The hair: its growth, care, diseases and treatment E-Book

C. Henri Leonard

• Herausgeber: Youcanprint
• Kategorie: Fachliteratur
• Sprache: Englisch
• Veröffentlichungsjahr: 2017

Beschreibung

The human hair being an ornament which it is almost everybody's endeavour to preserve inviolate as long as possible, it is explicable, why the fear of losing that ornament has become a matter of speculation of charlatanism on the credulity of the public. The best means of confounding the designs of such speculations, is the statement of real facts, distributing thus the light of knowledge. The following pages are intended to be a popular treatise, aiming at showing that the laws by which the life of the hair is governed differ not from the laws to which the body at large is subject, and that deviations of normal development must be considered—as is the case in other organs—as disease and treated as such.

Leseprobe

Contents

PREFACE

CHAPTER I. - THE CHEMISTRY, ANATOMY AND PHYSIOLOGY OF THE HAIR AND FOLLICLES.

CHAPTER II.-THE ANATOMY AND PHYSIOLOGY OF THE HAIR—(Continued.)

CHAPTER III.-THE ANATOMY AND PHYSIOLOGY OF THE SHAFT EXTERNAL TO THE FOLLICLE.

CHAPTER IV.-THE HAIR-SHAFT

CHAPTER V.-THE HAIR-SHAFT—(Concluded.)

CHAPTER VI.-THE COLOR OF THE HAIR.

CHAPTER VII.-HAIR IN SINGULAR PLACES.

CHAPTER VIII.- HYGIENIC TREATMENT OF THE HAIR.

CHAPTER IX.-POLYTRICHIA.

CHAPTER X.-CANITIES.

CHAPTER XI.-TRICHONOSIS DECOLOR.

CHAPTER XII.-ALOPECIA.

CHAPTER XIII.-COLORING, OR DYEING, THE HAIR.

CHAPTER XIV.-PITYRIASIS.

CHAPTER XV.-SEBORREA CAPILLITII.

CHAPTER XVI.-ASTEATODES AND ALLOSTEATODES.

CHAPTER XVII.-ECZEMA.

CHAPTER XVIII.-SYCOSIS MENTI, ACNE AND RUPIA SYPHILITICA.

CHAPTER XIX.-DERMATOPHYTIC DISEASES IN GENERAL.

CHAPTER XX.-TINEA TONSURANS (RINGWORM OF THE SCALP).

CHAPTER XXI.-TINEA FAVOSA.

CHAPTER XXII.-TINEA DECALVANS.

CHAPTER XXIII.-TINEA SYCOSIS.

CHAPTER XXIV.-DERMATOZOA.

CHAPTER XXV.-THE DERMATOZOA (concluded).

CHAPTER XXVI.-DIFFERENT MODES OF DRESSING THE HAIR.

CHAPTER XXVII.-THE HAIR OF THE ANCIENT ASSYRIANS, EGYPTIANS AND PERUVIAN INCAS.

CHAPTER XXVIII.-THE BEARD.

C. Henri Leonard

The hair: its growth, care, diseases and treatment

First digital edition 2017 by David De Angelis

PREFACE

The present work has engaged the attention of the Author for the past six years. It is intended simply as an introduction to a second and larger and more scientific work that the Author hopes, in the near future, to have time to prepare. The purpose of the larger work is to show the possibility of the classification of animals from the differences in the microscopical structure of their hair-shafts. He has examined the hairs from a very large number of the different animals of the globe, specimens of which he now has in his possession, and believes such a classification possible.

This treatise is of as much value to the laity as the profession, hence he has avoided, as far as possible, purely technical terms, and has also translated each prescription into its English equivalents.

Numerous authorities have been consulted, and their text and illustrations have, in many instances, been altered to suit the views of the Author, and so used, or else have been copied entire. While it is impossible to here mention all the names, yet the Author feels himself under special obligations to the following works and authors: ANTHON, ARISTOTLE, BEAL, BENNETT, THE BIBLE, BOGUE, BULKLEY, COTTLE, DARWIN, DUNGLISON, ENCYCLOP ZEDIA METROPOLITANA, FLINT, JR. , FOX, FRY, GODFREY, GOSSE, GRAY, GROSS, HAECKEL, HERODOTUS, HOMER,HORACE, KIRKE, DITTO & BOND, KÖLLICKER, KURS, LARRY, LAYARD, LIVINGSTONE, LUBBOCK, MARTIAL, NAYLER, NEILL & SMITH, NEUMANN, OVID, PIFFARD, RA WLINSON, RAYNALD, ST. JOHN, THE TALMUD, TANNER, VERRILL, VIRGIL, WELLS, WILSON, WITHOF and THE ZEND AVESTA. In most instances the authority quoted will be found named in the text.

