=CALLUS AND CRACKS OF THE SKIN.=--Callus consists of round or irregular, flattened, yellowish thickenings of the upper or horny layer of the skin. The skin becomes hypertrophied and resembles a thick, horny layer, caused by intermittent pressure of tools, shoes, etc. The whole palm of the hand or soles of the feet may be the seats of a continuous callus. Callus is not harmful, except in leading to cracks of the skin near the bend of joints, and, rarely, in causing irritation, heat, pain, and even the formation of pus in the skin beneath. Callus usually disappears when the exciting cause or pressure is removed. =Treatment.=--The hands and feet should be soaked continuously in hot baths containing washing soda, and then should be covered with diachylon (or other) ointment. This may be done each night; or collodion (one ounce containing thirty grains of salicylic acid) may be painted, night and morning for several days, on the callus, and then, after soaking for some time in hot water, the surface should be scraped off with a dull knife and the process repeated as often as necessary to effect a cure. Fissure or cracks of the skin caused by callus are treated in the same manner: by prolonged soaking in hot water, paring away the edges, and applying diachylon ointment or cold cream to the part. Inflammation about callus must be cared for as recommended above for inflamed corns. =BOILS.=--A boil is a circumscribed inflammatory process, caused by the entrance of pus-producing germs into the skin either through the pores (the mouths of the sweat glands) or along the shafts of the hair, and in this way invading the glands which secrete a greasy material (sebaceous glands). In either case the pus germs set up an inflammation of the sweat or sebaceous glands, and the surrounding structures of the skin, and a small, red, itching pimple results. Rarely, after a few days, the redness and swelling disappear, and the pus, if any, dries and the whole process subsides. This is called a "blind boil." But usually the boil increases in size for several days, until it may be as large as a pigeon's egg. It assumes a bright-red sharply defined, rounded shape, with a conical point, and is at first hard and then softens as pus or "matter" forms. There is severe pain of a throbbing, boring character, which is worse at night, and destroys the patient's sleep and appetite. There may be some fever. The glands in the neighborhood may be enlarged and tender, owing to some of the pus germs' escaping from the boil and lodging in the glands.