A, membrane of the hair-follicle, cells with nuclei and pigmentary granules; B, external lining of the root sheath; C, internal lining of the root sheath; D, cortical or fibrous portion of the hair shaft; E, medullary portion (pith) of shaft; F, hair-bulb, showing its development from cells from A.

The golden rule of all bathing is that it must never be followed by a chill. If even a chilliness occur after bathing, it must immediately be broken up by some appropriate methods, as lively exercise, brisk friction, hot drinks, and the application of heat.

Swimming is a most valuable accomplishment, combining bathing and exercise. Bathing of the feet should never be neglected. Cleanliness of the hair is also another matter requiring strict attention, especially in children.

248. Care of the Hair and Nails. The hair brush should not be too stiff, as this increases the tendency towards scurfiness of the head. If, however, the hair is brushed too long or too hard, the scalp is greatly stimulated, and an increased production of scurf may result. If the head be washed too often with soap its natural secretion is checked, and the scalp becomes dry and scaly. The various hair pomades are as a rule undesirable and unnecessary.

The nails should be kept in proper condition, else they are not only unsightly, but may serve as carriers of germs of disease. The nails are often injured by too much interference, and should never be trimmed to the quick. The upper surfaces should on no account be sc.r.a.ped. The nail-brush is sufficient to cleanse them without impairing their smooth and polished surfaces.

[Ill.u.s.tration: Fig. 107.--Longitudinal Section of a Finger-Nail.

A, last phalanx of the fingers; B, true skin on the dorsal surface of the finger; C, epidermis; D, true skin; E, bed of the nail; F, superficial layer of the nail; H, true skin of the pulp of the finger.

249. Use of Clothing. The chief use of clothing, from a hygienic point of view, is to a.s.sist in keeping the body at a uniform temperature.

It also serves for protection against injury, and for personal adornment.

The heat of the body, as we have learned, is normally about 98 1/2 F.

This varies but slightly in health. A rise of temperature of more than one degree is a symptom of disturbance. The normal temperature does not vary with the season. In summer it is kept down by the perspiration and its rapid evaporation. In winter it is maintained by more active oxidation, by extra clothing, and by artificial heat.

The whole matter of clothing is modified to a great extent by climatic conditions and local environments,--topics which do not come within the scope of this book.

250. Material Used for Clothing. It is evident that if clothing is to do double duty in preventing the loss of heat by radiation, and in protecting us from the hot rays of the sun, some material must be used that will allow the pa.s.sage of heat in either direction. The ideal clothing should be both a bad conductor and a radiator of heat. At the same time it must not interfere with the free evaporation of the perspiration, otherwise chills may result from the acc.u.mulation of moisture on the surface of the body.

Wool is a bad conductor, and should be worn next the skin, both in summer and winter, especially in variable climates. It prevents, better than any other material, the loss of heat from the body, and allows free ventilation and evaporation. Its fibers are so lightly woven that they make innumerable meshes enclosing air, which is one of the best of non-conductors.

Silk ranks next to wool in warmth and porosity. It is much softer and less irritating than flannel or merino, and is very useful for summer wear. The practical objection to its general use is the expense. Fur ranks with wool as a bad conductor of heat. It does not, however, like wool, allow of free evaporation. Its use in cold countries is universal, but in milder climates it is not much worn.

Cotton and linen are good conductors of heat, but are not absorbents of moisture, and should not be worn next the skin. They are, however, very durable and easily cleansed. As an intermediate clothing they may be worn at all seasons, especially over wool or silk. Waterproof clothing is also useful as a protection, but should not be worn a longer time than necessary, as it shuts in the perspiration, and causes a sense of great heat and discomfort.

The color of clothing is of some importance, especially if exposed directly to the sun's rays. The best reflectors, such as white and light gray clothing, absorb comparatively little heat and are the coolest, while black or dark-colored materials, being poor reflectors and good absorbents, become very warm.

