Health Shown by the Color of the Nails. Your nails and your lips are not really any redder, or pinker, than the rest of your skin; but the cells forming them are clear and transparent and allow the red blood to show through. This is why we often look at the nails and lips to see what the color of the blood is like, and how well or badly it is circulating. If the blood is _anemic_, or thin, then both lips and nails are pale and dull. If the blood is healthy and the circulation good, then the nails are pink, and the lips clear red. If, on the other hand, the circulation is bad, as in some forms of lung disease and heart disease, so that the blood is loaded with carbonic acid until it is blue and dark, then the lips may become purplish or dark blue, and the finger nails nearly the same color.

THE BLOOD-MESH OF THE SKIN

The Blood Vessels under the Skin. Not merely the nails and the lips, but the whole surface of the skin is underlaid with a thick mat, or network, of blood vessels. These vessels are all quite small, so that a cut has to go down completely through the skin, and generally well down into the muscles, before it will reach any blood vessel which will bleed at a dangerous rate. But there are so many of them, and they cover such a wide surface throughout the body, that they are actually capable of holding, at one time, nearly one-tenth of all the blood in the body.

This "water-jacket" coat of tiny blood vessels all over our body has some very important uses: It allows the heart to pump large amounts of blood out to the surface to be purified by the sweat glands, and to breathe out a little of its carbon dioxid and other gas-poisons.

The Skin as a Heat Regulator. Heat, as well as waste, is given off by the blood when it is poured out to the surface; so another most important use of the skin is as a heat regulator. As we have already seen, every movement which we make with our muscles, whether of arms and limbs, heart, or food tube, causes heat to be given off. We very well know, when we work hard at anything, we are likely to "get warmed up."

Although a certain amount of this heat is necessary to our bodily health, too much of it is very dangerous.

Just as it is best for the temperature, or heat, of a room to be at about a certain level, somewhere from 60 to 70 F., so it is best for the interior of our bodies to be kept at about a certain heat. This, as we can show by putting a little gla.s.s thermometer under the tongue, or in the armpit, and holding it there for a few minutes, is a little over 98 F. (98.4 to be exact); and this we call "body heat," or "blood heat," or "normal temperature." Our body cells are, in one way, a very delicate and sensitive sort of hot-house plants, though tough enough in other respects. Whenever our body heat goes down more than five or six degrees, or up more than two or three degrees, then trouble at once begins. If our temperature goes down, as from cold or starvation, we begin to be drowsy and weak, and finally die. If, on the other hand, our temperature climbs up two, three, or four degrees, then we begin to be dizzy and suffer from headache and say we have "a fever."

A fever, or rise of temperature, that can be noted with a thermometer, is usually due to disease germs of some sort in the body; and most of the discomfort that we suffer is really due more to the poisons (toxins) of the germs than to the mere increase of heat, though this alone will finally work serious damage. However, as we well know from repeated experience, we need only to run or work hard in the sun for a comparatively short time to make ourselves quite hot enough to be very uncomfortable; and if we had no way to relieve ourselves by getting rid of some of this heat, we should either have to stop work at once, or become seriously ill. This relief, however, is just what nature has provided for in this thick coat of blood vessels in our skin; it enables us to throw great quant.i.ties of blood out to the surface where it can get rid of, or, as the scientists say, "radiate," its heat. This cooling process is hastened by the evaporation of the perspiration poured out at the same time, as we have seen.

One of the chief things in training for athletics is teaching our skin and heart together to get rid of the heat made by our muscles, as fast, or nearly as fast, as we make it, thus enabling us to keep on running, or working, without discomfort. As soon as we stop running, or working, the heart begins to slow down, the blood vessels in the skin contract and diminish in size, the flush fades, and we begin to cool off. We are not making either as much heat or as much waste as we were, and hence do not need to get rid of so much through our skins.

When we feel cold, just the opposite kinds of change occur in the skin.

The blood vessels in the skin contract so as to keep as much of our warm blood as possible in the deeper parts of our body, and prevent its losing heat. As blood showing through the pavement-layer of the skin is what gives us our color, or complexion, our skin becomes pale and pasty-looking; and if all the blood is driven in from the surface, our lips and finger nails will become blue with cold. Here again, by changes in the skin, nature is simply trying to protect herself from the loss of too much heat.

If we exercise briskly, or eat a good warm meal, and thus make more heat inside of our body, then there is no longer any need to save its surface loss in this way; and the blood vessels in our skin fill up, the heart pumps harder, and the warm, rich color comes back to our faces and lips and finger nails.

