Читать книгу A Handbook of Health - Woods Hutchinson - Страница 36

The Need of Water in the Body-Engine. If you have ever taken a long railway journey, you will remember that, about every two or three hours, you would stop longer than usual at some station, or switch, for the engine to take in water. No matter how briskly the fire burns in the furnace, or how much good coal you may shovel into it, if there be no water in the boiler above it to expand and make steam, the engine will do no work. And an abundant supply of water is just as necessary in our own bodies, although not used in just the same way as in the engine.

The singular thing about water, both in a locomotive and in our own bodies is that, absolutely necessary as it is, it is neither burned up nor broken down in any way, in making the machine go; so that it gives off no energy, as our food does, but simply changes its form slightly. Exactly the same amount of water, to the ounce, or even the teaspoonful, that is poured into the boiler of an engine, is given off through its funnel and escape-pipes in the form of steam; and precisely the same amount of water which we pour into our stomachs will reappear on the surface of the body again in the form of the vapor from the lungs, the perspiration from the skin, and the water from the kidneys. It goes completely through the engine, or the body, enables the one to work and the other to live, and yet comes out unchanged.

Just how water works in the engine we know—the heat from the furnace changes it into steam, which means that heat expands it, or makes it fill more space. This swelling pushes forward the cylinder that starts the wheels of the engine. The next puff gives them another whirl, and in a few minutes the big locomotive is puffing steadily down the track.

Water is Necessary to Life. Just how water works in the body we do not know, as most of it is not even turned into steam or vapor. But this much we do know, that life cannot exist in the absence of water. Odd as it may seem to us at first sight, ninety-five, yes, ninety-nine per cent of our body cells are water-animals, and can live and grow only when literally swimming in water.

The scaly cells on the surface of our skin, our hair, and the tips of our nails are the only parts of us that live in air. In fact, over five-sixths of the weight and bulk of our bodies is made up of water. Some one has quaintly, but truthfully, described the human body as composed of a few pounds of charcoal, a bushel of air, half a peck of lime, and a couple of handfuls of salt dissolved in four buckets of water. The reason why nearly all our foods, as we have seen, contain such large amounts of water is that they, also, are the results of life—the tissues and products of plants or animals.

Water Frees the Body from Waste Substances. Water in the body, then, is necessary to life itself. But another most important use is to wash out all the waste substances from the different organs and tissues and carry them to the liver, the kidneys, the lungs, and the skin, where they can be burned up and got rid of. We must keep our bodies well flushed with water, just as we should keep a free current of water flowing through our drain-pipes and sewers.

It Keeps the Body from Getting Over-heated. In summer time, or in hot climates the year round, an abundant supply of water is of great importance in keeping the body from becoming overheated, by pouring itself out on the skin in the form of perspiration, and cooling us by evaporation, as we shall see in the chapter on the skin.

THE CHAINED CUP

An "Exchange" for disease germs.

The Meaning of Thirst. None of us who has ever been a mile or more away from a well, or brook, on a hot summer's day needs to be told how necessary water is, for comfort as well as for health. The appetite which we have developed for it—thirst, as we call it—is the most tremendous and powerful craving that we can feel, and the results of water starvation are as serious and as quick in coming as is the keenness of our thirst. Men in fairly good condition, if they are at rest, and not exposed to hardship, and have plenty of water to drink, can survive without food for from two to four weeks; but if deprived of water, they will perish in agony in from two to three days.

We should Drink Three Pints of Water a Day. Although all our foods, either as we find them in the state of nature, or as they come on the table cooked and prepared for eating, contain large quantities of water, this is not enough for the needs of the body; to keep in good health we must also drink in some form about three pints, or six glassfuls, of water in the course of the day. Part of this goes, as you will remember (p. 16), to dissolve the food so that it can be readily absorbed by our body cells in the process of digestion.

