First Book in Physiology and Hygiene

by John Harvey Kellogg

CHAPTER XV.

THE SKIN AND WHAT IT DOES.

1. The Skin.—The skin is the covering of the body. It fits so exactly that it has the precise shape of the body, like a closely fitting garment. If you will take up a little fold of the skin you will see that it can be stretched like a piece of india-rubber. Like rubber, when it is released it quickly contracts and appears as before.

2. The Bark of Trees.—Did you ever peel the bark off of a young tree? If so, you have noticed that there were really two barks, an outer bark, as thin as paper, through which you could almost see, and an inner and much thicker bark, which lay next to the wood of the tree. You can peel the outer bark off without doing the tree much harm. Indeed, if you will notice some of the fruit or shade trees in the yard, at home, you will see that the outer bark of the tree peels itself off, a little at a time, and that new bark grows in its place. If you tear off the inner bark, however, it will injure the tree. It will make it bleed, or cause the sap to run. The sap is the blood of the tree. The bark is the skin of the tree. When the bare place heals over, an ugly scar will be left.

3. The Cuticle.—Our bodies, like trees, have two skins, or really one skin with an outer and an inner layer. When a person burns himself so as to make a blister, the outer skin, called the cuticle, is separated from the inner by a quantity of water or serum poured out from the blood. This causes the blister to rise above the surrounding skin. If you puncture the blister the water runs out. Now we may easily remove the cuticle and examine it. The cuticle, we shall find, looks very much like the skin which lines the inside of an egg-shell, and it is almost as thin.

4. The cuticle is very thin in most parts of the body, but in some places, as the palms of the hands and the soles of the feet, it is quite thick. This is because these parts of the skin come in contact with objects in such a way as to be liable to injury if not thus protected. The cuticle has no blood-vessels and very few nerves. With a fine needle and thread you can easily take a stitch in it without making it bleed or causing any pain.

5. The Pigment.—The under side of the cuticle is colored by little particles of pigment or coloring matter. The color of this pigment differs in different races. In the negro, the color of the pigment is black. In some races the pigment is brown. In white persons there is very little pigment, and in some persons, called albinos, there is none at all.

6. The Inner or True Skin.—The inner skin, like the inner bark of a tree, is much thicker than the outer skin. It is much more important, and for this reason is sometimes called the true skin. It contains nerves and blood-vessels.

SKIN OF PALM OF
HAND MAGNIFIED.

7. The Sweat Glands.—If you look at the palm of the hand you will see many coarse lines, and by looking much closer you will see that the palm is completely covered with very fine ridges and furrows. Now, if you examine these ridges with a magnifying-glass, you will find arranged along each ridge a number of little dark spots. Each of these points is the mouth of a very small tube. This is called a sweat duct. These ducts run down through both the outer and inner layers of the skin. At the under side of the true skin the end of the tube is rolled up in a coil, as you can see by looking at the illustration on the following page. The coiled parts of the tubes are called sweat glands, because they separate from the blood the fluid which we call sweat or perspiration.

8. The Oil Glands.—There are other little glands in the skin which make fat or oil. The oil is poured out upon the skin to keep it soft and smooth.

THE STRUCTURE OF THE SKIN.

9. The Hair.—There are some curious little pockets in the skin. Out of each of these pockets grows a hair. On some parts of the body the hairs are coarse and long; on other parts they are fine and short.

10. Many of the ducts leading from the oil glands open into the pockets or pouches from which the hairs grow. The oil makes the hair soft and glossy. Nature has thus provided an excellent means for oiling the hair.

11. The hair is chiefly useful as a protection. It is also an ornament.

12. The Nails.—The nails of the fingers and the toes grow out of little pockets in the skin just as the hairs do. Both the hair and the nails are really parts of the outer skin, which is curiously changed and hardened. The nails lie upon the surface of the true skin and grow from the under side as well as from the little fold of skin at the root of the nail. They are made to give firmness and protection to the ends of the fingers and toes. The nails of the fingers are also useful in picking up small objects and in many other ways.

13. Uses of the Skin.—The skin is useful in several ways:

(1) It Removes Waste.—The sweat glands and ducts are constantly at work removing from the blood particles which have been worn out and can be of no further use. If we get very warm, or if we run or work very hard, the skin becomes wet with sweat. In a little while, if we stop to rest, the sweat is all gone. What becomes of it? You say it dries up, which means that it has passed off into the air. Sweating is going on all the time, but we do not sweat so much when we are quiet and are not too warm, and so the sweat dries up as fast as it is produced, and we do not see it. Nearly a quart of sweat escapes from the skin daily.

(2) Breathing through the Skin.—We breathe to a slight extent through the skin. There are some lower animals which breathe with their skins altogether. A frog can breathe with its skin so well that it can live for some time after its lungs have been removed. Breathing is an important part of the work of the skin, and we should be careful, by keeping it clean and healthy, to give it a good chance to breathe all that it can.

(3) The Skin Absorbs.—The skin absorbs many substances which come in contact with it, and hence should be kept clean. If the foul substances which are removed in the sweat are allowed to remain upon the skin, they may be taken back into the system and thus do much harm.

(4) The Skin has Feeling.—When anything touches the skin we know it by the feeling. We can tell a great many things about objects by feeling of them. If we happen to stick a pin into the skin we feel pain. We are also able to tell the difference between things which are hot and those which are cold. Thus the sense of feeling which the skin has is very useful to us.

(5) The Skin Protects the Body.—The skin is a natural clothing which protects us much better than any other kind of clothing could. It is so soft and pliable that it cannot hurt the most delicate part which it covers, yet it is very strong and tough.