NVith respect to the quantity of hair that grows on the human body. there are great differences in different 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 hack. and covering nearly the whole body. The Northern Asiatics and the American Indians have generally straight, lank hair, while Europeans have it sometimes straight and flowing, and occasionally curled and crisp. Negroes present every possible gradation from a completely crisp or what is termed woolly hair, to merely curled and even flowing hair; and a similar observation holds regarding the natives of the islands in the great Southern Ocean.
The length to which the hair of the head may grow normally, especially in women, is very con siderable. A North American Indian of the Crow tribe is said to have had hair that was ten feet seven inches in length. About 1878 there was exhibited in New York City a family of Russians who were almost covered with long hair. Their foreheads, noses, and cheeks were so shaggy that their eyes could scarcely be seen, and their ears were concealed by the hair that grew from them. Cases occasionally occur where there is an abnormal abundance of hair of considerable length in women, on parts where the hair is usually little more than down. A well-known case is that of Julia Pastrana, whose ears and all parts of the face except the eyes were cov ered with hair of different lengths. The beard was tolerably thick, the hairs composing it being straight, black, and bristly, the part of it which grew on the sides of the chin hanging down like two plaits. The upper portion of the back of the neck and the hinder surface of the ears were covered with hairs. On the shoulders and legs the hairs were as abundant as they are occasion ally seen on very powerful men. See BEARD; WIG.
On the other hand, there may be a deficiency or even entire absence of hair. The effect may be more or less general or localized, and may be either congenital or acquired. It is stated that about 90 per cent. of cases of baldness (q.v.) are due to seborrhoea, which causes an excess of dandruff. This widespread affection is due to bacterial infection. The symptoms consist in the presence of small grayish-white greasy scales, falling of the hair, and more or less itching, with usually a red scalp. The primary site of the dis
ease'is, in most cases, the scalp; not infrequently, however, it extends to the face, chest, and back (seborrhceal eczema). Unless treatment is in stituted, the disease results in permanent bald ness, by interfering with the nutrition of the hair and by destroying the roots and papilla of the hair. Seborrhoea is communicable, and there fore the use in common of combs and hair-brushes should be discouraged. The treatment consists in avoiding much water as well as avoiding fre quent shampooing, and the local application of sulphur, carbolic acid, chloral, resorcin, some salt of mercury, or some other parasiticide, either in the form of an ointment or a lotion.
The services of hair in animal economy are various, though there is reason to believe that the primary use was the maintenance of a uni form body temperature by preventing loss of heat by radiation. Hair is an excellent non-conductor of heat, especially in the form of wool, and we thus find wool best developed in those mammals which are natives of cold regions. Its warmth conserving quality is largely due to the air en tangled among it. The widespread use among men of the skins of mammals in the form of furs is ample evidence of their value as non-conduc tors. An important service to man is performed by the hair about the lips and nose in keeping dust and deleterious particles from entering the nostrils and mouth, while the beard forms a pro tection to the throat and chest against chilling changes of temperature. In the form of bristles and spines, which are simply excessively stiff hairs, hair often serves a protective purpose, as in the hedgehog and porcupine. In other cases the hair becomes fused with dermal plates, and helps to form a defensive armor, as in the arma dillo and pangolin. And finally in entering into the composition of some horns, as in the rhi noceros, hair reaches the extreme of its defensive uses. In many animals, notably the cats, hairs may become organs of touch of great sensitive ness, especially in the region of the mouth. Such hairs, known as vibriss, are supplied with spe cial nerves to fit them properly for their pur pose. Whether claws and hoofs are to be re garded as modified hair is still an unsettled question. For chemical composition, see table under HORN. Consult: Walsh, The Hair and Its Diseases (London, 1902) ; Wiedersheim, Com parative Anatomy of Vertebrates (New York, 1886).
HAIR (in plants). See TRICHOME.