In the superficial view which we are taking of the anatomy of the human body, the skin may be considered as composed of two layers, the outer of which is known by various names, as the scarf skin, epidermis, or cuticle. It serves as a covering to protect the true skin beneath it. There are in this epidemis no blood-vessels or sensory nerves. The thickness of this outer skin varies, in different parts of the body, from 1-240 to 1-12 of an inch. This increase in thickness is due, in a measure, to the pressure to which these parts, as the palms of the hands, are exposed. The cells of this skin contain a pigment which is so marked in members of the African race. Absence of it makes what are called albinoes, and strange to say, albinoes are commonest among the black races. It has been suggested that this pigment in the epidermis may serve the purpose of protecting the true skin from the great heat of the suns rays. The true skin is well supplied with nerves and blood-vessels; and it is fastened to the parts beneath by a layer of connective tissue, which contains scattered through its meshes, in most parts of the body, varying amounts of fat. The hairs and the nails are growths of the epidermis; the lines which you may see on the nails correspond to the elevations on the skin below over which the nail is moulded. The hairs do not project down the skin at a right angle to its surface, but are placed obliquely, so that they incline towards the body.
Sir Erasmus Wilson thinks the hairs act partly as excretory organs, separating from the system a quantity of carbon and hydrogen, which enter into their composition. The instrument used in testing the sensibility of the skin is called an Aesthesiometer. The degree of sensibility is measured by the distance between the points at which they can be recognized as two. The following, in millimeters, are the three shortest distances at which the two points can be distinguished: Tip of tongue, 1.1; third phalanx of finger, palmar surface, 2.3; red part of lips, 4.5.
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