So perfectly and wonderfully does this skin mesh of ours work, by increasing or preventing the loss of heat, that it is almost impossible to put a healthy man under conditions that will raise or lower his temperature more than about a degree, that is to say, about one per cent above, or below, its healthful level. Men studying this power of the skin have shut themselves into chambers, or little rooms, built like ovens, with a fire in the wall or under the floor, and found that if they had plenty of water to drink and perspired freely, they could stand a temperature of over 150 F. without great discomfort and without raising the temperature of their own bodies more than about one degree.

If, however, the air in the chamber was moistened with the vapor of water, or steam, so that the perspiration could no longer evaporate freely from the surface of their bodies, then they could not stand a temperature much above 108 or 110 without discomfort.

Other men, who were trained athletes, have been put to work in a closed chamber, at very vigorous muscular exercise, so as to make them perspire freely. But while a thermometer placed in that chamber showed that the men were giving off enormous amounts of heat to the air around them, another thermometer placed under their tongues showed that they were raising the temperature of their own bodies only about half a degree.

One man, however, happened to try this test one morning when he was not feeling very well, and didn't perspire properly, and the thermometer under his tongue went up nearly four degrees.

THE NERVES IN THE SKIN

How We Tell Things from Touch, and Feel Heat and Cold and Pain. Last of all, the skin is the princ.i.p.al organ of the sense of touch, and also of the "temperature sense"--the sense of heat and cold--and of the sense that feels pain. All these feelings are attended to by little bulbs lying in the deeper part of the skin and forming the tips of tiny nerve twigs,[20] which run inward to join larger nerve branches and finally reach the spinal cord. There are millions of these little bulbs scattered all over the surface of the skin, but they are very much thicker and more numerous in some parts than in others; and that is why, as you have often noticed, certain parts of the skin are more sensitive than others. They are thickest, for instance, on the tips of our fingers and on our lips, and fewest over the back of the neck and shoulders, and across the lower part of the hips.[21]

For a long time, it was supposed that all these little nerve-bulbs in the skin did the same kind of work, because they looked, under the microscope, exactly alike; but it was found that they divide the work up among them, so that some of them give their entire attention to heat, and others to cold, others to touch, and others again to pain. So carefully has the work been mapped out among them that they report to different centres in the brain and spinal cord, so that we now understand why, in diseases which happen to attack one or other of these centres, we may lose our sense of heat and cold, as in that terrible disease, _leprosy_; or our sense of touch, as in _paralysis_; or we may even, in some very rare cases, lose our sense of pain, and yet have all our other senses perfect.

FOOTNOTES:

[19] Hairs are of value chiefly as protection against cold and wet, although we have got rid of them and subst.i.tuted 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 b.u.mping 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.

[20] See the diagram of the skin on page 171.

[21] 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.

CHAPTER XVI

HOW TO KEEP THE SKIN HEALTHY

CLOTHING

Clothes should be Loose and Comfortable. Man is the only animal that has no natural suit of clothing. Birds have feathers, and animals have fur, or hair, which they shed in summer and thicken up in winter without even thinking about it, so that they do not have to bother with either overcoats or flannels. The wise men say that man originally had a full suit of hair like other animals, and that he gradually got rid of it, as he became human. Whether this be true or not, the fact remains that he has none now; and consequently he must invent and manufacture something to take its place.

Originally, in the time of our savage ancestors, clothing was worn chiefly as protection from cold at night, so that all the earlier forms of clothing were of a more or less blanket-or cloak-like form, and wrapped, or swathed, the whole body without fitting closely to the limbs. It is interesting to remember this fact, because even our most highly civilized forms of clothing still show this same tendency. The skirt, for instance, is simply a survival of the lower end of the blanket, which has never been cut down to fit the limbs.

The principles upon which garments should be built are two: First, they should fit closely enough to the body and limbs to protect them from either injury or cold, even while free activity of every sort is allowed--you could not wrestle in a blanket or run very far in a sack.

Second, they should be thick enough to protect us from cold, and yet at the same time porous enough not to interfere with the natural breathing and ventilating of the skin. A garment should be as loose as possible without interfering with our movements, and as free and as light as can be worn with reasonable warmth and protection. The less clothing you can wear and be comfortable, the better.

We should particularly avoid binding or cramping the chest and the hips and waist. If clothing is too tight about the chest, it interferes both with free movement of the arms and, what is even more important, with the breathing movements of the chest. If too tight about the waist and hips, it badly cripples the lower limbs and interferes with the proper movements of the diaphragm in breathing, and with the pa.s.sage of the food and the blood through the bowels.

Your instincts are perfectly right that make you dislike to be squeezed or pinched or cramped in any way, or at any point, by your clothing; and if you will only follow these instincts all through your lives, you will be far healthier and happier.

The Texture of Clothing. Just as for ages we have experimented with different kinds of food, so we have with different kinds of material for clothing. We have used the skins of animals; mats woven out of leaves and gra.s.ses; the feathers of birds; the skins of fishes; cloths made of wool and of cotton; and even the coc.o.o.n spun by certain caterpillars, which we call _silk_. But of all these materials, practically only two have stood the test of the ages and proved themselves the most suitable and best all-round clothing materials--wool and cotton.

