That portion of the hair in the skin is called the root and the part external to or beyond the skin surface is called the shaft. The study of normal mature hairs resolves itself into a consideration of the follicle, the bulb the shaft and the papilla.
The hair-follicle is a sac-like depression in the corium in which the bulb of the hair is firmly implanted. The direction of the follicle as well as the contained hair is always at an oblique angle to the plane of the cutaneous surface. The hair-follicle consists of the lower two-thirds of that part of the hair which is found in the skin and the coverings of the hair known as hair- sheaths. The outer or external root-sheath (the prickle layer of the hair- follicle) consists of a turning inward of the rete and lines the whole follicle. It is thinnest at the base and the neck of the hair-papilla, consisting in these locations of one or two rows of cells. It is several times thicker than the root-sheath proper and is thickest at the middle of the follicle. This sheath practically forms a hollow cylinder which contains the hair and its envelopes.
The inner or internal root-sheath (also known as the root-sheath proper) of the hair was formerly considered as divided into two layers, Henle’s and Huxley’s. These are not distinct layers but rather, as Macleod says, “only parts of a single layer, so modified by differences in tension and pressure and by the presence of more or less keratohyalin in their cells, as to suggest that they have had a different origin.” The inner root-sheath is composed of grandular polyhedral epithelia which, in the inner parts, become somewhat elongated, coarsely granular and nucleated. The inner root-sheath covers the papilla, forms the bulb or the root of the hair and extends upward to the neck of the follicle. According to Heitzmann, the hair is produced by this sheath alone, by a solid elongation of the epithelia. The inner root-sheath is separated from the outer root-sheath by a thin membrane. Unna asserts that between the inner root-sheath and the main mass of the hair there is found the matrix from which both the cuticle of the root-sheath and the cuticle of the hair are formed. The cells, forming the cuticle of the root-sheath, are arranged with their axes on a line with the circumference of the hair, while the cuticle of the hair is composed of cells which gradually become columnar in shape and lie parallel with the length of the hair.
The hair-bulb or root of the hair embraces the papilla and is in turn surrounded by the hair-follicle. It is composed of three structures, the cuticle, the cortex and the medulla. The thin outer covering or cuticle is a transparent membrane, composed of non-nucleated, imbricated lamellae. As the root nears the surface, the cuticle of the hair appears to be formed of imbricated scales with elevated edges which, in the shaft of the hair, gives it the characteristic serrated appearance. The cortical mass or main body of the hair is composed of delicate, flat, nucleated, firmly attached, fusiform scales which give to the hair its great strength and elasticity. These qualities are further assured in the larger hairs by a central marrow or medulla, which is composed of loosely packed embryonal corpuscles, fatty and pigment matter, and extends from the root of the hair to its point. It is now generally believed that what was formerly thought to be pigment and fat, are in reality air- vesicles.
The shaft of the hair extends from the place of cutaneous exit to its free extremity. When uncut and healthy, the latter always ends in an acuminate point, well illustrated in the hairs of normal eyelids. Previous mention has been made of the color, caliber, length and straightness or curl of hairs in different individuals. The structure of the hair-shaft, in that it presents cuticular, cortical and medullary elements, is similar to the make-up of the hair-root, minus the root-sheaths. The flattened plates of the cuticle are non-medullated, non-pigmented and overlaid, like adherent fish-scales. The cells of the cortex, composing its bulk, are nucleated, pigmented and fusiform. The medulla is wanting in the lanugo hairs and is best developed in the strong hairs of the beard and eyelashes.
The hair-papilla is composed of a delicate fibrous or myxomatous connective tissue, freely supplied with pigmented and non-pigmented connective tissue corpuscles and a variable number of blood-vessels. Papillae are club-shaped or spherical formations, arising from the corium and expanding into the hair-bulbs. They are nearly twice as long as they are broad and their breadth, according to Robinson, is in direct proportion to the length of the hairs.
Normally a hair has a limited existence and is shed by a process of separation which takes place about the bulb, accompanied by a contraction of the hair- follicle at this point. The new hair is regenerated from the inner root-sheath about the papilla and, as it grows, pushes the dead hair before it until it is shed or accidentally removed by traction from without. Hair is not only derived from the epidermis but its production is a process that forms a cornified cylinder, which is projected from the cutaneous surface and is very analogous to real epidermal cornification.
NAILS
Nails are dense, horny, translucent, elastic, concavoconvex plates derived from the epidermis and imbedded in the corium on the dorsal aspect of the distal phalanges of the fingers and toes. The convex surface of the nail is exposed while the concave is implanted on the nail bed beneath. They appear from without to be curved downward from side to side and less markedly so from the root to the anterior or free edge. This latter, if uncut, extends beyond the end of the fingers or toes. The nail consists of horny epithelia like the corneous layer of the epidermis, only more dense in structure. According to Bowen, the nail is a modification of the stratum lucidum. About the third month of fetal life, two or three rows of epithelia from the mucous layer appear at the site of the future nail-root. In the fourth month one or two additional rows of epithelia are projected between the first. As these cells mature, they are gradually forced forward between the rete mucosum and the horny layer of that part of the epidermis which becomes the nail-bed. By the beginning of the seventh month, the nail pushes its way through the corneous layer and at the end of intrauterine life is usually well developed.
Various terms are applied to designate the anatomic portions of the nail and the surface upon which it rests and grows. Thus the nail proper or uncovered part is known as the nail-body while the imbedded portion is called the nail- root. The matrix is that portion from which the nail grows. It extends from the floor of the nail-fold at the root as far forward as the anterior convex border of the lunula (that portion of the matrix not concealed by the nail-fold), represented externally by the relatively light-coloured part of the nail. The derma of the matrix is composed of dense fibrous tissue, which is blended with the periosteum of the last phalanx beneath and rises above into rows of papillae parallel with the long axes of the fingers and toes. These papillae decrease in size as they press forward and are the least developed at the lunula. The stratum mucosum rests on the papillae and in the furrows between the rows, and these epithelia are gradually transformed into horny epithelia. According to Unna the most posterior part of the matrix produces the horny plates of the nail-surface; the middle of the matrix, the middle of the nail; and the anterior part of the lunula, the deepest part of the nail.
The nail-bed, which is the substance supporting the nail as it is pushed forward from the matrix, extends from the anterior border of the latter to the beginning of the free part of the nail. It is composed of subcutaneous tissue firmly attached to the periosteum beneath, ridges of papillae from the corium running the full length of the nail-bed, and prickle cells of the mucous layer so arranged over the papillae and their interspaces as to present a grooved appearance to the upper surface of the nail-bed. Into these grooves corresponding ridges on the under surfaces of the nail fit, thus giving firm attachment of the nail to its bed.
The nail-fold or nail-wall is crescentric in shape, clasping the nail posteriorly and laterally. It consists of the skin in which rests the border of the nail not set free by the process of growth. Its deeper part is continuous at the root of the nail with the matrix and laterally with the nail-bed. The resulting depressions between the matrix and nail-bed and the overlapping skin is known as the nail-groove. The layer of cuticle, extending forward from the nail-fold over the body of the nail posteriorly, is called the nail-skin or eponychium. The epidermis bordering the whole nail is called the perionychium and the epidermis upon which the nail rests the hyponychium.
American homeopath, he directed several hospitals in New York.
Professor of dermatology.
Served as Lieut. Colonel during the 1st World War.
See his book online: American homeopathy in the world war