WHERE OUR DRINKING WATER COMES FROM

Water Contained in our Food is Pure. Seeing that five-sixths of our food is water, it is clearly of the greatest importance that that water should be pure. That part of our water supply which we get in and with our foods is fortunately, for the most part, almost perfectly pure, having been specially filtered by the plants or animals which originally drank it, or having been boiled in the process of cooking.

THE SPOUTING FOUNTAIN

Where no lips need touch the cup.

Water is Always in Motion. The part of our water supply which we take directly, in the form of drinking water, is, however, unfortunately anything but free from danger of impurities. The greatest difficulty with water is that it will not "stay put"—it is continually on the move. The same perpetual circulation, with change of form, but without loss of substance, which is taking place in the engine and in our bodies, is taking place in the world around us. The water from the ocean, the lakes, and the rivers is continually evaporating under the heat of the sun and rising in the form of vapor, or invisible steam, into the air. There it becomes cooler, and forms the clouds; and when these are cooled a little more, the vapor changes into drops of water and pours down as rain, or, if the droplets freeze, as snow or hail. The rain falls upon the leaves of the trees and the spears of the grass, or the thirsty plowed ground, soaks down into the soil and "seeps" or drains gradually into the streams and rivers, and down these into the lakes and oceans, to be again pumped up by the sun. All we can do is to catch what we need of it, "on the run," somewhere in the earthy part of its circuit.

Why our Drinking Water is Likely to be Impure. Every drop of water that we drink or use, fell somewhere on the surface of the earth, in the form of rain or snow; and if we wish to find out whether it is pure and safe, we must trace its course through the soil, or the streams, from the point where it fell. Our drinking water has literally washed "all outdoors" before it reaches us, and what it may have picked up in that washing makes the possibilities of its danger.

As it falls from the skies, it is perfectly pure—except in large cities or manufacturing centres, where rain water contains small amounts of soot, smoke-acids, and dust, but even these are in such small amounts as to be practically harmless. But the moment it reaches the ground, it begins to soak up something out of everything that it touches; and here our dangers begin.

Risks from Leaf Mould. Practically the whole surface of the earth is covered with some form of vegetation—grass, trees, or other green plants. These dying down and decaying year after year, form a layer of vegetable mould such as you can readily scratch up on the surface of the ground in a forest or old meadow; this is known as leaf mould, or humus. As the water soaks through this mould, it becomes loaded with decaying vegetable matter, which it carries with it down into the soil. Most of this, fortunately, is comparatively harmless to the human digestion. But some of this vegetable matter, such as we find in the water from bogs or swamps, or even heavy forests, will sometimes upset the digestion; hence, the natural dislike that we have for water with a marshy, or "weedy," taste.

NATURE'S FILTER-BED

The spring water is pure; the brook may gather infection as it goes.

Nature's Filter-Bed. When, however, this peaty water soaks on down through the grass, roots, and leaf mold, into the soil, it comes in contact with Nature's great filter-bed—the second place in the circuit where the water is again made perfectly pure. This filter-bed consists of a layer of more or less spongy, porous soil, or earth, swarming with millions of tiny vegetable germs known as bacteria. These eagerly pick out all the decaying vegetable substances of the water and feed upon them, changing them into harmless carbon dioxid water, and small amounts of ammonia. Not only will this filter-bed, or spongy mat of bacteria, burn up and remove all traces of vegetable decay, but if the rain happens to have soaked through the decaying body of a bird or animal or insect, the bacteria will just as eagerly feed upon these animal substances and change them into harmless gases and salts.[13]

By the time the rain water has reached the deeper layers of the soil, it is again perfectly pure and has also, in seeping through the soil, picked up certain mineral salts (such as calcium, sodium, and magnesium) which are of use in the body; so that in an open or thinly settled country, the water in streams, rivers, and lakes is usually fairly pure and quite wholesome. That is why, in ancient times, the great majority of villages and towns and camps were situated on the bank of some stream, where a supply of water could easily be obtained.