Woolen cloth, woven from the fleece of sheep or goats or camels or llamas or alpacas, has three great advantages, which make it _the_ outside clothing of the human species. First, it is sufficiently tough and lasting to withstand rips and tugs and ordinary wear and tear; second, it is warm--that is, it retains well the body heat; and third, it is porous, so that it will allow gases and perspiration from the surface of the body to pa.s.s through it in one direction, and air for the skin to breathe, in the other.

[Ill.u.s.tration: RESULTS OF TIGHT CLOTHING

(1) The normal thorax. (2) The thorax and organs cramped and lifted by pressure of the clothing. (From an X-ray photograph.--After d.i.c.kinson.)]

No clothing, of course,--not even fur,--has any warmth in itself; it simply has the power of retaining, or keeping in, the warmth of the body that it covers. The best and most effective way of retaining the body warmth is to surround the body with a layer of dead, or still, air, which is the best non-conductor of heat known. Hence, porous garments, like loosely-woven flannels, blankets, and other woolen cloths, are warm because they contain or hold large amounts of air in their spongy mesh.

The reason why furs are so warm is that their soft, furry under-hairs, or "pelt" as the furriers call it, entangle and hold an enormous amount of air. The fur of ordinary sealskin, for instance, is about half an inch deep; and _ninety per cent_ of this half-inch is air. If you wet it, its fur "slicks down" to almost nothing, although the most drenching wetting will not wash all the air out of it, but still leaves a dry layer next to the skin. The fur of mink skin, c.o.o.n skin, or wolf skin, is an inch thick; and nearly eighty per cent of this thickness is air.

The great advantage for clothing purposes of wool over fur is that the wool is porous through and through, while the fur is borne upon, and backed by, a layer of leather--the skin of the animal upon which it grew--which layer, after tanning and curing, becomes almost absolutely air-tight.

As a matter of fact, furs are worn mostly for display and are most unwholesome and undesirable garments. The only real excuse for their use, save for ornament in small pieces or narrow strips, is on long, cold rides in the winter, and among lumbermen, frontiersmen, and explorers. They hold in every particle of perspiration and poisonous gas thrown off by the skin, and if worn constantly, make it pale, weak, and flabby; and the moment we take them off, we take cold.

For outer garments and general wear, nothing yet has been discovered equal to wool, particularly at the cooler times of the year. But for under wear, in the hotter seasons and climates, wool has certain disadvantages. It is likely to be rough and tickling to most skins, which makes it uncomfortable, especially in warm weather. It is also difficult and troublesome to wash woolens without shrinking them; and, as soon as they do shrink, not only do they become uncomfortably tight, but the natural pores in them which make them so valuable close up, and they become almost air-tight. Finally, when loaded with perspiration, woolens easily become offensive, so that they must be frequently changed and washed; and as they are also high in price, it is easily seen that there are practical drawbacks to their use.

Cotton is much softer and pleasanter to the skin than wool, is cooler in hot weather, is much cheaper, and is very easily washed without losing either its shape or its porousness. It can be so woven as to be almost as porous as wool, and to retain that porousness even when saturated with perspiration. It does not soak up and retain the oils and odors of perspiration in the way that wool does; and on the whole, for under wear, and for general wear at the warm seasons of the year, it is not only more comfortable, but far more healthful, than wool. Persons of fair health and reasonably vigorous outdoor habits, whose skins are well bathed and ventilated, can wear properly woven cotton or linen undergarments the whole year round with perfect safety.

[Ill.u.s.tration: A COMFORTABLE DRESS FOR OUTDOOR STUDY IN COLD WEATHER

The thick bags pulled up to the shoulders keep the body surrounded by a layer of warm air.]

Linen and silk both make admirable and healthful under wear, if woven with a properly porous mesh. Linen has the advantage of remaining more porous than cotton, when moist with perspiration. But for healthy people they have no advantages over cotton that are not offset by their higher prices.

BATHS AND BATHING

Bathing as a Means of Cleanliness. It has been said that one of the reasons why man lost his hairy coat was that he might be able to wash himself better and keep cleaner. However this may be, he has to wash a great deal oftener than other animals, most of whom get along very well with currying, licking, and other forms of dry washes, and an occasional swim in a river or lake.

You can readily see how necessary for us washing is, when you remember the quarts of watery perspiration, which are poured out upon our skins every day, and the oily and other waste matters, some of them poisons, which the perspiration leaves upon our skins. Especially is some means of washing necessary when the free evaporation of perspiration and the free breathing of the skin has been interfered with by clothing which is water-tight or too thick.