Part 11

THE NAILS protect the ends of the tender finger, and toe, and give us power more firmly to grasp and easily to pick up any object we may desire. They enable us to perform a hundred little, mechanical acts which else were impossible. At the same time, their delicate color and beautiful outline give a finish of ornament to that exquisite instrument, the hand. The nail is firmly set in a groove (matrix) in the cuticle, from which it grows at the root in length [Footnote: By making a little mark on the nail near the root we can see, week by week, how rapidly this process goes on, and so form some idea of what a multitude of cells must be transformed into the horny matter of the nail.] and from beneath in thickness. So long as the matrix at the root is uninjured, the nail will be replaced after any accident. (See p. 288.)

III. THE MUCOUS MEMBRANE.

STRUCTURE.--At the edges of the openings into the body, the skin seems to stop and give place to a tissue which is redder, more sensitive, more liable to bleed, and is moistened by a fluid, or mucus, as it is called. Really, however, the skin does not cease, but passes into a more delicate covering of the same general structure, viz., an outer, hard, bloodless, insensible layer, and an inner, soft, sanguine, nervous one. [Footnote: With a dull knife, we can scrape from the mucous membrane which lines the mouth some of the cuticle for examination under the microscope. In a similar way, we can obtain cuticle from the surface of the body for study and comparison.] Thus every part of the body is wrapped in a kind of double bag, made of tough skin on the outside, and tender mucous membrane on the inside.

CONNECTIVE TISSUE.--The cutis and the corresponding layer of the mucous membrane consist chiefly of a fibrous substance interlaced, like felt. It is called connective tissue, because it connects all the different parts of the body. It spreads from the cutis, invests muscles, bones, and cartilages, and thence passes into the mucous membrane. So thoroughly does it permeate the body, that, if the other tissues were destroyed, it would give a perfect model of every organ. [Footnote: It is curious to notice how our body is wrapped in membrane. On the outside, is the skin protecting from exterior injury, and, on the inside, is the mucous membrane reaching from the lips to the innermost air cell of the lungs. Every organ is enveloped in its membrane. Every bone has its sheath. Every socket is lined. Even the separate fibers of muscles have their covering tissue. The brain and the spinal cord are triply wrapped, while the eye is only a membranous globe filled with fluid. These membranes protect and support the organs they enfold, but, with that wise economy so characteristic of nature everywhere, they have also an important function to perform. They are the filters of the body. Through their pores pass alike the elements of growth, and the returning products of waste. On one side, bathed by the blood, they choose from it suitable food for the organ they envelop, and many of them in their tiny cells, by some mysterious process, form new products,--put the finishing touches, as it were, upon the material ere it is deposited in the body.] It can be seen in a piece of meat as a delicate substance lying between the layers of muscle, where it serves to bind together the numerous fibers of which they are composed.

Connective tissue yields gelatine on boiling, and is the part which tans when hides are manufactured into leather. It is very elastic, so that when you remove your finger after pressing upon the skin, no indentation is left. [Footnote: In dropsy, this elasticity is lost by distension, and there is a kind of "pitting," as it is called, produced by pressure.] It varies greatly in character,--from the mucous membrane, where it is soft and tender, to the ligaments and tendons which it largely composes, where it is strong and dense. [Footnote: The leather made from this tissue varies as greatly, from the tough, thick oxhide, to the soft, pliable kid and chamois skin.]

FAT is deposited as an oil in the cells [Footnote: So tiny are these cells, that there are over sixty-five million in a cubic inch of fat. As they are kept moist, the liquid does not ooze out, but, on drying, it comes to the surface, and thus a piece of fat feels oily when exposed to the air. The quantity of fat varies with the state of nutrition. In corpulent persons, the masses of fat beneath the skin, in the mesentery, on the surface of the heart and great vessels, between the muscles, and in the neighborhood of the nerves, are considerably increased. Conversely, in the emaciated we sometimes find beneath the skin nucleated cells, which contain only one oil drop. Many masses of fat which have an important relation to muscular actions--such as the fat of the orbit or the cheek-- do not disappear in the most emaciated object. Even in starvation, the fatty substances of the brain and spinal cord are retained.--VALENTIN.] of this tissue, just beneath the skin (Fig. 24), giving roundness and plumpness to the body, and acting as an excellent nonconductor for the retention of heat. It collects as pads in the hollows of the bones, around the joints, and between the muscles, causing them to glide more easily upon each other. As marrow, it nourishes the skeleton, and also distributes the shock of any jar the limb may sustain.

It is noticeable, however, that fat does not gather within the cranium, the lungs, or the eyelids, where its accumulation would clog the organs.

