Physiology and Hygiene for Secondary Schools :: CHAPTER XVI

CHAPTER XVI - THE SKIN

Protective coverings are found at all the exposed surfaces of the body. These vary considerably at different places, each being adapted to the conditions under which it serves. The most important ones are the skin, which covers the entire external surface of the body; the mucous membrane, which lines all the cavities that communicate by openings with the external surface; and the serous membrane, which, including the synovial membranes, lines all the closed cavities of the body. In addition to the protection which it affords, the skin is one of the means by which the body is brought into proper relations with its surroundings. It is because of this function that we take up the study of the skin at this time.

The Skin is one of the most complex structures of the body, and serves several distinct purposes. It is estimated to have an area of from 14 to 16 square feet, and to have a thickness which varies from less than one eighth to more than one fourth of an inch. It is thickest on the palms of the hands and the soles of the feet, the places where it is most subject to wear. It is made up of two distinct layers—an outer layer called the epidermis, or cuticle, and an inner layer called the dermis, or cutis vera (Fig. 121).

The Dermis.—This is the thicker and heavier of the two layers, and is made up chiefly of connective tissue. The network of tough fibers which this tissue supplies, [pg 265] forms the essential body of the dermis and gives to it its power of resistance. It is on account of the connective tissue that the skins of animals can be converted into leather by tanning. A variety of structures, including blood and lymph vessels, oil and perspiratory glands, hair follicles, and nerves, are found embedded in the connective tissue (Fig. 122). These aid in different ways in the work of the skin.

Fig. 121

Fig. 121—Section of skin magnified, a, b. Epidermis, b. Pigment layer. c. PapillÆ, d. Dermis. e. Fatty tissue. f, g, h. Sweat gland and duct. i, k. Hair and follicle. l. Oil gland.

On the outer surface of the dermis are numerous [pg 266]elevations, called papillÆ. These average about one one-hundredth of an inch in height, and one two hundred and fiftieth of an inch in diameter. They are most numerous on the palms of the hands, the soles of the feet, and the under surfaces of the fingers and toes. At these places they are larger than in other parts of the body, and are closely grouped, forming the parallel curved ridges which cover the surfaces. Each papilla contains a loop of capillaries and a small nerve, and many of them are crowned with touch corpuscles (page 342).

Fig. 122

Fig. 122—Diagram of section of skin showing its different structures.

The Epidermis is much thinner than the dermis. It is made up of several layers of cells which are flat and scale-like at the surface, but are rounded in form where the epidermis joins the dermis. The epidermis has the appearance of being moulded onto the dermis, filling up the depressions between the papillÆ and having corresponding irregularities (Fig. 121). No blood vessels are found in the epidermis, its nourishment being derived from the lymph which reaches it from the dermis. Only the part next to the dermis is made up of living cells. These are active, however, in the formation of new cells, which take the place of those that are worn off at the surface. Some of the cells belonging to the inner layer of epidermis contain pigment granules, which give the skin its color (Fig.[pg 267] 121). The epidermis contains no nerves and is therefore non-sensitive. The hair and the nails are important modifications of the epidermis.

A Hair is a slender cylinder, formed by the union of epidermal cells, which grows from a kind of pit in the dermis, called the hair follicle. The oval and somewhat enlarged part of the hair within the follicle is called the root, or bulb, and the uniform cylinder beyond the follicle is called the shaft. Connected with the sides of the follicles are the oil, or sebaceous, glands (Figs. 121 and 122). These secrete an oily liquid which keeps the hair and cuticle soft and pliable. Attached to the inner ends of the follicles are small, involuntary muscles whose contractions cause the roughened condition of the skin that occurs on exposure to cold.

A Nail is a tough and rather horny plate of epidermal tissue which grows from a depression in the dermis, called the matrix. The back part of the nail is known as the root, the middle convex portion as the body, and the front margin as the free edge (Fig. 123). Material for the growth of the nail is derived from the matrix, which is lined with active epidermal cells and is richly supplied with blood vessels. Cells added to the root cause the nail to grow in length (forward) and cells added to the under surface cause it to grow in thickness. The cuticle adheres to the nail around its entire circumference so that the covering over the dermis is complete.

Fig. 123

Fig. 123—Section of end of finger showing nail in position.

Functions of the Skin.—The chief function of the skin is that of protection. It is able to protect the body on account of the tough connective tissue in the dermis, the non-sensitive cells of the epidermis, and also by the touch[pg 268] corpuscles and their connecting nerve fibers. This protection is of at least three kinds, as follows:

1. From mechanical injuries such as might result from contact with hard, rough, or sharp objects. The main quality needed for resisting mechanical injuries is toughness, and this is supplied both by the epidermis and by the connective tissue of the dermis.

