THE LAYERS OF THE SKIN
E, epidermis; C, capillaries; D, dermis; F, fat globules and connecting fibres.
We are continually Shedding our Skin. One way in which the skin keeps itself so wonderfully clean and fresh is by continually shedding from its surface showers of these fine, dry, scaly cells, which drop, or are rubbed off, as they dry. This is the reason why no mark, not even a stain or dye, upon the skin, will stay there long; for no matter how deeply it may have soaked into the layers of the pavement-cells, every cell touched by it will ultimately grow up to the surface, dry up, and fall off, carrying the stain with it.
If you want to make a mark on the skin that will be permanent, you have to prick the colors into it so deeply that they will go through the basement layer and reach cells which will not grow toward the surface. This "pricking-in" operation is known as tattooing; and it is as foolish as it is painful, for blood-poisoning and other diseases may be carried into the system in the process.
Perhaps you will wonder why, if you are shedding these scales from all over your surface every day, you don't see them. This is simply because they are so exceedingly small, thin, and delicate, that you cannot see them unless you get a large number of them together; and when you are changing your clothing, bathing, etc., they are rubbed off and float away. If a part of the body has been shut in—as when a broken arm, for instance, is in a cast, which cannot be changed for several weeks—when finally you take off the bandage, you will find inside it spoonfuls—I had almost said handfuls—of fine scales, which have been shed from the skin and held in by the wrappings.
THE GLANDS IN THE SKIN
Sweat Glands. Like all the pavement (epithelial) surfaces of the body, inside and out, the skin has the power of making glands by dipping down little pouches or pockets into the layers below. In the skin, these little gland-pockets are of two kinds, the sweat glands and the hair glands.
The sweat glands are tiny tubes which go twisting down through the different pavement layers, through the basement layer, and right into the coat of fat, which lies just under the skin. The tube of the sweat gland soaks, or picks, out of the blood some of the waste-stuff—just as the kidney tube does in the kidney,—together with a good deal of water and a small amount of delicate oil, and pours them out on the surface of the body in the form of the "sweat," or perspiration.