IV. THE TEETH.

THE TEETH [Footnote: Although the teeth are always found in connection with the skeleton, and are, therefore, figured as a part of it (Fig. 1), yet they do not properly belong to the bones of the body, and are merely set in the solid jaw to insure solidity. They are hard, and resemble bony matter, yet they are neither true bone nor are they formed in the same manner. "They are properly appendages of the mucous membrane, and are developed from it."--LEIDY. "They belong to the Tegumentary System, which, speaking generally of animals, includes teeth, nails, horns, scales, and hairs."--MARSHALL. They are therefore classed with the mucous membrane, as are the nails and hair with the skin.] are thirty-two in all,--there being eight in each half jaw, similarly shaped and arranged. In each set of eight, the two nearest the middle of the jaw have wide, sharp, chisel-like edges, fit for cutting, and hence are called incisors. The next one corresponds to the great tearing or holding tooth of the dog, and is styled the canine, or eye-tooth. The next two have broader crowns, with two points, or cusps, and are hence termed the bicuspids. The remaining three are much broader, and, as they are used to crush the food, are called the grinders, or molars. The incisors and eyeteeth have one fang, or root; the others have two or three fangs.

THE MILK TEETH.--We are provided with two sets of teeth. The first, or milk teeth, are small and only twenty in number. In each half jaw there are two incisors, one canine, and two molars. The middle incisors are usually cut about the age of seven months, the others at nine months, the first molars at twelve months, the canines at eighteen months, and the remaining molars at two or three years of age. The lower teeth precede the corresponding upper ones. The time often varies, but the order seldom.

THE PERMANENT TEETH.--At six years, when the first set is usually still perfect, the jaws contain the crowns of all the second, except the wisdom teeth. About this age, to meet the wants of the growing body, the crowns of the permanent set begin to press against the roots of the milk teeth, which, becoming absorbed, leave the loosened teeth to drop out, while the new ones rise and occupy their places. [Footnote: If the milk teeth, do not promptly loosen on the appearance of the second set, the former should be at once removed to permit the permanent teeth to assume their natural places. If any fail to come in regularly, or if they crowd the others, a competent dentist should be consulted.]

FIG. 25.

The central incisors appear at about seven years of age; the others at eight; the first bicuspids at nine, the second at ten; the canines at eleven or twelve; the second [Footnote: The first molar appears much earlier. (See Fig. 25.)] molars at twelve or thirteen, and the last, or wisdom teeth, are sometimes delayed until the twenty-second year, or even later.

STRUCTURE OF THE TEETH.--The interior of the tooth consists principally of dentine, a dense substance resembling bone. [Footnote: In the tusk of the elephant this is known as ivory.] The crown of the tooth, which is exposed to wear, is protected by a sheath of enamel. This is a hard, glistening, white substance, containing only two and a half per cent of animal matter. The fang is covered by a thin layer of true bone (cement).

FIG. 26.

At the center of the tooth is a cavity filled with a soft, reddish-white, pulpy substance full of blood vessels and nerves. This pulp is very sensitive, and toothache is caused by its irritation.

THE FITTING OF THE TOOTH INTO THE JAW is a most admirable contrivance. It is not set like a nail in wood, having the fang in contact with the bone; but the socket is lined with a membrane which forms a soft cushion. While this is in a healthy state, it deadens the force of any shock, but, when inflamed, it becomes the seat of excruciating pain.

THE DECAY OF THE TEETH [Footnote: Unlike the other portions of the body, there is no provision made for any change in the permanent teeth. That part, however, which is thus during life most liable to change, after death resists it the longest. In deep-sea dredgings teeth are found when all traces of the frame to which they belonged have disappeared. Yet hard and incorruptible as they seem, their permanence is only relative. Exposed to injury and disease, they break or decay. Even if they escape accident, they yet wear at the crown, are absorbed at the fang, and, in time, drop out, thus affording another of the many signs of the limitations Providence has fixed to the endurance of our bodies and the length of our lives.] is commonly caused (1) by portions of the food which become entangled between them, and, on account of the heat and moisture, quickly decompose; and (2) by the saliva, as it evaporates, leaving on the teeth a sediment, which we call tartar. This collects organic matter that rapidly changes, and also affords a soil in which a sort of fungus speedily springs up. From both these causes, the breath becomes offensive, and the teeth are injured.

PRESERVATION OF THE TEETH.--Children should early be taught to brush their teeth at least every morning with tepid water, and twice a week with white castile soap and powdered orris root, or with some dentifrice recommended by a responsible dentist. They should also be instructed to remove the particles of food from between the teeth, after each meal, by means of a quill or wooden toothpick.

The enamel once injured is never restored, and the whole interior of the tooth is exposed to decay. We should not, therefore, crack hard nuts, bite thread, or use metal toothpicks, gritty tooth powders, or any acid which "sets the teeth on edge," i. e.. that acts upon the enamel. It is well also to have the teeth examined yearly by a dentist, that any small orifice may be filled, and further decay prevented.

V. THE GLANDS OF THE SKIN.

1. THE OIL GLANDS are clusters of tiny sacs which secrete an oil that flows along the duct to the root of the hair, and thence oozes out on the cuticle (Fig. 24). [Footnote: This secretion is said to vary in different persons, and on that account the dog is enabled to trace his master by the scent.] This is nature's efficient hair-dressing, and also keeps the skin soft and flexible. These glands are not usually found where there is no hair, as on the palm of the hand, and hence at those points only can water readily soak through the skin into the body. They are of considerable size on the face, especially about the nose. When obstructed, their contents become hard and dark-colored, and are vulgarly called "worms." [Footnote: Though they are not alive, yet, under the microscope, they are sometimes found to contain a curious parasite, called the pimple mite, which is supposed to consume the superabundant secretion.]

