CHAPTER IX.
The Skin and its Diseases—Gangrenous Erysipelas—Lice—Leprosy—Mange—Measles—Desquamation of the Skin.
THE SKIN.
The skin of the hog, like that of most other animals, is composed of three separate parts or layers. The first or exterior of these is the cuticle or scarf skin, which covers the whole surface of the body and protects the more sensitive parts from the injuries which might result to them from immediate contact with external agents. It is a thin, tough, callous texture, perforated with innumerable holes or pores, through which pass the hairs and bristles, and whence exude those transpirations by means of which the body throws off all vapors injurious to the system. Chemical analysis has proved it to be chiefly composed of gelatine, and consequently insoluble in water of common temperature. This layer is considerably tougher and denser in the hog and other of the pachydermata than it is in the horse, ox, and most of our domesticated animals.
Beneath this is the rete mucosum, a soft expansion of tissue which overspreads, and can with difficulty be separated from the layer below it. Its purpose appears to be to protect the terminations of the blood-vessels and nerves of the skin, which it in a manner envelops or covers. This layer determines the color of the body and of the hair.
The third and undermost part is the cutis vera or true skin, an elastic texture composed of innumerable minute fibres crossing each other in all directions, fitting closely to every part of the frame, yielding by its elasticity to all the motions of the body, and interposing its dense, firm structure between the more vital parts of the system and external injuries. Innumerable blood-vessels and nerves pass through it, and appear upon its surface in the form of papillæ; it is in fact far more sensitive than the muscles or flesh.
The skin varies in density in different breeds of swine. In some of the large, old breeds it is thick, coarse, tough, and almost as impenetrable, in comparison, as the hide of a rhinoceros; while in many of our smaller breeds, and particularly in those which have a considerable admixture of Asiatic blood, and in the Chinese pigs themselves, it is soft, fine, and delicate, and bears no slight degree of resemblance to the skin of the human being. It is not to be wondered at, that a structure so delicately organised as the one we have been describing should be subject to disease. In the hog it is peculiarly so; many of the most serious maladies to which he is
