LESSON XVI. THE SKIN.-ITS COMPLICATED MECHANISM. 1. THE skin is a very curious piece of mechanism,1 and it performs many wonderful and important offices. The more we study it, the more we shall find in it to surprise us; the more to admire in the wisdom which planned it; and the more fully we shall be convinced that the preservation of health depends as much upon the proper care we take of it, as of the organs within the body. 2. The skin is not merely a thin covering for the body, just to keep it warm, or to protect the parts from injury. It is something more than this. When we examine it we find that it is really very complicated2 in structure, and we begin to wonder what can be the object of so curious a piece of machinery. 3. First, all over the surface of the body, is a very thin and transparent layer, called the cuticle,3 or scarf-skin. It is, at first, a thin fluid that is poured out from the blood-vessels of the skin, and which, spreading over the true skin, becomes hardened into a thin layer. It is constantly forming, and constantly passing away. It has neither nerves nor bloodvessels, and is therefore without feeling. It is like the outer or rough bark of trees. On the under side of the cuticle is a thin colored layer, that gives color to the complexion. 4. Below the cuticle is what is called the true skin; and this is full of, 1st, arteries and veins, or capillary blood-vessels; 2d, nerves; 3d, lymphatic vessels; 4th, oil-tubes; and, 5th, perspiratory tubes. Let us see if we can understand something of the number, arrangement, plan, and uses of these vessels; for we may be assured this complicated mechanism was not made in vain. THE CAPILLARIES OF THE SKIN. 5. The arteries, bringing the blood from the heart, branch out all over the skin in a net-work of minute fibres; and in this net-work, so fine that the eye can not trace all its parts, the veins begin, and, gathering up the blood, carry it back to the heart again. This net Artery Fig. 15. Vein. work connecting the arteries and veins, spread all through the true skin like the smallest imaginable hairs interlacing and crossing each other in every direction, is a part of what is called the capillary system. The drawing here given, showing an artery carrying the blood to the capillaries, and a vein taking it back to the heart, is a magnified view of what, in reality, is not so large as a pin-head. 6. But these capillary blood-vessels are not only spread over the skin, but also over and through every muscle, and bone, and nerve, and to every part of the body that requires nourishment. By the blood coming from the arteries every part is thus nourished; and by the veins the waste particles are carried away to be thrown out of the system. So numerous are these capillary vessels in the skin, that if the skin be punctured by the finest needle, some of them will be broken by it. NERVES OF THE SKIN.-7. All the veins, and arteries, and capillaries, are so covered with a net-work of nerves, that no part of the skin can be punctured without piercing a nerve, and causing pain. But, although the skin is the organ of touch, and every where capable of exciting feeling, yet the nerves, by which we feel, do not come quite to the surface. They are all covered by the outer layer, or cuticle, which we have described. 8. When the cuticle is taken off, the true skin is found to be covered with little erect cones, called pa-pil'-læ, which, however, can scarcely be seen by the naked eye. Each one of these pa-pil'-la penetrates nearly through the cuticle; and each one, although so small that we can scarcely see it, contains a loop of blood-vessels and a twig of a nerve; and these Fig. 16 shows some of the pa-pil'-læ from the palm of the hand, greatly magnified. They are about the one hundredth part of an inch in height; but it would take 250 of them, placed side by side, to make an inch in diameter. The pa-pil'-læ are numerous wherever the sense of touch is very acute- that is, wherever they are most needed, as at the ends of the fingers, and the tip of the tongue. They are numerous in the tip of the snout of the mole, at the end of the elephant's trunk, and at the root of the whiskers, or feelers, of the cat. nerves enable us to feel any thing that we touch. These little pa-pil'-læ, filled with nerves, are like sentinels every where on duty, and they instantly send news to the brain when a part has been injured. In the tender and delicate parts of the system, which require the most care and protection, like the eye and the lungs, they are the most numerous. If a particle of dust lodges on the eyeball, how quickly do the nerves in the pa-pil'-lo send notice to the brain, that it may be removed! (See Fig. 16.) LYMPHATICS.