2. From chemical injuries caused by contact with various chemical agents, as acids, alkalies, and the oxygen of the air. The epidermis, being of such a nature as to resist to a considerable extent the action of chemical agents, affords protection from these substances. 89

3. From disease germs which are everywhere present. The epidermis is the main protective agent against attacks of germs, but should the epidermis be broken, they meet with further resistance from the fluids of the dermis and the white corpuscles of the blood.

4. From an excessive evaporation of liquid from the surface of the body. In the performance of this function, the skin is an important means of keeping the tissues soft and the blood and lymph from becoming too concentrated.

Other Functions of the Skin.—Through the perspiratory glands the skin is an organ of excretion. While the secretion from a single gland is small, the waste that leaves the body through all of the perspiratory glands is considerable 90 (page 206). By means of the nerves terminating in the touch corpuscles, the skin serves as the organ of touch, or feeling (Chapter XX). To a slight extent also the skin[pg 269] may absorb liquid substances, these being taken up by the blood and lymph vessels, and perform a respiratory function, throwing off carbon dioxide. But the most important function of the skin, in addition to protection, is that of serving as

An Organ of Adaptation.—Forming, as it does, the boundary between the body and its physical environment, the skin is perhaps the most important agent through which the body is adapted to its immediate surroundings. Evidence of this is found in the great variety of influences which are able to affect the body through their action upon the nerves in the skin, and in the changes which the epidermis undergoes on exposure. The latter function is especially marked in the lower animals, the coverings of epidermal tissue (hair, scales, feathers, etc.) adapting each species to the physical conditions under which it lives. In man the most striking example of adaptation through the skin is seen in the variations in the quantity of blood circulating through it, corresponding to the changes in the temperature outside of the body. These variations are of great importance, having to do with the

Maintenance of the Normal Temperature.—It is necessary to the continuance of life that the temperature of the body be kept at a nearly uniform degree, called the normal temperature, which is about 98.6° F. The maintenance of the normal temperature depends mainly upon four conditions: the chemical changes at the cells, the circulation of the blood, the nervous system, and the skin. The chemical changes produce the heat, the blood in its circulation distributes the heat over the body, and the nervous system controls the heat-producing and distributing processes (page 320). The skin is the chief means by which the body[pg 270] gets rid of an excess of heat and, by so doing, avoids overheating. 91

How the Skin cools the Body.—The skin is a means of ridding the body of an excess of heat in at least two ways:

1. By the conduction and radiation of heat from its surface as from a stove. This goes on all the time, but varies with the amount of heat brought to the surface by the blood.

2. By the evaporation of the perspiration. It is a well-established and easily demonstrated principle that liquids in evaporating use up heat.(See Practical Work.) It is also a matter of everyday experience that the perspiration has a cooling effect upon the body and that its flow increases with the amount of heat to be gotten rid of. The quantity of perspiration secreted, and of heat disposed of through its evaporation, also varies with the amount of blood circulating through the skin.

Temperature Regulation by the Skin.—Variations in the quantity of blood circulating through the skin enable this organ to throw off just the right amount of heat for keeping the body at the normal temperature. If it is necessary for the body to rid itself of an excess of heat, the quantity of blood circulating in the skin is increased. This brings the blood near the surface, where more heat can be radiated and where it may cause an increase in the perspiration. On the other hand, if the body is in danger of losing too much heat, the circulation diminishes in the skin and increases in the internal organs. This stops the rapid loss of heat from the surface. The skin in this work[pg 271] is of course made to cooperate with other parts of the body. That it is not the only organ concerned in regulating the escape of heat is seen in the results that follow sensations either of chilliness or of heat at the surface.

Effects of Heat and Cold Sensations.—Sensations, or feelings, of heat and cold are made possible through the nerves which connect the brain with the temperature corpuscles, found in the skin (page 343). As the warm blood recedes from the skin, a sensation of cold is felt, but when the blood returns, there is again the feeling of warmth. The sensation of cold prompts one to seek a warmer place, or to put on more clothing; while the sensation of heat, if it be oppressive, leads to activities of an opposite kind. Prompted in this way by the sensations from the skin, one voluntarily supplies the external conditions, such as clothing and heat, that affect the body temperature.

Alcohol and the Regulation of Temperature.—Alcohol, through its effect upon the nervous system, interferes seriously with the regulation of the body temperature. By dilating the capillaries, it increases the circulation in the skin and leads to an undue loss of heat. At the same time the excess of blood in the skin causes a feeling of warmth which has led to the erroneous belief that alcohol is a heat producer. If taken on a cold day, it deceives one about his true condition and leads to a wasting of heat when it should be carefully economized. Not only is alcohol of no value in maintaining the body temperature, but if taken during severe exposure to cold, it becomes a menace to life itself. Arctic, explorers and others exposed to severe cold have found that they withstand cold far better when no alcohol at all is used.92

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HYGIENE OF THE SKIN

Much of the hygiene of the skin is included in the problems of keeping it warm and clean. It is kept warm by clothing; bathing is the method of keeping it clean.

