A Handbook of Health | Page 6

ball, or bolus, and shooting it back down the throat, through
the gullet, into the stomach.
The Intestines. When the food has been sufficiently melted and
partially digested in the stomach, it is pushed on into a long tube called
the intestine, or bowel. During its passage through this part of the food
tube, it is taken up into the veins, and carried to the heart. From here it
is pumped all over the body to feed and nourish the millions of little
cells of which the body is built. This bowel tube, or intestine, which, on
account of its length, is arranged in coils, finally delivers the
undigested remains of the food into a somewhat larger tube called the
large intestine, in the lower and back part of the body, where its
remaining moisture is sucked out of it, and its solid waste material
passed out of the body through the rectum in the form of the feces.
THE JOURNEY DOWN THE FOOD TUBE
The Flow of Saliva and "Appetite Juice." We are now ready to start
some food-fuel, say a piece of bread, on its journey down our food tube,
or alimentary canal. One would naturally suppose that the process of
digestion would not begin until the food got well between our teeth; but,
as a matter of fact, it begins before it enters our lips, or even before it
leaves the table. If bread be toasted or freshly baked, the mere smell of

it will start our mouths to watering; nay, even the mere sight of food, as
in a pastry cook's window, with the glass between us and it, will start
up this preparation for the feast.
This flow of saliva in the mouth is of great assistance in moistening the
bread while we are chewing it; but it goes farther than this. Some of the
saliva is swallowed before we begin to eat; and this goes down into the
stomach and brings word to the juices there to be ready, for something
is coming. As the food approaches the mouth, a message also is
telegraphed down the nerves to the stomach, which at once actively sets
to work pouring out a digestive juice in readiness, called the "appetite
juice." This shows how important are, not merely a good appetite, but
also attractive appearance and flavor in our food; for if this appetite
juice is not secreted, the food may lie in the stomach for hours before
the proper process of digestion, or melting, begins.
The Salivary Glands. Now, where does this saliva in the mouth come
from? It is poured out from the pouches of the cheeks, and from under
the tongue, by some little living sponges, or juice factories, known as
salivary glands.[2]
[Illustration: 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