in the mouth and rolled into a lump, or bolus, at the back of the tongue, it is started down the elevator shaft which we call the gullet, or esophagus. It does not fall of its own weight, like coal down a chute, but each separate swallow is carried down the whole nine inches of the gullet by a wave of muscular action. So powerful and closely applied is this muscular pressure that jugglers can train themselves, with practice, to swallow standing on their heads and even to drink a glass of water in that position; while a horse or a cow always drinks "up-hill." This driving power of the food tube extends throughout its entire length; it is carried out by a series of circular rings of muscles, which are bound together by other threads of muscle running lengthwise, together forming the so-called muscular coat of the tube. By contracting, or squeezing down in rapid succession, one after another, they move the food along through the tube. The failure of these little muscles to act properly is one of the causes of constipation and biliousness. Sometimes the action of the muscles is reversed, and then we get a gush of acid, or bitter, half-digested food up into the mouth, which we call "heart-burn" or "water-brash."
The Stomach—its Shape, Position, and Size. By means of muscular contraction, then, the gullet-elevator carries the food into the stomach. This is a comparatively simple affair, merely a ballooning out, or swelling, of the food tube, like the bulb of a syringe, making a pouch, where the food can be stored between meals, and where it can undergo a certain kind of melting or dissolving. This pouch is about the shape of a pear, with its larger end upward and pointing to the left, and its smaller end tapering down into the intestine, or bowel, on the right, just under the liver. The middle part of the stomach lies almost directly under what we call the "pit of the stomach," though far the larger part of it lies above and to the left of this point, going right up under the ribs until it almost touches the heart, the diaphragm only coming between.[3] This is one of the reasons why, when we have an attack of indigestion, and the stomach is distended with gas, we are quite likely to have palpitation and shortness of breath as well, because the gas-swollen left end of the stomach is pressing upward against the diaphragm and thus upon the heart and the lungs. Most cases of imagined heart trouble are really due to indigestion.
The Lining Surface of the Stomach. Now let us look more carefully at the lining surface of the stomach, for it is very wonderful. Like all other living surfaces, it consists of tiny, living units, or "body bricks" called cells, packed closely side by side like bricks in a pavement. We speak of the mucous membrane, or lining, of our food tube, as if it were one continuous sheet, like a piece of calico or silk; but we must never forget that it is made up of living ranks of millions of tiny cells standing shoulder to shoulder.
These cells are always actively at work picking out the substances they need, and manufacturing out of them the ferments and acids, or alkalies, needed for acting upon the food in their particular part of the tube, whether it be the mouth, the stomach, or the small intestine.
(Greatly magnified)
Showing the mouths of the stomach glands, and the furrows, or folds, of the lining.
The Peptic Juice. The cells of the stomach glands manufacture and pour out a slightly sour, or acid, juice containing a ferment called pepsin. The acid, which is known as hydrochloric acid, and the pepsin together are able to melt down pieces of meat, egg, or curds of milk, and dissolve them into a clear, jelly-like fluid, or thin soup, which can readily be absorbed by the cells lining the intestine.[4]
You can see now why you shouldn't take large doses of soda or other alkalies, just because you feel a little uncomfortable after eating. They will make your stomach less acid and perhaps relieve the discomfort, but they stop or slow down digestion. Neither is it well to swallow large quantities of ice-water, or other very cold drinks, at meal times, or during the process of digestion. As digestion is largely getting the food dissolved in water, the drinking of moderate quantities of water, or other fluids, at meals is not only no hindrance, but rather a help in the process. The danger comes only when the drink is taken so cold as to check digestion, or when it is used to wash down the food in chunks, before it has been properly ground by the teeth.
Digestion in the Stomach. Although usually a single, pear-shaped pouch, the stomach, during digestion, is practically divided into two parts by the shortening, or closing down, of a ring of circular muscle fibres about four inches from the lower end, throwing it into a large, rounded pouch on the left, and a small, cone-shaped one on the right. The gullet, of course, opens into the large left-hand pouch; and here the food is stored as it is swallowed until it has become sufficiently melted and acidified (mixed with acid juice) to be ready to pass on into the smaller pouch. Here more acid juice is poured out into it, and it is churned by the muscles in the walls of the stomach until it is changed to a jelly-like substance.
(Greatly magnified)
The long duct of each gland is but a deep fold of the stomach lining (see note, p. 11). Into this duct the ranks of cells around it pour out the peptic juice.
Digestion in the Small Intestine. The food-pulp now passes on into the small intestine, where it is acted upon by two other digestive juices—the bile, which comes from the liver, and the pancreatic juice, which is secreted by the pancreas.
The liver and the pancreas are a pair of large glands which have budded out, one on each side of the food tube, about six inches below where the food enters the small intestine from the stomach. The liver[5] weighs nearly three pounds, and the pancreas about a quarter of a pound.
Of these two glands, the pancreas, though the smaller, is far more important in digestion. In fact, it is the most powerful digestive gland in the body. Its juice, the pancreatic juice, can do everything that any other digestive juice can, and do it better. It contains a ferment for turning starch into sugar, which is far more powerful than that of the saliva; also another (trypsin), which will dissolve meat-stuffs nearly twice as fast as the pepsin of the stomach can; and still another, not possessed by either mouth or stomach glands, which will melt fat, so that it can be sucked up by the lining cells of the intestine.
What does this great combination of powers in the pancreas mean? It means that we have now reached the real centre and chief seat of digestion, namely, the small intestine, or upper bowel. This is where the food is really