Clothing should be warm and loose-fitting. Woolen fabrics are to be preferred in winter to cotton because, being poorer conductors of heat, they afford better protection from the cold. But wool fails to absorb the perspiration rapidly from the skin and to pass it to the outside where it is evaporated. This, together with its tendency to irritate, makes woolen clothing somewhat objectionable for wearing next to the skin. This objection, however, is obviated by woolen underwear which is lined by a thin weaving of cotton.

Bathing.—The solid material from the perspiration, which is left on the skin, together with the oil from the oil glands and the dirt from the outside, tends to close up the pores and develop offensive odors. Keeping the skin clean is, for these reasons, necessary from both a health and a social standpoint. While one should always keep clean, the frequency of the bath will depend upon the season, the occupation of the individual, and the nature and amount of the perspiration. As to the kind of bath to be taken and the precautions to be observed, no specific rules can be laid down. These must be determined by[pg 273] the facilities at hand and by the health and natural vigor of the bather. Severe chilling of the body should be avoided, especially by those in delicate health. If a hot bath is taken, one should dash cold water over the body on finishing. One should then quickly dry and rub the body with a coarse towel. The dash of cold water closes the pores of the skin and lessens the liability of taking cold.

The Tonic Bath.—The cold bath has been found to have a beneficial effect upon the general health beyond its effect upon the skin. When taken with care as to the length of time and the degree of cold, decided tonic effects are observed on the circulation and on the nervous system. The rapid changes of temperature vigorously exercise the non-striated muscles of the blood vessels (page 57) and the nerves controlling them. The irritability of the nervous system in general is also lessened. For this reason the cold bath is one of the best means of keeping both mind and body in good condition during the warm months. Sponging off the body with cold or tepid water before retiring is also an excellent aid in securing sound sleep during the hot summer nights.

Danger from the cold bath arises through the shock to the nervous system and the loss of heat from the body. It is avoided by using water whose temperature is not too low and by limiting the time spent in the bath. A brisk rubbing with a coarse towel should always follow the cold bath. People past middle age are, as a rule, not benefited by the cold bath; and those in delicate health, especially if inclined toward rheumatism, are likely to be affected injuriously by it.

Care of the Complexion.—A good complexion is a natural accompaniment of good health and depends primarily[pg 274] upon two conditions—a clear skin and an active circulation of the blood through it. Clearness of the skin depends largely upon the elimination of waste material from the body, and where the solid wastes are not effectively removed through the natural channels (the liver, kidneys, and bowels), blotches, sallowness of the skin, and skin eruptions are likely to result. In seeking to clear the complexion, attention must be given to all those agencies that favor the elimination of waste, and especially should there be a free and thorough evacuation of the bowels each day. The general health should also be looked after, attention being given to exercise, fresh air, proper food,93 sufficient sleep, etc.

Bathing is the chief means employed for increasing the circulation in the skin, although exercise which is sufficiently vigorous to cause one to perspire freely is a valuable aid. A daily bath of warm or hot water, finished off with a dash of cold, followed by a thorough rubbing of the entire surface, and this by a kneading of the skin with the thumbs and fingers, will in most cases bring about the desired results. A little olive oil, thoroughly worked into the skin during the kneading process, is beneficial where one lacks flesh or where the skin is dry and thin. The olive oil is also beneficial where the baths are exhausting or render one susceptible to cold. In rubbing and kneading, the skin should not be bruised or irritated.

The much advertised "complexion beautifiers" which are applied directly to the face frequently have the effect of clogging the pores and of causing eruptions of the skin. [pg 275]On the other hand, certain authorities state that the cold cream preparations may be of advantage in giving the skin a desired softness, and that when judiciously used (the face being cleansed after each application) they do no harm. Of the different kinds of face powder those prepared from rice are considered the least injurious.

Treatment of Skin Wounds.—Skin wounds which may not be serious in themselves frequently become so through getting infected with germs. Blood poisoning often results from such infections, one of the worst forms being tetanus, or lockjaw. A wound should be kept clean, and if it shows signs of infection, it should be washed with some antiseptic solution. Or, it may be cleansed with pure warm water and then covered with some antiseptic ointment,94 of which there are a number on the market. A weak solution of carbolic acid (one part acid to twenty-five parts of water) makes an excellent antiseptic wash. It may be used not only for cleansing wounds, but also in counteracting the poisonous effects that follow the bites of insects.