251. Suggestions for the Use of Clothing. Prudence and good sense should guide us in the spring, in changing winter flannels or clothing for fabrics of lighter weight. With the fickle climate in most sections of this country, there are great risks of severe colds, pneumonia, and other pulmonary diseases from carelessness or neglect in this matter. A change from heavy to lighter clothing should be made first in the outer garments, the underclothing being changed very cautiously.

The two essentials of healthful clothing are cleanliness and dryness. To wear garments that are daily being soiled by perspiration and other cutaneous excretions, is a most uncleanly and unhealthful practice. Clothing, especially woolen underclothing, should be frequently changed. One of the objections to the use of this clothing is that it does not show soiling to the same extent as do cotton and linen.

Infectious and contagious diseases may be conveyed by the clothing. Hence, special care must be taken that all clothing in contact with sick people is burned or properly disinfected. Children especially are susceptible to scarlet fever, diphtheria, and measles, and the greatest care must be exercised to prevent their exposure to infection through the clothing.

We should never sleep in a damp bed, or between damp sheets. The vital powers are enfeebled during sleep, and there is always risk of pneumonia or rheumatism. The practice of sitting with wet feet and damp clothing is highly injurious to health. The surface of the body thus chilled may be small, yet there is a grave risk of serious, if not of fatal, disease. No harm may be done, even with clothing wet with water or damp with perspiration, so long as exercise is maintained, but the failure or inability to change into dry garments as soon as the body is at rest is fraught with danger.

Woolen comforters, scarfs, and fur m.u.f.flers, so commonly worn around the neck, are more likely to produce throat troubles and local chill than to have any useful effect. Harm ensues from the fact that the extra covering induces local perspiration, which enfeebles the natural defensive power of the parts; and when the warmer covering is removed, the perspiring surface is readily chilled. Those who never bundle their throats are least liable to suffer from throat ailments.

252. Ill Effects of Wearing Tightly Fitting Clothing. The injury to health caused by tight lacing, when carried to an extreme, is due to the compression and displacement of various organs by the pressure exerted on them. Thus the lungs and the heart may be compressed, causing short breath on exertion, palpitation of the heart, and other painful and dangerous symptoms. The stomach, the liver, and other abdominal organs are often displaced, causing dyspepsia and all its attendant evils. The improper use of corsets, especially by young women, is injurious, as they interfere with the proper development of the chest and abdominal organs. The use of tight elastics below the knee is often injurious. They obstruct the local venous circulation and are a fruitful source of cold feet and of enlarged or varicose veins.

Tightly fitting boots and shoes often cause corns, bunions, and ingrowing nails; on the other hand, if too loosely worn, they cause corns from friction. Boots too narrow in front crowd the toes together, make them overlap, and render walking difficult and painful. High-heeled boots throw the weight of the body forwards, so that the body rests too much on the toes instead of on the heels, as it should, thus placing an undue strain upon certain groups of muscles of the leg, in order to maintain the balance, while other groups are not sufficiently exercised. Locomotion is never easy and graceful, and a firm, even tread cannot be expected.

The compression of the scalp by a tight-fitting hat interferes with the local circulation, and may cause headaches, neuralgia, or baldness, the nutrition of the hair-follicles being diminished by the impaired circulation. The compression of the chest and abdomen by a tight belt and various binders interferes with the action of the diaphragm,--the most important muscle of respiration.

253. Miscellaneous Hints on the Use of Clothing. Children and old people are less able to resist the extreme changes of temperature than are adults of an average age. Special care should be taken to provide children with woolen underclothing, and to keep them warm and in well-ventilated rooms. Neither the chest nor limbs of young children should be unduly exposed, as is often done, to the cold blasts of winter or the fickle weather of early spring. Very young children should not be taken out in extremely cold weather, unless quite warmly clad and able to run about.

The absurd notion is often entertained that children should be hardened by exposure to the cold. Judicious "hardening" means ample exposure of well-fed and well-clothed children. Exposure of children not thus cared for is simple cruelty. The many sicknesses of children, especially diseases of the throat and lungs, may often be traced directly to gross carelessness, ignorance, or neglect with reference to undue exposure. The delicate feet of children should not be injured by wearing ill-fitting or clumsy boots or shoes. Many deformities of the feet, which cause much vexation and trouble in after years, are acquired in early life.

