Aphthæ are small whitish ulcers, usually commencing as vesicles, on the surface of a mucous membrane. The whitish substance generally contains large quantities of a minute fungus, Oidium albicans. They are painful, and may be extremely so. The most common site of aphthæ is the mucous membrane of the lips and mouth, but they occasionally appear wherever mucous membrane approaches the skin.
Infants are liable to an aphthous eruption termed Thrush (q.v.). Aphthæ in adults are generally a consequence of fevers and other diseases, or a symptom of disturbance of the digestive system. In some cases of pulmonary consumption, they form a painful addition to the patient's sufferings. In ordinary cases of aphthæ, a preparation of borax, or some antiseptic wash, generally effects a rapid cure. Where the pain is severe, a simple application of solid nitrate of silver is the best remedy.