A wound resulting from the bite of an animal (cat or dog), even though slight, should receive more serious attention, and as soon as possible after the occurrence. Such wounds should be cauterized, and for this purpose pure carbolic, acid (undiluted with water) may be used. A wooden toothpick is dipped into the acid and this is worked about in the wound. The acid is then washed out with warm water. A deep wound from a rusty nail or[pg 276] a thorn should be treated in the same manner and should be kept open, not being allowed to heal at the surface first. If one has reason to believe he has been bitten by a mad dog, the wound should be cauterized as above, and a physician should be summoned at once. Deep wounds from explosives, or other causes, should also receive the attention of the physician. Many cases of lockjaw result every year from wounds inflicted by the toy pistols, firecrackers, etc., used in our Fourth of July celebrations. These are due to the embedding in the skin or flesh of small solid particles on which are lockjaw germs. Wounds of this nature should, of course, receive the attention of the physician.

Care of the Nails.—Relief from a blood blister under the nail is secured by boring a small hole through the nail with the sharp point of a sterilized penknife (page 38). This simple bit of surgery not only relieves the pain, but is frequently the only means of saving the nail. Ingrown toe nails are relieved by scraping a broad strip in the middle of the nail until very thin. This relieves the pressure, preventing the sides of the nail from being forced into the toe. While the finger nails should be trimmed in a curve, corresponding to the end of the finger, it is recommended that the toe nails be cut straight across (Fig. 124), as this method diminishes the pressure from the shoe and keeps the nails from ingrowing. Shoes that pinch the toes should, of course, not be worn (page 238).

Fig. 124

Fig. 124—Proper method of trimming nails of toes.

Care of the Hair.—Occasional washing of the hair is beneficial, but too much wetting causes decay of the hair roots, which leads to its falling out. The worst enemy of the hair is dandruff. A method of removing dandruff which is highly recommended is that of rubbing olive oil[pg 277] into the scalp and later of removing this with a cleansing shampoo. The olive oil is placed on the scalp with a medicine dropper and thoroughly rubbed in with the fingers. After three or four hours the hair is washed with soap and water (any good toilet soap will do) and rinsed with pure water. The hair is then dried, the surplus water being removed with a coarse towel. Where the dandruff is very troublesome, this treatment may be given once or twice a week; but in mild cases once a month is sufficient. Massage of the scalp, by increasing the circulation at the hair roots, is beneficial, but irritation by a fine-tooth comb, a stiff hair brush, or by other means should be avoided. Frequent brushing and combing, however, are necessary both for the good appearance of the hair and for spreading the oil secreted by the glands at the hair roots.

Summary.—The skin forms the external covering of the body and also serves additional purposes. It is a most important agency in adapting the body to its physical surroundings, as shown by the part which it plays in the regulation of the body temperature. The skin should be kept clean and active, and skin wounds, even though small, should be guarded against infection.

Exercises.—1. Name an example of each of the protective coverings of the body.

2. Compare the dermis and the epidermis with reference to thickness, composition, and function.

3. To what is the color of the skin due? How is the color of the skin affected by the sunlight?

4. What modifications of the epidermis are found on our bodies? What are found on the body of a chicken?

5. What different kinds of protection are provided by the skin?

6. How does the perspiration cool the body?

7. What change occurs in the circulation in the skin when the body is becoming too cold? When becoming too warm? What is the purpose of these changes?

[pg 278]8. How does alcohol cause one to feel warm when he may be losing too much of his heat?

9. What precaution should be observed by one in poor health, in taking a bath?

10. How may the cold bath be a means of improving the general health?

PRACTICAL WORK

Observations on the Skin and its Appendages.—Examine the palm of the hand with a lens. Note the small ridges which correspond to the rows of papillÆ beneath the cuticle. In these find small pits, which are the openings of the sweat glands.

2. Examine the epidermis on the back of the hand and palm. At which place is it thickest and most resisting? Is it of uniform thickness over the palm? Try picking it with a pin at the thickest place, noting if pain is felt. Inference?

3. Examine a finger nail. Is the free edge or the root the thickest? Trim closely the thumb nail and the nail of the middle finger of one hand and try to pick up a pin, or other minute object, from a smooth, hard surface. The result indicates what use of the nails? Suggest other uses.

4. Examine with a microscope under a low power hairs from a variety of animals, as the horse, dog, cat, etc., noting peculiarities of form and surface.

To illustrate Cooling Effects of Evaporation.—1. Wet the back of the hand and move it through the air to hasten evaporation. Observe that, as the hand dries, a sensation of cold is felt. Repeat the experiment, using ether, alcohol, or gasolene instead of the water, noting the differences in results. These liquids evaporate faster than water.

2. Wet the bulb of a thermometer with alcohol or water. Move it through the air to hasten evaporation. Note and account for the fall of the mercury.

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