Ordinarily a corn has the appearance of a small callosity; the skin is thickened, polished and horny. Exceptionally, however, occurring on parts that are naturally more or less moist, as between the toes, maceration takes place, and the result is the so-called _soft corn_. The dorsal aspect of the toes is the common site for the ordinary variety. The usual size is that of a small pea. They are painful on pressure, and, at times, spontaneously so. #State the causes.# Corns are caused by pressure and friction, and may usually be referred to improperly fitting shoes. #What is the pathology of clavus?# It is a hypertrophy of the epiderm. Its shape is conical, with the base external and the apex pressing upon the papillae. It is, in fact, a peculiarly-shaped callosity, the central portion and apex being dense and horny, forming the so-called core. #Give the treatment of clavus.# A simple method of treatment consists in shaving off, after a preliminary hot-water soaking, the outer portion, and then applying a ring of felt or like material, with the hollow part immediately over the site of the core; this should be worn for several weeks. It is also possible in some cases to extract the whole corn by gently dissecting it out; the after-treatment being the same as the above. Another method is by means of a ten- to fifteen-per-cent. solution of salicylic acid, in alcohol or collodion, or the following:-- [Rx] Ac. salicylici, ...................... gr. xxx Ext. cannabis Ind., .................. gr. x Collodii, ............................ f[dram]iv. M. This is painted on the corn night and morning for several days, at the end of which time the parts are soaked in hot water, and the mass or a greater part of it, will be found, as a rule, to come readily away; one or two repetitions may be necessary. Lactic acid, with one to several parts of water, applied once or twice daily, acts in a similar manner. Soft corns, after the removal of pressure, may be treated with the solid stick of nitrate of silver, or by any of the methods already mentioned. In order that treatment be permanently successful, the feet are to be properly fitted. If pressure is removed, corns will commonly disappear spontaneously. #Cornu Cutaneum.# (_Synonyms:_ Cornu Humanum; Cutaneous Horn.) #What is cornu cutaneum?# A cutaneous horn is a circumscribed hypertrophy of the epidermis, forming an outgrowth of horny consistence and of variable size and shape. #At what age and upon what parts are cutaneous horns observed?# They are usually met with late in life, and are mostly seated upon the face and scalp. [Illustration: Fig. 32. Cutaneous Horns. Showing beginning epitheliomatous degeneration of the base. (_After Pancoast._)] #Describe the clinical appearances.#