866. The third portion of the skin, the cuticle, is a thin, elastic membrane spread over the external surface of the cutis, from which it is easily detached, by the action of a blister in the living, and by the process of putrefaction in the dead body. It is without vessels and nerves, and consequently it is insensible and inorganic. It is formed as a secretion by the cutis, and is composed almost entirely of solid albumen. When any portion of it is removed, it is renewed with great rapidity. Since it is subject to constant waste from friction, and is much increased by pressure, as is manifest in the palms of the hands and the soles of the feet, its formation must be continual; yet even in the fœtus it is thicker in the parts where pressure is ultimately to be made than in the other parts of the body. 867. The cuticle is a sheath in which the body is enclosed for the purpose of restraining the organic actions which take place at its surface, and for tempering the sentient impressions received there. For restraining the organic actions it is fitted by the cohesion of its parts, which is such as to receive and transmit any fluid very slowly, as is manifest from the dryness of its surface when it is raised in a blister, and from the extreme rapidity with which the cutis dries, until it becomes as hard as parchment, when the cuticle is removed from it in the dead body. 868. Diffused over every part and particle of the cutis is the seat of common sensation, that cognizance may be taken of the presence of external objects. Restricted to particular points, the tips of the fingers, is the seat of one of the special senses, that of touch. Had the nerves which communicate to this extended surface its acute sensibility been placed in direct contact with external bodies, intolerable pain would have been the result; but by covering this surface with an inorganic and insensible substance, yet so thin that it is a pellicle rather than a membrane, the organ of sense is shielded, while the delicacy of the sensation is not impaired. But the control of the organic process and the protection of the sentient nerve are not the only offices performed by the cuticle; it serves further to hide what it is undesirable to have constantly in view. All that is beautiful in the blood as an object of sense is rendered visible through the cuticle, in the bright and rosy hue of health, at the same time that every process, the sight of which would excite anxiety or terror, is effectually concealed. 869. The skin, an organ of secretion, an organ of absorption, an organ of excretion, and an organ of sense, is thus the immediate seat of three organic processes and of one animal process.