The true skin is richly supplied with blood-vessels and nerves, as when cut it bleeds freely, and is very sensitive.  The surface of the true skin is thrown into a series of minute elevations called the papillae, upon which the outer skin is moulded.  These abound in blood-vessels, lymphatics, and peculiar nerve-endings, which will be described in connection with the organ of touch (sec. 314).  The papillae are large and numerous in sensitive places, as the palms of the hands, the soles of the feet, and the fingers.  They are arranged in parallel curved lines, and form the elevated ridges seen on the surface of the outer skin (Fig. 103).

235.  The Epidermis, or Cuticle.  Above the true skin is the epidermis.  It is semi-transparent, and under the microscope resembles the scales of a fish.  It is this layer that is raised by a blister.

As the epidermis has neither blood-vessels, nerves, nor lymphatics, it may be cut without bleeding or pain.  Its outer surface is marked with shallow grooves which correspond to the deep furrows between the papillae of the true skin.  The inner surface is applied directly to the papillary layer of the true skin, and follows closely its inequalities.  The outer skin is made up of several layers of cells, which next to the true skin are soft and active, but gradually become harder towards the surface, where they are flattened and scale-like.  The upper scales are continually being rubbed off, and are replaced by deeper cells from beneath.  There are new cells continually being produced in the deeper layer, which push upward the cells already existing, then gradually become dry, and are cast off as fine, white dust.  Rubbing with a coarse towel after a hot bath removes countless numbers of these dead cells of the outer skin.  During and after an attack of scarlet fever the patient “peels,” that is, sheds an unusual amount of the seal; cells of the cuticle.

The deeper and more active layer of the epidermis, the mucosum, is made up of cells some of which contain minute granules of pigment, or coloring matter, that give color to the skin.  The differences in the tint, as brunette, fair, and blond, are due mainly to the amount of coloring matter in these pigment cells.  In the European this amount is generally small, while in other peoples the color cells may be brown, yellow, or even black.  The pinkish tint of healthy skin, and the rosy-red after a bath are due, not to the pigment cells, but to the pressure of capillaries in the true skin, the color of the blood being seen through the semi-transparent outer skin.

[Illustration:  Fig. 98.—­Surface of the Palm of the Hand, showing the Openings of the Sweat Glands and the Grooves between the Papillae of the Skin. (Magnified 4 diameters.) [In the smaller figure the same epidermal surface is shown, as seen with the naked eye.]]