The disease is rare in this country, and is seldom encountered in our experience either in dispensary or in private practice. It occurs chiefly in children, and more especially among the poorer classes. Its cause is obscure. By some authorities it is considered to be contagious, this view being more generally entertained in England (where the disease seems to be more frequently encountered than elsewhere) than in other countries. The evidence for believing it to be contagious, however, does not seem sufficient to warrant such a conclusion. Inoculation has failed to develop the disease. Some observers consider that the process has its origin in the sebaceous glands, while others—ourselves among the number—hold that it is a disease of the rete mucosum. It is to be regarded as a hyperplasia of the rete. If the tumor be cut into, the contents may usually be expressed in the form of a whitish or yellowish rounded mass of a thick or thin cheesy consistence. Under the microscope it is seen to be composed of epithelial cells with nuclei and of peculiar rounded or ovoidal, sharply-defined, fatty-looking bodies—the so-called molluscum bodies, which are to be viewed as a form of epithelial degeneration. The growth probably begins in the hair-follicles, as originally stated by Virchow and more recently confirmed by Thin.

The disease is to be distinguished from molluscum fibrosum, from papillary warts, and from acne. Local treatment, consisting of incision and expression of the contents, with subsequent cauterization with nitrate of silver, is the best procedure. They may also be ligated. As the disease tends to spontaneous cure, the remedies employed should be simple in character.

Callositas.

Callositas (syn., tylosis, tyloma, callus) is characterized by the formation of a hard or horny thickened patch of epidermis, variously sized and shaped, and of a grayish, yellowish, or brownish color. The patches are usually coin-sized, more or less rounded in shape, grayish, yellowish, or brownish in color, somewhat elevated, and of a dense and firm texture. They are most common about the hands and feet, and in a measure are protective to the more sensitive corium beneath. The ordinary surface lines are less distinct than on the surrounding healthy skin, into which the patch gradually merges. The thickening and elevation may be slight or excessive, and are most marked at the centre. The process rarely gives rise to any annoyance or pain, but when excessive the more delicate movements of the parts are restricted. Occasionally, from accidental injury, the underlying corium becomes inflamed, suppurates, and as a result the thickened mass is cast off. When occurring about the joints from motion of the parts, it may, moreover, become fissured and painful. Pressure and friction are the main factors in the production of a callosity—on the hands from the use of tools and implements, and on the feet from ill-fitting shoes. But cases are seen exceptionally in which there has been no apparent external cause; moreover, the same amount of pressure or friction in different individuals may give rise to different degrees of callosity; hence there must in some cases be other causes which at times enter into its production, as, for example, altered nerve-supply. The epidermis is the only part involved; fissuring and suppuration, it is true, involve the deeper structures, but these conditions are accidental and secondary. A section of a callosity shows a thickening of the horny layer, the corium remaining normal.

Unless the callosity is excessive or gives rise to inconvenience, treatment is rarely demanded. When advisable, the parts are to be softened by means of hot-water applications or poultices, solutions of caustic potash, or sapo viridis used as an ointment; after which the callus may be removed by scraping with a dermal curette or shaving with a sharp knife. An excellent method of treatment consists in the continuous application for some days of a plaster of salicylic acid of 10 or 12 per cent. strength, the same to be renewed every few days; at the end of a week or two the parts should be soaked in hot water, and the mass will readily come away. A solution of salicylic acid in collodion of the same strength or stronger, applied frequently for five or six days, will often act in like manner.

Clavus.

Clavus, or corn, is a small, circumscribed hypertrophy of the horny layer of the epidermis, painful upon pressure, situated usually about the feet. As commonly met with, it is about the size of a pea, with a smooth and shining surface, having a hard and horny feel. Corns are seen most frequently upon the outer surface of the little toe, but are often met with also upon the other toes and on the soles of the feet. Occurring between the toes, the moisture and friction of the part have a softening effect, and as a result the corns are soft and spongy, constituting soft corns. One, several, or more may be present. When slightly developed they cause very little disturbance or discomfort, but if large or irritated they may become sensitive and render walking painful. Continued pressure and friction, as from badly-fitting shoes, are the active factors in their production. Anatomically, a corn is a localized epidermal hypertrophy, consisting of a horny mass, cone-shaped, with the base externally and the apex pressing upon the rete and corium; the cone being made up of concentrically-arranged, closely-packed layers of epidermic cells. The corium upon which this cone-shaped mass presses may be atrophied or hypertrophied.

The first essential in the treatment is a removal of the cause. The feet should be properly fitted. The corn is to be softened by means of continuous or repeated soaking in hot water or by poulticing, after which it may be pared down or extracted. Salicylic acid, either in solution or in the form of a plaster, 15 or 20 per cent. strength, applied for several nights, will often give relief. A well-known and efficient formula is the following:

Rx.Acidi salicylici,gr. xxx;
Ext. cannabis Indicæ,gr. x;
Collodii,fluidounce ss. M.

Sig. Paint on every night and morning. At the end of several days or a week the part is soaked in warm water and the epidermic mass, or greater portion of it, is readily detached. Nitrate of silver is useful after softening of the growth has been brought about, and is also of advantage in the treatment of soft corns. Caustic potash, thirty to sixty grains to the ounce of water or alcohol, is also of service, but is to be employed cautiously. Considerable relief to the soft formation is obtained by separating the toes with a thin layer of raw cotton. A ring of rubber, wadding or felt should be employed to prevent pressure and friction upon a corn, and, as this removes the exciting cause, permanent relief may follow.