The skin is the protective covering of the body, and it has an interesting and somewhat complex function. In the first place, it is a sort of envelope, just as the skin of the plum or apple is an envelope to the pulp beneath. It thus prevents the entrance of germs to the tissues it covers. The bruised skin of the ripe peach cannot withstand the microbes which set up degenerative changes in the pulp beneath. In the same way, it is through a cut or an abrasion that microbes find their way into the body. An interesting example of this is the entrance of tetanus bacillus, or the microbe of "lock jaw," as the result of an accident on a dusty highway, as sometimes happens if the skin is injured and dust gets in. The skin has also to do with the regulation of body heat, and with the important function of evaporation, by means of which waste products are eliminated.
These functions we shall consider after we have studied the structure of the skin. As we see it, the skin is a soft, smooth membranous material, which can adapt itself to the different parts of the body and to its movements. That is because it is "elastic." It can stretch to a considerable extent without losing its natural shape. The skin, to the naked eye, appears to be fairly uniform in thickness, although we can see that it is finer over such parts of the body as the neck and face and thicker where there is more pressure, as on the palms of the hands and soles of the feet. If the skin is examined under the microscope, it can be seen that it is very complex in structure. Even without a microscope it can be demonstrated that there are two main layers of skin, the outer skin, epidermis, or cuticle, and the inner, or true, skin. The true skin, or dermis, is very sensitive, because it contains a large number of tiny nerve fibres and nerve endings. Almost the whole of the skin is covered with hairs, which consist of a bulb lying under the true skin.
The epidermis consists of several layers of fine flat scales, arranged like tiles on the roof, which are constantly being thrown off from the surface of the body as scurf. The cuticle contains no blood-vessels or nerve fibres, so that it is insensitive. The true skin, however, is richly supplied with nerves and "nerve endings.' These are "touch corpuscles," which receive the sensations of heat, cold, or pain, and transmit them to the nerves, and thence to the brain. The dermis is also rich in glands, of which there are two kinds: (I) the sebaceous glands, which secrete a fatty or oily substance to keep the skin soft and smooth; (2) the sweat glands, which excrete water and waste products from the body in the form of perspiration.
If our eyesight were sufficiently keen to observe the minute structure of the skin, we could easily see that all over the body there are tiny holes, the openings of the sweat glands. These pores lead down into minute tubes about a quarter of an inch long which, below, are twisted into little knots, or glands, which are in contact with tiny capillary blood-vessels. These blood-vessels are, as has before been said, very thinly walled, and substances pass through them directly into the sweat glands, and thence, by means of the sweat ducts, or tubes, to the surface of the body. There are two or three millions of these sweat glands in the skin, and if they are kept in a healthy condition they get rid of an immense amount of waste substances from the body. There are three main excretory organs of the body:
1. The lungs, which give off carbonic acid, water, and various organic waste matters.
2. The kidneys are also important excretory organs, which draw off water and other waste matters from the blood, which passes to the bladder.
It can thus be seen that if the skin is not healthy and in good working condition more work is thrown upon the kidneys and lungs, and if these are unable to take on increased work, waste substances collect in the body and all sorts of ills of the flesh, such as gout, are liable to occur. To keep the skin active, the home nurse must realise that thorough cleanliness is essential. If the body is washed once daily, the pores of the sweat glands are kept open. Otherwise, scurf, which the skin is shedding, and the dust of the atmosphere form with the perspiration a kind of crust which chokes up the pores.
The second great function of the skin has to do with the regulation of temperature. The normal temperature of the body is 98 4° Fahr. By muscular exercise and by the ingestion of food, heat is produced. This heat is distributed over the body by the blood. Thus, the temperature of the whole body is kept uniform, even if by rapid movement of the legs or arms heat is generated in one part. The circulation of the blood throughout the body, from one side of the heart to the other, takes about half a minute, and this fact provides rapid distribution of heat.
The blood passes to the capillary vessels on the surface of the skin, which become very much dilated when a person is "over-heated," or in hot weather. Now, when these surface blood-vessels of the skin are dilated and filled with blood, the excess of heat passes into the sweat glands, which become very active, owing to the increased supply of blood in the part. These rapidly form perspiration, which passes through the sweat tubes to the surface of the body; and when the skin is very hot, the perspiration appears in beads of moisture. At the same time, of course, the lungs are doing increased work, and heat is given off in the breath. In cold weather, on the other hand, when the body is chilled, the blood-vessels in the skin contract, and the blood is driven into the interior of the body, thus preventing loss of heat. This function of the skin to contract under the influence of cold and to dilate under the influence of heat, is to a certain extent lost in civilised communities. For one thing, we cover up the body with clothes, and thus make it more sensitive to cold, and less capable of fulfilling its normal function. In more primitive races, the human body does not feel cold to the same extent that we do.
"Me all face," said the American Indian who was asked by an Englishman if he did not feel cold without clothes. The skin of the body, always accustomed to cold, can contract whenever the temperature is cold enough to provide
Medsical any risk of cxcessive loss of heat from the system. This contractile power of the skin is regulated by the nervous system. There is a heat centre in the brain which sends messages by means of the nerves to the skin and bloodvessels, making them contract in a cold and dilate in a warm atmosphere. In acute illness, the nervous system is paralysed by the poisons circulating in the blood. The heat centre loses its power of regulating the temperature, and therefore the temperature of the body goes' up, and the patient is in a state of fever. Thus, the home nurse can understand what an important indication the temperature of the patient is as to his bodily condition. From this article, also, she will have gathered that it is essential to keep the skin clean in health and disease by means of daily ablutions. She will know that, because poisons can enter the body through the skin, every care must be taken to prevent the entrance of microbes into the system through the broken skin. The protective function of the skin is assisted by the body of fat which lies beneath it. This fat consists of innumerable cells filled with an oily fluid, and it makes an excellent cushion for the surface of the body, to minimise the effect of jars and shocks. Underneath this skin and fat lie the muscles, or " flesh," which are attached from one bone to another, and act as organs of locomotion.