Page:The New International Encyclopædia 1st ed. v. 09.djvu/503

* HAIPHONG. 451 HAIR. amountiag in IS'J'.l to ."j.'iSO.OOO tacls, is with Hong Kong. A railway to Hanoi was opened in February, 1901. HAIR (AS. hur. Icel. OHG. ha-r. Ger. Haar; Ijrdlialilv connected with (_)Cliiirch Slav, kosma, Lith. kasa, hair, and perhaps with Lat. carere, to card wool). The characteristic covering of mammals, an epidermal outgrowth, the forma- tion and structure of which are quite different from either scales or feathers. Hairs are not en- tirely wanting in any mammals, though they vary greatly in abundance, some animals being completely and densely clothed in them, while others possess them only on limited parts of the surface, as in man, and others, as adult whales, have only a few bristles near the mouth. Hairs of two distinct kinds occur in many mammals, one of which is stitT, straight, and smooth, the other curly, soft, and often minutely rough. It ■ is this roughness of the outer surface which makes the processes of felting and skinning pos- sible. When both kinds of hairs are present, the soft ones, usually called 'wool,' are much more abundant than the straight ones; but the latter give the smooth outer coat to the body and are therefore sometimes called 'contour' hairs. Un- like feathers, hairs are uniformly distributed over the body, except in special cases, where par- ticular regions are left bare. Hairs vary great- ly in size and color ; the longest hairs occur among the ungulates, especially in the tails of such species as the horse, while the shortest hairs of any mammal are usiially on the face. The color of hairs depends upon the amount of pig- ment they contain, the amount of air in the inter- cellular spaces, and the character of the external surface. Hairs arise as outgrowths of the epidermis and contain no dermal tissue. The original epi- dermal thickening pushes down into the dermis as a solid hair-germ, around which the dermis forms a hair-follicle. The hair-germ soon dif- ferentiates into two distinct parts, a peripheral and a central. The former gi^es rise to the ex- ternal root-sheath and becomes the inner, epi- dermal coat of the hair-follicle, from the outer dermal portion of which it is separated by the so-called hyaline laj'er. The central part of the hair-germ gives rise to the hair-.shaft itself and to the inner root-sheath, which closely invests the base of the shaft. The latter consists of a cen- tral medulla or pith, a cortex, and an outer cuticle ; the pith is made up of a loose, dry tissue with large intercellular spaces filled with air; the cortex is a dense layer containing the pig- ment; the cuticle is the covering of the hair, and may be smooth, or more or less rough, and orna- mented with scales and other projections. At the base of the shaft and inclosed by the swollen or bulbous base is the hair-papilla, which is well supplied with blood-vessels, and thus furnishes the nourishment necessary for the growth of the hair. When a hair is shed, a new hair may arise in the same follicle from a new hair-papilla. Each hair-follicle is provided with nerves, smooth muscles, and sebaceous glands, the latter keeping the hair oiled. By means of the muscles (arrec- tores pili) the hairs can be moved independently, but the movement of large numbers of hairs in unison is accomplished by the movements of the striped muscles of the skin. Sensations of cold, or of fear, cause an involuntary contraction of these muscles in man, causing the feeling of an erection of the hair on the head in terror, or 'gooseflesh' in cold. In the lower animals this cti'ect is produced by ill health. Hor.semen have a very graphic expression for it, saying of the coat of an animal out of condition, that it 'stares.' GROWTH OF A HAIIt. DIagraniniatio lonpitutlinal section tlirouf^h the 'root' of a hair, se. Stratum coniemu ; Nm, stratum Malpigliii; co, derma; ap, arreotoreH pili; ft, adipose tiewue; f, outer longitudinal la.ver. and f, inner transverse la.ver, of dermic coat {botii composed of connective tissue); 8cb, hair-shaft ; m, medulla; r, corte.x ; o. cuticle of shaft; W8, external root sheath ; ws', internal rool>-8heath, which reaches above onl.v as f.ar as the point of entrance of the ducts of the sebaceous viands; libd, sebaceous glands; /jp. hair- papillae <-(Mitaiiiing vessels; gli, h.valine la.yer which lies between ttic inner and outer hair-sheaths, i.e. between the root-eheath and the follicle, (Wiedersheim.) An infant's hair is shed soon after birth, and replaced by a new covering. The short downy hairs on the human body are rudimentarj' re- mains of complete hairy covering in ancestors of the race. Loss and repair appear to go on con- tinuously up to a certain time, when baldness occurs with the majority. Each hair is said to live from two to four years. The graj'ness of hair in advanced life results from a deficient secretion of pigment and perhaps an increase of air in the medulla of the hair. Well-authenti- cated cases are on record in which the hair has grown gray or white in a single night, from the influence of fear, distress, or any variety of strong mental excitement. With respect to the quantity of hair that grows on the human body, there are great difl'erences in ditTerent races. The Mongols, and other north ern Asiatics who are similar to them, are noted for the deficiency of their hair and for scanty beards, and the same character is ascribed to all the American Indians; while on the other hand, among the Ainos of Japan, or in the Kurilian race, there are individuals who have hair grow- ing down the back, and covering nearly the whole body. The Northern Asiatics and the American Indians have generally straight, lank