The second variety of tubes, those which furnish an oily-like fluid to the skin, resemble in--great part those which serve for the office of perspiration. At the extremity away from the surface of the body, each one has a gland, the oil gland, which secretes the oily material. The pores or outlets which open on the skin, however, are a good deal larger than the similar orifices of the perspiratory tubes, but they are not distributed so equally throughout the body. In certain parts of the skin they are especially numerous, as on the nose, head, ears, and back of the shoulders. The unctuous matter which is secreted by these oil glands is intended to keep the skin moist and pliant, to prevent the too rapid evaporation of moisture from the surface, and to act as a lubricant where the folds of the skin are in contact with each other. At times in these oil tubes the contents extend to the opening on its surface; the part in contact with the air then becomes darkened, and forms the little black spots so frequently seen on the face of some persons. The white, greasy matter which is thus contained within the tubes can often be squeezed out with the fingers or a watch key, and on account of its shape and black end is popularly supposed to be a grub or maggot. The tube into which each hair of the body is inserted differs materially from the two preceding, in that its function is more restricted. It serves to form a sort of sheath which contains each hair, and is called the hair follicle. Usually one of the last described ducts opens directly on the side of the hair follicle, and its secretion serves the purpose of keeping the hair pliant. It will be more convenient, however, to enter into a fuller description of the hair and hair follicle when be come to speak of the hair, the nails, and the teeth.