DETROIT, 52 Lafayette Ave., January, 1880.

CHAPTER I. - THE CHEMISTRY, ANATOMY AND PHYSIOLOGY OF THE HAIR AND FOLLICLES.

Hair, though seemingly a small and unimportant subject, when but a single shaft is considered, is, withal, one that much can be said about.

As a commercial commodity, hair is of vast importance. Thousands of people, from the wealthy wig-seller, whose customers are of royal birth, down to the poor peasant girl who grows her locks but to be shorn—for the girls of Brittany and the lower Pyrenees repair annually to their fairs in droves, each in turn surrendering her rich long hair, hanging down to her waist, to the buyer's shears—make a fair amount of their living from traffic in this material. Fashionable Paris alone, and London as muchmore, consumes annually over one hundred thousand pounds of human hair in the manufacture of her chignons and wigs, an amount that would load down, from its-bulk and weight, twenty of our largest freight cars. Just think of this for a moment; two cities alone consuming annually two freight-train loads of human hair! What must be the amountwhen we take into consideration that used by the cities and towns the world over ? As the weight per head averages from one-half to three-quarters of a pound, it is quite easy to see how many individuals sacrifice their cranial coverings upon this altar of mammon annually.

Convents usually furnish a large amount of fine, luxuriant hair for the French, Spanish and Italian markets, and it is known to the trade as " church hair."

Black hair comes usually from Spain or Italy; golden hair from Germany, and yellow from Holland. In England the red hair comes from the Danish descendants of the northern counties; the black, or bluish-black from the Celtic descendants of Wales; the brown, with a shade of the flaxen, from the Saxon element in the south.

The quantity of long black hair from a French head averages about five ounces; the hair from an Italian about six ounces; from a German, about ten ounces.

The prices paid for hair average usually from five dollars per head, down to twenty cents, all depending, of course, upon the quality and color of the material. Some unusually fine heads bring double or triple this price, and some heads of rare qualities are fairly weighed against gold.

Golden hair is one of the most valuable colors in the English market, bringing as high as two dollars per ounce, if of fine quality. A fine article of white hair sometimes sells as high as five dollars an ounce. The dealers detect the quality of the hair by the touch and smell. Indeed, some nationalities have an odor to their hair peculiarly their own, as notably that of the Chinese, whose hair has a musky smell; certain diseases will develop an ammoniacal odor to the hair as well as the perspiration; the odor of violets has also been distinctly noted in one or two cases: the sense of touch enablesthem to judge of its smoothness, evenness and fineness: the sense of smell enables them also to judge whether its color has been tampered with by dyes or bleaching agents, and how it has been packed for market; sometimes, also, whether it was from a living body or from one in the charnel house.

As a rule, the hair-growers are a degraded race of people, filthy in their habits, living in low mud huts, and wearing but excuses for clothes. Closely fitting caps are worn by them, to protect the hair from injury, and also to avoid the necessity of pinning it up or frequently combing it, as either of these procedures would endanger its breakage, or the straining of the roots of the hair, and so get, by these means, an uneven or imperfect growth. Their riches consist not in their flocks, but rather in the hirsute growth that they themselves may produce.

THE CHEMISTRY OF THE HAIR.

By chemical examination we find the hair to be composed of the same elements (and in nearly the same proportions) as are found in the horns and hoofs of animals, the baleen or bone from the mouth of the great sea monster, the whale, the nails and feathers of fowls and birds, the nails of our own fingers and toes, and even the outer or epidermal layer of our skin. The resemblance of these several bodies in their chemical composition is as similar as their physiological formation. Besides the animal matter which they all contain in common, we find this to be the result of the analysis of each:

It will be noticed that there is but little more variationbetween the chemical analyses of the different substances given than there is between the two different analyses of the hair itself. Thisvariation is in part due to the fact that no two heads of hair are exactly alike in their chemical composition; they vary much with the color of the hair too. Thus, for intsance:

Brown hair gives us the largest proportion of carbon, while sulphur, oxygen and hydrogen are found in a smaller ratio.

