Hair, the peculiar covering of the body of animals that suckle the young. At some period in their lives all mammals, even whales, have hair. Each hair is an outgrowth of a certain layer of the epidermis. A hair may be regarded as a sprout from the epidermis. The nearest approach to a hair is a feather, but feathers grow from the outer skin or derma. Hair takes many special shapes. The hoofs of quadrupeds are locks of hair adhering together by means of glue. The horn of the rhinoceros, the ox, the sheep, in short, all true horns are, like a hoof, modified tresses of hair and glue. The hair of the pangolin, a long-tailed anteater of Malay, assumes the form of scales, much like those of a crocodile. Fur-bearing animals are covered with dense, fine hair. Some animals are almost naked. The elephant has very scanty hair. In the case of the hedgehog and porcupine, certain hairs are enlarged and have the form of quills.
No two kinds of animals have hair alike. An expert is able to tell the difference readily. The difference between straight and curly hair is due to a difference in shape. Straight hair is cylindrical and has circular cross sections. Wavy or curly hair is flattened and has an oval cross section. The flatter the hair, the more curly it is. The hair of the sheep, that is to say, wool, as well as the hair of the beaver and certain other animals, is roughened with little scaly projections that point toward the tip and enable it to felt. All hair is composed of substantially the same material. Difference in color is due to the presence of different pigments. Human hair varies in diameter. Blonde hair is the finest; red hair the coarsest. A blonde hair is about 1/600 Part °f an inch in diameter. Red hair run's 250 to the inch. A blonde head may carry 140,000 hairs; a red head possibly not over 90,000.
Many animals, as the horse, the ox, and the fur bearers, shed their hair with regularity. The old coat is followed by a new. The long hair of the mane and tail of the horse and the tail of the ox remain unshed. In the case of man hair grows about seven inches a year, but once lost it is not apt to be restored. Each hair is nourished at its base, where new cells form, pushing the older portion farther out. Oil glands keep it moist. Certain hairs, such as the whiskers of a cat, mink, or a tiger, are reached by delicate nerves, making them serviceable as feelers.