—9. In addition to the capillary blood-vessels and the nerves, the skin contains a system of tubular vessels called lym-phat-ics, or absorbents, which are so small that they can not be seen by the naked eye. The lymphatics open outwardly on the under surface of the cuticle or scarf-skin, while inwardly they open into the veins. Is it possible that these little vessels are of any use? Yes; and it is very certain that they have not been made in vain. 10. There is one thing, at least, which they are able to do. The mouths, or outward openings of the absorbents, are so exposed that substances placed upon the skin are taken up by them, carried along their little tubes, and emptied into the veins, whence they are carried to that great working engine, the heart, and then sent all over the system. It is very evident that if the substances thus absorbed by the lymphatics are good and useful to the system, they may benefit the whole body; but, if they are bad, they may do it a great amount of injury. 11. If the arm should be dipped in poison, what, probably, would be the result? The lymphatics would doubtless absorb the poison, and empty it into the veins, and the veins would carry it to the heart, and the heart would carry it to every part of the body, to every muscle, and bone, and sinew, and nerve, poisoning all; and death might be the result. Such cases have often happened. 12. The writer of this knew a person who, having washed a number of sheep in a decoction of tobacco to kill the vermin on them, was so poisoned by the juice of the tobacco that was taken up by the lymphatics of the hands and arms, and carried into the blood, that he was made sick, and con fined to his bed for three months. In another case, several children in a family were actually killed by putting on their hands and arms a poisonous ointment by mistake. It is by the lymphatics that the poison from the bite of a mad dog, or a serpent, is carried into the system. 13. Physicians sometimes make use of the lymphatics to a very good purpose. In the process of vaccination," by which multitudes of lives are saved annually, a small particle of matter, placed under the outer skin, and being soon absorbed, affects the whole system, and protects it from the ravages of that terrible disease, the small-pox. Sometimes, when the stomach rejects a medicine, physicians give it by binding a quantity on the arm, after first removing the outer skin by a blister. It is also stated that persons have been fed through the skin, and kept alive for a long time by the absorption of nutritious substances.* OIL-TUBES. 14. We have also said that the skin is full of oil-tubes. These draw oil from the blood, and spread it over the outer skin to keep the latter moist. In some parts of the body they are very abundant. Their little openings may be seen along the edges of the eyelids. The oil which they pour out there keeps the tears and moisture of the eyes within the lids, and also prevents that adhesion of the lids which occurs upon slight inflammation. These oil-tubes are also abundant on the head, where they supply the hair with a pomatum of Nature's own preparing. 1 MĚCH'-AN-ISM, machine work; the parts 6 DE-CŎe'-TION, the liquor in which any of a machine. thing has been boiled or steeped. 2 €ŎM'-PLI-¤Ã-TED, intricate; composed of 7 VAC-CIN-A-TION, the act of inoculating, or many parts united. 3 EU'-TI-CLE, the outer or scarf skin. 4 PUNC'-TŪRED, pierced. 5 TU-BU-LAR, having the form of a tube. applying the vaccine matter to the skin. 8 AD-HE'-SION, sticking together. 9 PO-MA'-TUM, a perfumed ointment. * "A person who has abstained from water will, after he has immersed his body in a bath, not only find his weight increased, but the sensation of thirst abated."-DRAPER. LESSON XVII. GROWTH AND DECAY-LIFE AND DEATH. 1. The most curious part of the skin is the numerous and minute PERSPIRATION-TUBES which it contains. These tubes open on the cuticle, and the openings are called pores of the skin. They descend into the true skin, where they form a coil, as seen in the drawing below. Small as are these tubes, they are lined on their inner surface with branches of the minute capillary blood-vessels, which we have described, and which are filled with the impure venous blood that is on its way back to the heart and lungs. 2. But what can be the object of all this complicated arrangement? Why are these little perspiration-tubes, as they are called, scattered thick all over the body-so thick, indeed, that thirty-five hundred of their little mouths have been counted on one square inch of the hand? What office have they to perform that is not performed by the capillaries, or the nerves, or the lymphatics, or the oil-tubes? Does there seem to be any necessity for them? Let us see. Fig. 17 is a representation of one of the perspiration-tubes, or su-dor-ip'-arous glands, from the palm of the hand. The space from d to b represents a greatly magnified view of the thickness of the skin. The upper portion is the cuticle, the dark portion the colored layer, and the lower portion the true skin. The coil at the bottom, a, a, is imbedded in the surrounding fat, c, c. The tube opens on the surface of the skin, in a slight depression of the cuticle, at d. Fig. 18 is a greatly mag nified view of the surface Fig. 17. |