For the purpose of making an issue, or of opening a large collection of matter, such as a chronic or "cold" abscess, caustic potash was formerly often, and for the latter purpose is still occasionally, used. Macnamara has found better results from it than from the knife in opening bubo (Ranking, i., 1872), and others recommend it in carbuncle. It causes pain but no hemorrhage, and makes a good free opening for the escape of the slough.