FOOTNOTES
The term salts includes, as will be explained later, a large number of substances, like ordinary table salt, baking soda, and the laxative salts.
There are three pairs of these: one just below the ears and behind the angles of the jaw, known as the parotid; one under the middle of the lower jaw known as the submaxillary; and a small pair just under the tip of the tongue, called the sublingual. These glands have grown up from the very simplest of beginnings. At first there was just a little pocketing or pouching down of the mucous lining, like the finger of a glove; then a couple of smaller hollow fingers budded off from the bottom of the first finger; then four smaller fingers from the bottom of these; and so on, until a regular little hollow tree or shrub of these tiny tubes was built up, all discharging through the original hollow stem, which has now become what we call the duct of the gland. Every secreting gland in the body—the stomach (or peptic) glands, the salivary glands, the liver, the pancreas—is built up upon this simple plan. The saliva and the juice of the pancreas and that of the liver (bile) are alkaline, as are also the blood and most juices of the body. The stomach juice is acid, as also are the urine and the perspiration.
It is wonderfully elastic and constantly changing in size, contracting till it will scarcely hold a quart when empty, and expanding, as food or drink is put into it, until it will easily hold two quarts, or even a gallon or more when greatly distended, as by gas.
If you take some pepsin which has been extracted from the stomach of a pig or a calf, melt it in water in a glass tube, then drop one or two little pieces of meat or hard-boiled white of egg into it, you can see them slowly melt away like sugar in a cup of coffee. If you add a few drops of hydrochloric acid, the melting will go on much faster; and if you warm up the tube to about the heat of the body, it will proceed faster still. So nature knew just what she was doing when she provided pepsin and acid and warmth in the stomach.
The liver and the bile are more fully described in chapter [XVII].
Tiny plant cells, known also as germs, which cause fermentation, decay, and many diseases.
On this account, they are often spoken of as carbohydrates, or "carbon-water stuffs."
See page [11].
Pemmican is a sort of "canned beef" made originally out of the best parts of venison and buffalo-meat. This is boiled, and packed into skin bags; then melted fat is poured in, so as to fill up all the chinks and form a thick layer over the surface. It is now made of beef packed in canvas bags, and is much used by polar expeditions and Alaskan miners.
As vegetables and fruit are bulky and likely to spoil, on the long voyages of sailing vessels before steamships were invented bottles of the juice of limes (a small kind of lemon) were added, instead, to the hard-tack and "salt-horse" of the ship's stores. Because of this custom, the long-voyage merchantmen who carried cargoes round the Horn or the Cape were for years nicknamed "Lime-juicers."
For meats a fourth method may be used—broiling, which for flavor and wholesomeness is superior to any other, but requires a special and rather expensive type of clear, hot fire and a high degree of skill.
Whenever lunches are brought by children, or the school-lunch is a problem, if possible equip a spare room with a gas or a coal stove, sink, tables, chairs, necessary dishes, etc., and let classes under direction of teacher take turns in purchasing food supplies for lunch; cooking and serving lunch; planning dietaries with reference to balanced nutrition, digestibility, and cheapness; washing pots, pans, and dishes; cleaning kitchen; protecting and storing foods; finding risks of spoiling, contamination, infection, fly-visiting; and practicing other forms of kitchen hygiene.
These gases and salts are eagerly sucked up by the roots of plants, so that the soil bacteria are our best friends, changing poisonous decaying things into harmless plant-foods. They are the chief secret of the fertility of a soil; and the more there are of them the richer a soil is.
This makes fourteen times as many deaths from typhoid in proportion to the population as occur in Germany.
New York City, for instance, goes forty miles up into the hills to the great Croton reservoir for its water supply; and as this is proving insufficient, is preparing to go ninety-five miles up into the Ramapo Hills to secure control of a whole country-side for a permanent source of supply. Portland, Oregon, nearly twenty years ago, with then a population of some 75,000, built an aqueduct sixty miles up into the mountains to a lake on the side of Mt. Hood, and has reaped the advantages of its foresight ever since, in a low death rate and a rapid growth (200,000 in 1910), as well as a financial profit on its investment. Los Angeles, California, is preparing to build an aqueduct a hundred and thirty miles, and tunnel two mountain ranges in order to reach an inexhaustible supply of water.
Of late, currents of electricity are passed through the water (setting free oxygen or ozone) which make the purifying of it much more rapid and complete.
It is, however, often considered safer to pass the water through still another filter bed, consisting of layers of charcoal, which has the power of gathering oxygen in its pores, to attack and oxidize, or burn up, the remaining impurities in the water. A sort of scum forms over the surface of the last and finest bed of sand or charcoal, and if this scum is not too frequently removed, though it makes the filtering slower, the water comes out purer. On examining this scum, we find it to consist of a thick mat of our old friends, the purifying bacteria of the soil. So that the last step of our artificial filtration is simply an imitation of nature's great filter-bed.
Several streams emptying into the Ohio River from a thickly settled region are said to be actually pumped out into waterworks systems, used for drinking, washing, and manufacturing, and run back into the river again through sewers by the different cities along its banks, at such frequent intervals that every drop of water in them passes through waterworks systems and sewers three times before it reaches the mouth of the stream.
This nitrogen, though of no value for breathing, is of great value as a food, forming, as we have seen, an important part of all meats, or proteins, which build the tissues of our bodies. It can, however, be taken from the air only with great difficulty, by a very roundabout route; the bacteria of the soil eat it first, then they pass it on as food to the roots of plants; animals eat plants, and we eat the animals, and thus get most of our nitrogen.
