4. The cutis, or true skin, lies beneath the epidermis, and is its origin and support. It is firm, dense, elastic, very sensitive, and is freely supplied with blood-vessels. It is closely connected with the tissues below it, but may be separated by means of a sharp instrument. The surface of the cutis is not smooth, but is covered here and there with minute elevations, called _papillæ_. These are arranged in rows, along fine lines, or ridges, such as those which mark the palm and fingers; their number is about 80 to the square line (a line being one-twelfth of an inch). These _papillæ_ contain the blood-vessels which carry the supply of blood needed by the ever-wasting skin. They contain nerves also, and are largely concerned in the sense of touch; hence they are particularly abundant where the touch is most delicate, as at the ends of the fingers. [Sidenote: 5. What are the nails and hair? The growth of the nail? The rapidity of its growth? Accident to the nail?] {43} [Illustration: Fig. 14. _a, b._ THE ROOT OF A HAIR. 1, 2, 3. The skin forming the hair sac. 4. Sebaceous glands. 5. The hair sac. _c._ TRANSVERSE SECTION OF A HAIR.] 5. THE NAILS AND HAIR.--These are appendages of the skin, and although very unlike the cuticle as it appears on the surface of the body, they are, in reality, modified forms of that layer of the skin. The nail grows from a fold of the cuticle at the root, and from the under surface. As fast as it is formed, it is constantly being pushed outward. The rapidity of its growth can be ascertained by filing a slight groove on its surface, and noticing how the space between it and the root of the nail increases, in the course of a few weeks. When the nail is removed by any accident, it will be replaced by a new one, if the root be not injured. [Sidenote: 6. How are the hairs produced? Difference in their length?] 6. The hairs are produced in a similar manner; the skin forming depressions, or hair sacs, from the bottom of which they grow and are nourished (Fig. 14). They are found, of greater or less length, on almost all parts of the surface, except the palms of the hands and soles of the feet. On certain parts of the body, they grow to great length; on other parts they are so short, that they do not rise beyond the hair sac in which they originate. [Sidenote: 7. Root of the hair? Shaft? Firmness and softness of the hair?] 7. The bulb, or root, from which the hair arises, is lodged in a small pouch, or depression in the skin. The shaft is the part which grows out beyond the level of the skin. Its growth is altogether in one direction, in length alone. The outer part of the hair is quite firm, while its {44} interior is softer, and probably conveys the fluids by which it is nourished. The hair is more glossy in health than at other times. [Sidenote: 8. Office of the nail? Of the hair? Give the illustrations.]