A Handbook of Health

by Woods Hutchinson

THE SALIVARY GLANDS

In this diagram are shown the three glands (G) of the left side. The duct (D) from the parotid gland empties through the lining of the cheek; those from the lower glands empty at the front of the mouth under the tongue (T). N, nerve; A, artery; V, vein.

All the juices poured out by these glands, indeed nearly all the fluids or juices in our bodies, are either acid or alkaline. By acid we mean sour, or sharp, like vinegar, lemon juice, vitriol (sulphuric acid), and carbonic acid (which forms the bubbles in and gives the sharp taste to plain soda-water). By alkaline we mean "soap-like" or flat, like soda, lye, lime, and soaps of all sorts. If you pour an acid and an alkali together—like vinegar and soda—they will "fizz" or effervesce, and at the same time neutralize or "kill" each other.

The Use of the Saliva. As the chief purpose of digestion is to prepare the food so that it will dissolve in water, and then be taken up by the cells lining the food-tube, the saliva, like the rest of the body juices, consists chiefly of water. Nothing is more disagreeable than to try to chew some dry food—like a large, crisp soda cracker, for instance—which takes more moisture than the salivary glands are able to pour out on such short notice. You soon begin to feel as if you would choke unless you could get a drink of water. But it is not altogether advisable to take this short cut to relief, because the salivary juice contains what the drink of water does not—a ferment, or digestive substance (ptyalin), which possesses the power 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.