In black hair we find a larger amount, comparatively, of oxygen and sulphur, but a smaller amount of carbon and hydrogen.

Fair hair is the richest in oxygen and sulphur, but has less carbon and hydrogen than hair of any other color.

In red hair is found a reddish oil, a small quantity of iron, but a large quantity of sulphur.

White hair, besides the sulphate of alumina, yields the phosphate of magnesia, a whitish oil, and, in the aged, a large amount of the phosphate of lime.

The beard gives us more carbon and hydrogen than the head hair, but less oxygen and sulphur; the quantity of nitrogen is, however, about the same.

Upon the variation of the amount of these different chemical-- constituents present in hair of a given color, depend the different shades of color caused by the use of the same dye, as spoken of in the chapter devoted to the consideration of hair-dyes and bleaching agents.

The peculiar offensive odor noticed on burning hair is due to the decomposition of its nitrogenous or animal substance, called keratin, thus setting the previously combined sulphur free. This substance, which goes to make up the bulk of the hair, is soluble in alkalies, with the formation of ammonia, and strong sulphuric acid; but insoluble in boiling acetic acid, which dissolves the nails, horn and epidermis, and hence distiriguisheshair from these very similar products. Liquor potass also dissolves it quite readily.

When hair is reduced to ashes, by burning, the ash is found to yield calcic sulphates and phosphates, ferric and manganesic oxides, and ferric silicates; the ash from white hair yields sulphate of alumina and lime, and phosphate of magnesia.

ANATOMY AND PHYSIOLOGY.

Hairs are an appendage of the skin, the same as are the nails; both are but modifications of the epidermal or surface-layer of the integument. In this respect also resembling the claws and feathers of birds and fowls, the claws, hoofs and horns of animals, the scales of fishes, and the tough, overlapping mail of the alligator and crocodile.

Hairs are found everywhere, as a rule, upon the human body, excepting upon the palms of the hands and fingers, and the soles of the feet and toes; though none are found on the upper eyelids, on the pulp of the lips, the dorsal surface of the tips of the fingers and toes, inner surface of prepuce, on the glans penis, mucous surface of the labia, mucous surfaces generally, and the globe of the eye. To this last, however, I know of a noted exception among the animals, that of a calf born with a hair-tuft springing directly from the front of the eyeball.

Hair is found also on or within many of the internal organs, and notably so in pathological formations, or tumors, of the ovary. In the normal state these hair-growths are microscopical, being only cilia in most instances. Upon the inside of some of the ovarian cysts, though, I have seen it in large tufts, or handfuls, growing luxuriantly from the cyst-wall.

_ Hairs vary in length, size and color in different individuals, and also according to the place whereon they are found in the sameindividual. Thus, on the backof the fingers they arevery short, and shorter still on other portions of the body, where the microscope is necessary to reveal them, as they barely reach out of the skin-follicle containing them. On the head they become of great length, in some instances, as I shall give further on, trailing on the ground. The beard and eye-lashes are remarkable for their comparatively great size; the former, in some individuals, grows also to be of greatlength, as for instance that of the authentically recorded case of the Burgomeister Hans Steiningen, whose beard was so long that he trod upon it one day, when ascending the stairs to the council chamber, and so stumbled and fell down and was killed.

Hairs are cellular in structure, being made up of an aggregation of cells, that are variously shaped and altered from their primary spherical condition.

Hair begins its growth by the formation of a follicle, through a downward budding-like process, from the corpus or retemucosum, the middle layer of the skin,.thus: In Fig. 1, E represents the epithelial or outer layer of theFig. 1.skin, the scarf-skin,in other words; R. M. the middle layer or rete mucosum; C corium, or true skin.

The hair follicle is formed early in intra-uterine life. As early as the third month of fcetal existence the involution of the skin commences, and with it the papilla and the commencing hair-bulb are seen. When further advanced in the formation, the follicle will assume the appearance, on microscopical examination, of that seen in Fig. 2. This represents a cross-section of the follicle at the 16th week ofembryonic life, represents the external skin layer (E of fig. 1); 2, the rete mucosum (R, M, fig. 1); 4, the hyaline membrane of the follicle formed the corium (C, fig. 1); 3, 3, 3, represent the original spherical and ovoid cells of the rudimental hair. The eyebrows, supercilia, and the hairs upon the forehead, are the first to begin their growth, then those of the upper lip and those around the mouth are the next in order given, are the hairs of the scalp, back, chest, fingers, external ear, and, lastly, those on the end of the nose. By the end of the sixth month of foetal life, the body hair is visible. The infant, at birth, is covered with a fine downy growth, that Larry has likened to the bloom upon fruit. This is all shed in time, and hair of new growth, or extra-uterine development, take their place.