II. THE PERSPIRATORY GLANDS are fine tubes about 1/300 of an inch in diameter, and a quarter of an inch in length, which run through the cutis, and then coil up in little balls (Fig. 24). They are found in all parts of the body, and in almost incredible numbers. In the palm of the hand, there are about two thousand eight hundred in a single square inch. On the back of the neck and trunk, where they are fewest, there are yet four hundred to the square inch. The total number on the body of an adult is estimated at about two and a half million. If they were laid end to end, they would extend nearly ten miles. [Footnote: The current statement, that they would extend twenty-eight miles, is undoubtedly an exaggeration. Krause estimates the total number at 2,381,248, and the length of each coil, when unraveled, at 1/10 of an inch, which would make the total length much less than even the statement in the text. Seguin states that the proportion of impurities thrown off by the skin and the lungs, is eleven to seven.] The mouths of these glands--"pores," as we commonly call them--may be seen with a pocket lens along the fine ridges which cover the palm of the hand.

THE PERSPIRATION.--From these openings, there constantly passes a vapor, forming what we call the insensible perspiration. Exercise or heat causes it to flow more freely, when it condenses on the surface in drops. The perspiration consists of about ninety-nine parts water, and one part solid matter. The amount varies greatly, but on the average is, for an adult, not far from two pounds per day. Any suppression of this constant drainage will lead to disagreeable and even dangerous results. If it be entirely and permanently checked, death will inevitably ensue. [Footnote: Once, on an occasion of great solemnity at Rome, a child was, it is said, completely covered with gold leaf, closely applied to the skin, so as to represent, according to the idea of that age, the golden glory of an angel or seraph. In a few hours, after contributing to this pageant, the child died; the cause being suffocation, from stopping the exhalation of the skin; although, in the ignorance of the common people of those days, the death was attributed to the anger of the Deity, and looked upon as a circumstance of evil omen.]

THE ABSORBING POWER OF THE SKIN.--We have already described two uses of the skin: (1) Its protective, (2) its exhaling, and now we come to (3) its absorbing power. This is not so noticeable as the others, and yet it can be illustrated. Persons frequently poison their hands with the common wood ivy. Contagious diseases are taken by touching a patient, or even his clothing, especially if there be a crack in the cuticle. [Footnote: If one is called upon to handle a dead body, it is well, especially if the person has died of a contagious disease, to rub the hand with lard or olive oil. Poisonous matter has been fatally absorbed through the breaking of the cuticle by a hangnail, or a simple scratch. There is a story that Bonaparte, when a lieutenant of artillery, in the heat of battle, seized the rammer and worked the gun of an artilleryman who had fallen. From the wood which the soldier had used, Bonaparte absorbed a poison that gave him a skin disease, by which he was annoyed the remainder of his life.] Painters absorb so much lead through the pores of their hands that they are attacked with colic. [Footnote: Cosmetics, hair dyes, etc., are exceedingly injurious, not only because they tend to fill the pores of the skin, but because they often contain poisonous matters that may be absorbed into the system, especially if they are in a solution.] Snuff and lard are frequently rubbed on the chest of a child suffering with the croup, to produce vomiting. It is said that seamen in want of water drench their clothing in salt spray, when the skin will absorb enough moisture to quench thirst (see Lymphatic System).

By carefully conducted experiments, it has been found that the skin acts in the same way as the lungs (see Respiration) in absorbing oxygen from the air, and giving off carbonic acid to a small but appreciable amount. Indeed, the skin has not inaptly been styled the third lung. Hence, the importance of absolute cleanliness and a frequent ablution of the entire body.

VI. HYGIENE.

HINTS ABOUT WASHING AND BATHING.--The moment of rising from bed is the proper time for the full wash or bath with which one should commence the day. The body is then warm, and can endure moderately cold water better than at any other time; it is relaxed, and needs bracing; and the nerves, deadened by the night's repose, require a gentle stimulus. If the system be strong enough to resist the shock, cold water is the most invigorating; if not, a tepid bath will answer. [Footnote: Many persons have not the conveniences for a bath. To them, the following plan, which the author has daily employed for years, is commended. The necessities are: a basin full of soft water, a mild soap, a large sponge or a piece of flannel, and two towels--one soft, the other rough. The temperature of the water should vary with the season of the year--cold in summer and tepid in winter. Rub quickly the entire body with the wet sponge or flannel. (If more agreeable, wash and wipe only a part at a time, protecting the rest in cold weather with portions of clothing.) Dry the skin gently with a soft towel, and when quite dry, with the rough towel or flesh brush rub the body briskly four or five minutes till the skin is all aglow. The chest and abdomen need the principal rubbing. The roughness of the towel should be accommodated to the condition of the skin. Enough friction, however, must be given to produce at least a gentle warmth, indicative of the reaction necessary to prevent subsequent chill or languor. An invalid will find it exceedingly beneficial if a stout, vigorous person produce the reaction by rubbing with the hands.]