No one should sleep in any of the clothes worn during the day, not even in the same underclothing. All bed clothing should be properly aired, by free exposure to the light and air every morning. Never wear wet or damp clothing one moment longer than necessary. After it is removed rub the body thoroughly, put on at once dry, warm clothing, and then exercise vigorously for a few minutes, until a genial glow is felt. Neglect of these precautions often results in rheumatism, neuralgia, and diseases of the chest, especially among delicate people and young women.

Pupils should not be allowed to sit in the schoolroom with any outer garments on. A person who has become heated in a warm room should not expose himself to cold without extra clothing. We must not be in a hurry to put on heavy clothes for winter, but having once worn them, they must not be left off until milder weather renders the change safe. The cheaper articles of clothing are often dyed with lead or a.r.s.enic. Hence such garments, like stockings and colored underclothing, worn next the skin have been known to produce severe symptoms of poisoning. As a precaution, all such articles should be carefully washed and thoroughly rinsed before they are worn.

The Kidneys.

254. The Kidneys. The kidneys are two important organs in the abdomen, one on each side of the spine. They are of a reddish-brown color, and are enveloped by a transparent capsule made up of a fold of the peritoneum. Embedded in fat, the kidneys lie between the upper lumbar vertebrae, and the crest of the hip bone. The liver is above the right kidney, and the spleen above the left, while both lie close against the rear wall of the abdomen, with the intestines in front of them. The human kidneys, though somewhat larger, are exactly of the same shape, color, and general appearance as those of the sheep, so commonly seen in the markets.

The kidneys are about four inches long, two inches across, one inch thick, and weigh from 41/2 to 51/2 ounces each. The hollow or concave side of the kidneys is turned inwards, and the deep fissure of this side, known as the hilus, widens out to form the pelvis. Through the hilus the renal artery pa.s.ses into each kidney, and from each hilus pa.s.ses outwards the renal vein, a branch of the inferior vena cava.

A tube, called the ureter, pa.s.ses out from the concave border of each kidney, turns downwards, and enters the bladder in the basin of the pelvis. This tube is from 12 to 14 inches long, about as large as a goose quill, and conveys the secretion of the kidneys to the bladder.

255. Structure of the Kidneys. The pelvis is surrounded by reddish cones, about twelve in number, projecting into it, called the pyramids of Malpighi. The apices of these cones, known as the _papillae_, are crowded with minute openings, the mouths of the uriniferous tubules, which form the substance of the kidney. These lie parallel in the medullary or central structure, but On reaching the cortical or outer layer, they wind about and interlace, ending, at last, in dilated closed sacs called Malpighian capsules.

[Ill.u.s.tration: Fig. 108.--Vertical Section of the Kidney.

A, pyramids of Malpighi; B, apices, or papillae, of the pyramids, surrounded by subdivisions of the pelvis known as cups or calices; C, pelvis of the kidney; D, upper end of ureter.

256. Function of the Kidneys. The Malpighian capsules are really the beginning of the tubules, for here the work of excretion begins. The thin wall of the capillaries within each capsule separates the blood from the cavity of the tubule. The blood-pressure on the delicate capillary walls causes the exudation of the watery portions of the blood through the cell walls into the capsule. The epithelial cell membrane allows the water of the blood with certain salts in solution to pa.s.s, but rejects the alb.u.men.

From the capsules, the excretion pa.s.ses through the tubules into the pelvis, and on through the ureters to the bladder. But the delicate epithelial walls of the tubules through which it pa.s.ses permit the inflow of urea and other waste products from the surrounding capillaries. By this twofold process are separated from the blood the fluid portions of the renal secretion with soluble salts, and the urea with other waste material.

257. How the Action of the Kidneys may be Modified. The action of the kidneys is subject to very marked and sudden modifications, especially those operating through the nervous system. Thus whatever raises the blood-pressure in the capillaries of the capsules, will increase the quant.i.ty of fluid filtering through them. That is, the watery portion of the secretion will be increased without necessarily adding to its solids.