Hairs are of value chiefly as protection against cold and wet, although we have got rid of them and substituted clothing for this purpose, except on the top of our heads; but their roots also are very richly supplied with nerves so that they form almost a sort of feelers, or organs of sense. Many animals that move about much in the dark, like cats and bats, for instance, have their lips or faces studded with long, delicate, stiff hairs called whiskers, which act in this way and prevent their bumping into objects in the dark. And it is probable that the bristling of the hair on a dog's back, when he is angry or frightened, is in part for this purpose—to enable him to slip aside and dodge a blow, even after it has touched the ends of the hairs. This great sensitiveness of the hair roots is what makes it hurt so when any one pulls your hair.
See the diagram of the skin on page [171].
You can easily test this by a very simple experiment. Take a pair of dividers; or, if you haven't these, a couple of long pins or needles will do. Set them with their points a quarter of an inch apart. Then touch these points, first closing your eyes, so that you will not be able to see them, to the tip of one of your fingers, and you will readily feel that two points touch the skin. Turn your hand over and touch the back of it with the two points, and they will feel like one point. Carry the test further, over other parts of the body, and you will find that they are much less sensitive; thus you will find that at the back of the neck, or over the shoulder-blades, you will have to put the points nearly an inch apart before you can tell that there are two of them. This simply means that you have to touch two separate touch bulbs before you can get the idea of "two-ness." As these bulbs are an inch or more apart in the skin of the back, you have to spread the points of the dividers that distance. You can also prove that the touching of two nerve-buds gives the idea of "two-ness" by crossing two of your fingers and placing a pea, or small round piece of chalk, between their crossed tips. If you close your eyes and roll the pea on the table, or desk, you will think you have two peas between your fingers.
The muscle does not get any bigger when it contracts, as was at one time supposed; if you were to plunge it into a bath of water, and then cause it to contract, you would find that it did not raise the level of the water, showing that it was of exactly the same size as before, having lost as much in length as it gained in thickness.
In the leg below the knee, and in the forearm, we have two groups of "benders" or flexors, and "straighteners" or extensors, as in the upper arm and leg, only slenderer and more numerous. They taper down into cord-like tendons at the wrist and ankle to fasten and to pull the hands and feet "open" and "shut," just as do the strings in the legs and arms of a puppet or mechanical doll, or the sinews in the foot of a chicken.
You can easily prove that a bone is made up of living tissue soaked and stiffened with lime, by putting it into a jar filled with weak acid. This will gradually dissolve and melt out the lime salts, and then you will find that the bone has lost three-fourths of its weight and that what remains of it is so soft and flexible that it can be bent, or even tied into a knot.
The hollow spaces in the bones of birds, however, are filled with air, which makes them lighter for flying.
To give you an idea of what real things nerve-trunks are, this sciatic nerve is as large as a small clothes-line, or, more accurately, as a carpenter's lead pencil, and so strong that when the surgeon cuts down upon it and stretches it to cure a very bad case of sciatica, he can lift the lower half of the body clear of the table by it. This strength, of course, is not due to the nerve-fibres and cells themselves but to the tough, fibrous sheath, or covering, with which all the nerves that run outside of the brain and spinal cord are covered and coated. The spinal cord, though it is between one-half and three-fourths of an inch across, or about the size of an ordinary blackboard pointer, has little or none of this fibrous tissue in it, and is very soft and delicate, easily torn when its bony case is broken; hence its old name, the spinal marrow, from its apparent resemblance to the marrow, or soft fat, in the hollow of a bone.
Some of these coal-tar remedies are Acetanilid, and Antipyrin, and Phenacetin.
To show in how many different ways nature may carry out the same purpose, the smelling organs in insects, lobsters, and crabs are on the ends and sides of tiny feelers, which they wave about; and the eyes in lobsters, crawfish, and snails, are on the ends of stalks, which they thrust about in all directions as a burglar handles a bull's-eye lantern. Snakes "hear," or catch the sound-waves, with their flickering, forked tongues; and grasshoppers and locusts have "ear-drums" on the sides of their chests.
These are called the recti or "straight" muscles, upper, lower, inner, and outer, according to their position. Then, to roll the eye round and round, there are two little muscles, one above and one below, which run "crosswise" of the orbit, called the upper and lower oblique muscles.
The retina is chiefly made up of a great number of fine little nerve cells called, from their shape, the rods and cones. These are kept soaked in a colored fluid called the retinal purple, which changes under the influence of light, somewhat in the same way that the film on a photographic plate does, thus forming pictures, which are translated by the rods and cones and telegraphed along the fibres of the optic nerve to the brain. Naturally, all parts of the retina are not equally sensitive to light; its centre, which is directly opposite the pupil of the eye, is far the most so, while those around the rim of the cup are dull. This is why, when you are looking, say at some one's face across the room, only the face and a few inches around it are seen perfectly clear and sharp, while the rest of the room is seen only vaguely.
As the inside of the eye is dark, or comparatively so, the pupil, or little opening in the centre of the iris, looks black, and was at one time supposed to be a solid body instead of a hole. You can easily watch the pupil changing in size, according to the brightness of the light, from a mere pin-point in very bright sunlight or gaslight, up to the size of the butt-end of a lead pencil in the dark or in a dim light.
This change in size is very simply but ingeniously carried out by two sets of tiny muscles. One set of these muscles runs in a ring right around the pupil; and when they shorten, the opening is contracted or narrowed. The other set runs outward through the iris like the spokes of a wheel; and when they shorten, they pull the pupil open. If anyone has had "drops" (atropin) put into his eyes in order to have them fitted with glasses, he will know what a disagreeably dazzling thing it is to have the pupil permanently enlarged, so that it cannot contract in a bright light.
A famous violin-maker who lived about 200 years ago in Cremona, Italy. Fifty thousand dollars has been asked for an unusually choice "Strad."