THE FORMATION OF THE PAPILLA, BULB AND SHAFT

The formation of the papilla, bulb and shaft in this way: the mass of cells, 3, 3, 3, fig. 2, divide themselves by aggregation into three portions; those nearthe edge of the hyaline membrane or envelope, 4, flatten out and go to form the internal root-sheath of the hair,the central mass come more compaetlytogether, deepen in color and go to form the bulb of the hair at its lower portion, and the shaft at the upper portion; those in the lowest portion of the follicle go to form the papilla. Originally, none of these cells can be distinguished from the other cells of this same skin-layer. Diagrammatically, then, we would have about this condition of affairs: fig. 3, 1, representing the internal root-shealt.

The hair papilla is not unlike the many other papillae found in the corium to which it is intimately attached, and from which it receives its nourishment.

The height of the papilla is always greater than its breadth, being about double it; the average being about the 1/100 ofan inch on perpendicular section. Each papilla is made up of undeveloped, nucleated connective-tissue cells commingled with a few free fibres. It is from these microscopic organs that the hairs of our bodies derive their nourishment and elements of growth.

The formative cells are continually being pushed upwards from the soft bulbs of the hair, taking with them the coloring granules; they then arrange themselves about the centre of the shaft forming itspith, and part of the fibrous portion. Then, from the combined action of the hair bulb and the hair follicle, new aggregations of cells are made, which, as they are elevated to the surface of the skin, are contracted and flattened to the shape that we find them in the shaft without the follicle. The growth of hair, then, being but the gradual pushing upwards (out of the follicle) of previously-formed cells by the new ones that are being formed continually below them. This explains why-the hair will grow after it is plucked out " by its roots." So long as theyapilla, with the follicle, is in a healthy condition, so long will a new hair be ready to spring up from the same follicle. Thus in the case of eye-lashes, they are renewed in 150 days.

To return now to a further description of the follicle. Each one is from 1/12to of an inch in depth. As they are formed by an induplicature of the skin, their lining membranes partake, of necessity, of similar connective tissues and epithelial elements. From minute and careful microscopical investigation, it has been found that there are three distinct (from their cellular arrangement) membranes, going to form each follicle, after the indenture in the corium has been made by the downwardly budding rete mucosum; (Fig. 3.) The outer membrane, Fig. 4, 6, is made up of fusiform, connective-tissue cells, arranged

longitudinally, with elongated nuclei, and is from the1/2000 to the 1/1000.

In this layer there is also found free capillary circulation, with a tendency of the vessels to cross the membrane transversely. The inner membrane lining the follicular depression, and which surrounds the hair, represented by Fig. 4, entirely, though it is not represented in the cut, the limiting or hyaline membrane,It is freely supplied with nerve fibres have been discovered in it. The middle membrane is nearly triple the thickness ofas it is sometimes called. It is not readily acted on by acids and alkalies, hence differs very materially from the other follicular membranes. Between it and the middle layer is a lymphatic plexus, and, in the case of tactile hairs of animals, notably those of the feline class, there is a highly developed vascular plexus. Running downward from this hyaline membrane, continuing in the same direction as the follicle, as in the case of the longer and larger hairs, there is a stalk-like projection seen passing through, and below, the true skin-layer into a subcutaneous connective-tissue layer, there uniting and inosculating with its fellows.

The hair follicles, in the majority of instances, do not descend perpendicularly into the skin, but take an oblique course. This gives a "set" to the direction which the hair-shafts take when out of the body, and which will be treated of further on.

THE SEBACEOUS GLANDS.

Each hair follicle has one or more sebaceous glands emptyinginto it near its outlet; these glands may be either simple, Fig. 4, 11, page 18, or compound, 9, of same figure. From these glands are poured out the oily material that goes to lubricate the follicle, hair and scalp. The " dandruff " seen upon the scalp is a production of the dried material from these glands, commingled with the dust and filaments of the clothing that find lodgment in the hair, together with the exfoliation of . the scarf-skin of the scalp. Besides these sebaceous glands there are sweat glands also opening into the follicle.

THE MUSCLES OF THE FOLLICLE.