So anything which lowers the blood-pressure will diminish the watery portion of the secretion, that is, the secretion will be scanty, but concentrated.

The Renal Secretion.--The function of the kidneys is to secrete a fluid commonly known as the urine. The average quant.i.ty pa.s.sed in 24 hours by an adult varies from 40 to 60 fluid ounces. Normal urine consists of about 96 per cent of water and 4 per cent of solids. The latter consist chiefly of certain nitrogenous substances known as urea and uric acid, a considerable quant.i.ty of mineral salts, and some coloring matter. Urea, the most important and most abundant const.i.tuent of urine, contains the four elements, but nitrogen forms one-half its weight. While, therefore, the lungs expel carbon dioxid chiefly, the kidneys expel nitrogen. Both of these substances express the result of oxidations going on in the body.

The urea and uric acids represent the final result of the breaking down in the body of nitrogenous substances, of which alb.u.men is the type.

Unusual const.i.tuents of the urine are _alb.u.men, sugar_, and _bile_. When alb.u.men is present in urine, it often indicates some disease of the kidneys, to which the term _alb.u.minuria_ or Bright's Disease is applied.

The presence of grape sugar or glucose indicates the disease known as diabetes. Bile is another unusual const.i.tuent of the urine, appearing in _jaundice_.

The bladder is situated in the pelvic cavity or in the lowest part of the abdomen. When full, the bladder is pear-shaped; when empty, it is collapsed and lies low in the pelvis. The functions of the bladder are to collect and retain the urine, which has reached it drop by drop from the kidneys through the ureters, until a certain quant.i.ty acc.u.mulates, and then to expel it from the body.

[Ill.u.s.tration: Fig. 109.--Vertical Section of the Back. (Showing kidneys _in situ_ and the relative position of adjacent organs and vessels.) [Posterior view.]

A, 12th dorsal vertebra; B, diaphragm; C, receptaculum chyli; D, small intestines ]

In the kidneys, as elsewhere, the vaso-motor nerves are distributed to the walls of the blood-vessels, and modify the quant.i.ty and the pressure of blood in these organs. Thus, some strong emotion, like fear or undue anxiety, increases the blood-pressure, drives more blood to the kidneys, and causes a larger flow of watery secretion. When the atmosphere is hot, there is a relaxation of the vessels of the skin, with a more than ordinary flow of blood, which is thus withdrawn from the deeper organs. The blood-pressure in the kidneys is not only diminished, but the total quant.i.ty pa.s.sing through them in a given time is much lessened. As a result, the secretion of the kidneys is scanty, but it contains an unusual percentage of solids.

When the atmosphere is cold, the reverse is true. The cutaneous vessels contract, the blood is driven to the deeper organs with increased pressure, and there is a less amount of sweat, but an increased renal secretion, containing a smaller proportion of solids. Certain drugs have the power of increasing or diminishing the renal secretion. As the waste matters eliminated by the kidneys are being constantly produced in the tissues, the action of the renal organs is continuous, in marked contrast with the intermittent flow of most of the secretions proper, as distinguished from the excretions.

258. Effects of Alcoholic Drinks upon the Kidneys. The kidneys differ from some of the other organs in this: those can rest a while without any harm to themselves, or to the body. We can keep the eyes closed for a few days, if necessary, without injury, and in fact often with benefit; or, we can abstain from food for some days, if need be, and let the stomach rest.

But the kidneys cannot, with safety, cease their work. Their duty in ridding the blood of waste products, and of any foreign or poisonous material introduced, must be done not only faithfully, but continually, or the whole body at once suffers from the evil effects of the retained waste matters.

This vital fact is the key to the injurious results developed in the kidneys by the use of alcoholic drinks. These two organs have large blood-vessels conveying full amounts of blood to and from their structures, and they feel very quickly the presence of alcohol. Alcoholic liquors excite and irritate the delicate renal membranes, and speedily disturb and eventually destroy their capacity to excrete the proper materials from the blood.