Encysted tumours, or wens, as they have been called, often appear to be hereditary; seldom occur single, and are met with under the surface of all parts of the body. They have been divided into different classes, according to the nature of their contents: _Atheromatous_; containing curdy matter; _Meliceritous_, containing a substance like honey; and _Steatomatous_, containing fatty matter, generally in a semifluid condition. But such terms are not adequate to express the nature of all encysted tumours; they are extremely various in their actions, and their contents vary according to the particular secretory action which the lining membrane of the cyst assumes; for the same reason, also, the contents of a tumour will differ in the different stages of its progress. Some contain a thin, fetid, brown fluid, mixed with solid particles, resembling half-dissolved fibrinous matter; in some the contents are serous, or seropurulent,—in others they are gelatinous; whilst in those which have become inflamed from external irritation, the contents are altogether purulent, or contain a very considerable proportion of that fluid; not unfrequently the cyst is covered internally by a layer of calcareous matter, to which similar particles are loosely attached. Sometimes, in consequence of irritation, organisable matter is poured out on the inner surface of the cyst, adheres firmly to its inner surface, and is often disposed in concentric laminæ. [Illustration] Sometimes, though rarely, the most prominent parts of the tumour ulcerate, and on the exposed surface is deposited a substance of semifluid consistence and gelatinous appearance, which afterwards increases in density, and ultimately assumes all the characters of horn. This hard excrescence in some instances increases only to a slight degree, and afterwards remains stationary; in others it attains a large size, and occasionally assumes a curved or tortuous form, like that of the horns of inferior animals. Horns are generally met with on the forehead, and the scalp may be said to be their seat. The largest which I have seen, measured seven inches in length, and two in circumference; but others have been removed still larger.