Referring again to Fig. 4, page 18, there will be noticed, on the right-hand side of the plate, two bands of muscular tissue, 7 and 8, running diagonally upward from the lower portion ofthe follicle. These are called erectores pill, the erector muscles of the hair. By the contraction of these muscles thehair is elevated, with its follicle, and protruded from the skin, giving the condition of affairs known as "goose pimples " or " goose skin " (cutis censerina.) Through the same physiological action upon the hairs and follicles of the scalp, one's hair is made " to stand on end," as is popularly said. During the contraction of these muscles the contents of the follicle and the sebaceous glands are also squeezed out more abundantly than when the follicle is in its usual distended, or quiescent, state. It is these muscles that also give the tactile movements to the " whiskers " of the feline, canine and leonine species, only they are more developed in them than in man.

CHAPTER II.-THE ANATOMY AND PHYSIOLOGY OF THE HAIR—(Continued.)

THE ROOT-SHEATHS.

Investing the roots of the hair are two layers of cells, or membranes, called the outer and inner root-sheaths.

The external sheath, 4, Fig. 4, is continuous with the bulb of the hair, and resembles, closely, the rete mucosum (Figs. 1 and 3), from which it is formed. It is made up of numerousrounded and nucleated cells, which vary from the1/4000of aninch to the1/800of an inch in diameter. Those situated nearer to the surface of the hair cylinder are somewhat flattened. This sheath is three or fourtimes thicker than the innerroot-sheath.

The internal root-sheathis more transparent than itsfellow, the outer, and seemsto be made up of two layersof flattened cells; the layer, 1, Fig. 5, lying adjacent to the hair cylinder, is of non-nucleated, elongated, transparent cells, varying fromthe 1/1000 to the 1/15.Tly of an inch

in length, and is known as Henle's layer. The outermost layer, 2, is known as Huxley's, and is made up of nucleated polyhedral cells, with axes parallelto the shaft of the hair. These are also transparent, and are not so compressed as those forming Henle's layer, and their longitudinal axis is shorter. At 3, same figure, is shown, in contrast, some of the cells from the external root-sheath. At the bottom of the follicle there is only one layer of the nucleated cells forming this sheath, and, similarly to the outer root-sheath, it ends near the entrance of the ducts of the sebaceous glands.

A transverse section of a hair and its follicle,at the middle of the follicle, would show all the different layers and membranes we have gone over in the following order (Fig. 6): 1 is aportion of the hair; 2, the epithelial layer of the hair shaft; 3 and 4, the inner and outer layers of the internal root-sheath; 5 and 6, the thick, outer root-sheath with its two different layers of cells, the outer lying transversely to the long axis of the follicle; 7, 8, 9, the hyaline membrane, with its inner, middle andouter layer of cells; 10, the pith or medulla of the hair, which is to be described on a following page.

THE HAIR BULB OR ROOT.

That portion of the hair below the surface of the skin is called its root. It presents a bulbous enlargement at this point, and hence is frequently termed the bulb. This is the part that furnishes the sustenance to the existing hair shaft without the follicle. It is larger, whiter and softer than the portion, without the skin, and has a hollowed-out base, which rests upon the papilla springing from the bottom of the follicle, and is connected with it by the interlacement of the cells forming the papilla and the bulb proper of the hair.

An examination of the structures of the root of the hair isbest made by chromic acid prepalular structures so they can bebulb proper, throughout its entire mass, with the exception ofa thin cortical covering, we findthe same round, nucleated cells seen in the external sheath ladenand shown at 3, Fig. 5. Theyare also seen in Fig. 7, at 6 and 8. Sometimes these cellsare pigmented, especially in theupper shaft portion; they go to make up the fibrous part ofthe hair, 10, and the medullary portion, 8, as they are further developed. They first become, with their nuclei, elongated for the cortical portion, 5, and this process continues till they are still further narrowed and lengthened, and their nuclei become but thread-lines or are lost entirely. The cells overlap each other closely, and somewhat regularly, and in a healthy hair-cylinder it is impossible to separate them without chemical reagents, of which sulphuric acid is the best. This layer will be further treated of When we come to speak of the shaft of the hair, for, in the attenuated and hardened state of the cells. it is continued on to the tip of the hair without the follicle. The length of these cells, in their mature state, ranges from theto the a of an inch, and their width from the1/300to the1/1000of an inch. Between the plates of this layer are found granules of pigment matter—forthis is the layer that gives the color to the hair—and also a few narrow air chambers.

