Sodium hydroxide is used in these cases in a saturated solution. It is best applied by means of a wood toothpick, wound about with cotton, and should be used sparingly, much after the manner in which liquid acid applications are made and as above described. A slight stinging sensation indicates that the drug has penetrated the tissues near the nerve-endings in the underlying papillae. Such symptoms render it necessary to neutralize the sodium hydroxide. According to Dr. Joseph Renk of New York City, ordinary vinegar contains just the degree of acidity necessary to neutralize the action of the sodium hydroxide, without adding a new irritating element. Verrucae may also be removed by the high frequency spark, or by electrolysis. Both of these methods are superior to cutting operations, but are equally as painful unless a drop of anesthetic solution is injected into the base of the growth, before treatment is commenced. +CALLOSITY+ +Definition.+ A callosity is a circumscribed thickening of the _stratum cornium_. The condition is usually acquired, occurring on parts exposed to intermittent pressure with counterpressure from an underlying bony prominence, as on the toes, soles, and heel of the foot, from ill-fitting shoes. Callosities are dirty-yellow to brown in color; their extent depending upon the cause; they are thickest in the centre and pass gradually into the healthy skin. Sensation is usually lost, or at least diminished, over these areas. They may interfere with movement and may have painful fissures and become infected, giving rise to abscesses, lymphangitis, gangrene, or erysipelas. Hyperidrosis is often associated with this condition. +Treatment.+ The permanent cure of callosities depends exclusively upon the removal of their causation. The position of the foot in the shoe may be faulty because of excessively high or low heels, causing callous skin to appear upon the weight-bearing surface. Occupations requiring constant standing, and deformities, also enter as causative factors which must be considered. The palliative cure rests for its efficacy on the removal of the horny tissue down to, but not into, the papillary layer. +HELOMA+ (+Corn or Clavus+) +Definition.+ A heavy thickening of the cuticle, usually caused by pressure, and producing pain by its own pressure on the tissues beneath. Though the term heloma is rarely used outside of text books, there are very few who have not had an unpleasant acquaintance with this cutaneous affection, under the name of “corns.” Heloma is undoubtedly the most frequent of all skin diseases.