644. The cuticle is interesting to us in another point of view, as being the seat of the color of the skin. The difference of color between the blonde and the brunette, the European and the African, lies in the cuticle;—in the deeper, and softer, and newly-formed layers of that structure. In the whitest skin, the cells of the cuticle always contain more or less of a peculiar pigment, incorporated with the elementary granules which enter into their composition. In the white 296 races, the pigmentary tint is extremely slight, and less in winter than in the summer season. In the darker races, on the contrary, it is deep and strongly marked.
How can they be removed? What precaution is given? 643. Explain why those persons unaccustomed to labor, blister their hands in rowing a boat or performing ordinary manual employment for several successive hours. 644. In what other point of view is the cuticle interesting? In what part of it do we find the coloring matter?
645. The various tints of color exhibited by mankind, are, therefore, referable to the amount of coloring principle contained within the elementary granules of the cuticle, and their consequent depth of hue. In the negro, the granules are more or less black; in the European of the south, they are amber-colored; and in the inhabitants of the north, they are pale and almost colorless.
646. Color of the skin has relation to energy in its action; thus, in the equatorial region, where light and heat are most powerful, the skin is stimulated by these agents to vigorous action, and color is very deep; while in the temperate regions, where light and heat are not so intense, the lungs, liver, and kidneys relieve the skin of part of its duties. The colored layer of the cuticle has been called the re´te mu-co´sum, (mucous coat of the skin,) and described as a distinct layer by many physiologists.
Observation. “The various coloring of the inner layer of the cuticle gives to some animals their varied hues; the serpent, the frog, the lizard, and some fishes have a splendor of hue almost equal to polished metal. The gold-fish and the dolphin owe their difference of color and the brilliancy of their hues to the color of this layer of the skin.”
647. The nerves of the skin are the organs of the sense of touch and feeling. Through them we receive many impressions that enhance our pleasures, as the grateful sensations imparted by the cooling breeze in a warm day. In 297 consequence of their sensitiveness, we are individually protected, by being admonished of the proximity of destructive agents.
In what season of the year is the coloring matter less in the white race? 645. To what is the color of the skin referable? 646. Why have the races of the torrid zone darker complexions than those of the temperate or frigid zones? What is this colored layer called by many physiologists? To what is the different hues in animals owing? 647. Of what use are the nerves of the skin?
Illustration. A man who had been afflicted some years with a severe disease of a portion of the brain and spinal cord, was deprived of feeling in the lower extremities. He was directed by his attending physician to use a warm footbath. Intending to follow the directions given him, he immersed his feet in boiling water, which he supposed of a proper temperature. While his feet were immersed in the water, he experienced no sensation of an unpleasant nature. On withdrawing them, he was astonished to find the cuticle separated from the other tissues, by the effusion of serum, and thus producing a blister over the whole surface.
648. Portions of the skin would suffer every day, were it not for the sentinel-like care exercised by the nerves, by which all impressions are transmitted to the brain. As the skin is continually exposed to the influence of destructive agents, it is important that the nerves, provided for its protection, should be kept in a healthy state.
649. A large proportion of the waste of the body passes through the outlets of the skin; some portions in the form of oil, others in the form of water and carbonic acid.