The axillary and medullary portion of the hair (8 and 11 of Fig. 8) is the most recent formation from the papilla-

In thenotice it is intimately connected with it. In young hairs this portion of the hair is not found, all the material going to form the fibrous and epidermal portion. The cells that go to make this up are the same as those found in the newly-formed portions of the fibrous part just described;the same as are also found in the papilla. As the hair is pushed gradually upwards, by the newly-forming cells below, they shrink up, become less regular in form, lose their nuclei, and leave vacant spaces between their walls for quite a large supply of residual air.

The portion marked 5 in Fig. 7, is the outside or epidermal layer of the hair. Its origin, 4, is also in more or less spherical, nucleated cells, in common with the root-sheaths, which, as they are pushed further and further from the follicle, become flattened, lose their nuclei, and finally lie in imbricating layers, covering the entire circumference of the hair shaft. They are thin and transparent, when fully matured, and require the use of caustic soda solutions, or sulphuric acid, to separate them from their fellows, and show their form and structure. Their size varies from the WiT, to the „1, 0 of an inch in diameter.

Of the remaining portions of Fig. 7, 1 represents the hyaline membrane, or outer follicular layer; 2, the external root-sheath; 3, the internal root-sheath;7, the papilla.

EXIT FROM THE FOLLICLE.

At the first formation of the hair-cylinder it does not issue point first from its follicle, but it is bent over upon itself, so that a loop is formed;this loop gradually pushes its way through the follicular opening, and then, from its elasticity, the shaft straightens itself out. Indeed, it is the law of almost all growths, that the point does not issue direct from the parent-cell or follicle, but is bent downwards till the exit-making loop is formed. This you witness in the fullest degree in the growthof plants from their seeds. Sometimes, for various reasons, prominent among which is the sealing of the follicle withsebaceous matter, or its being covered over by the scales of the scarf-skin, or the outer walls adhering together, the hair cannot make its exit at all; in this case it keeps on its growth—for the papilla, as long as blood is sent to it in proper condition, never ceases its work—and doubles more and more upon itself until the follicle is fully distended. This produces intolerable itching, and hence attention is directed to the seat of the malady.

The imprisoned hairs are readily set at liberty by the use of strong alkaline washes (strong soap-suds is as good as anything), and frictions with coarse towels. The condition can also be recognized by the sight, the coiled hairs showing themselves as little black spirals beneatb the skin. Occasionally the hairs will be found to be one-half an inch, or more, in length when released. Sometimes a whole limb may be thus affected. Aristotle (384 to 322 B. C.) has described the condition quite fully, although it is quite a rare malady.

SHEDDING AND REGROWTH OF HAIR.

In the former chapter wespoke of the shedding of the foetal hair. This process, with the regeneration of thehair, was first noticed by theGerman physiologist Kolliker. A diagram will perhaps aid us in more completely understanding this physiological process, see Fig. 8. In this, 1 represents the eyelash of a child that was of intra-uterine growth, and is now about to be thrown off; 2 is the bulbous portion of the old hair severed by the constricting follicle, 3, from its papilla, 5;the new hair, 4, is just beginning to be formed, and is graduallypushing the old one out of the follicle; 6 is a sebaceous gland, with its short duct emptying into the hair-follicle.

The natural loss of hair, either through disease or the age of the hair itself, is through this same way, when the papilla is left uninjured.

As a first step to this process there seems to be a fatty degeneration of the cells at the summit of the papilla, induced either by improper blood-supply or through some slight injury, as pulling the hair. Since it is the tendency of the follicle to keep contracted, of course, if the cellular elements are diminished for a time, a constriction must necessarily take place; when once started, the nourishment of the hair is so materially lessened by the severing of the connection of the root-sheaths, which the constriction causes, that the hair must become ultimately separated from all nourishment, and hence supplanted by one of more vigorous and healthy growth.

The shedding of the hair-coats of our domestic animals, and the moulting of our fowls and birds, is from a similar physiological cause. The hair shaft has lived its life, the cell formation is not sufficient to keep so long a hair in a live, or growing, condition, so the old hair is thrown out of the follicle by the new growth forming below.

CHAPTER III.-THE ANATOMY AND PHYSIOLOGY OF THE SHAFT EXTERNAL TO THE FOLLICLE.

We have come now to the consideration of the hair-cylinder as it exists without the follicle. Usually there is but one shaft having exit from the same follicle, yet two or more are sometimes seen.