The Greco-Roman physician Galen advocated the bleeding of patients with leeches, a practice that persisted in various parts of the world for many centuries. Throughout most of Western history, leeching—or leechcraft—became such a common practice that a physician was commonly referred to as a “leech.”
Bassanio rejects the gold casket because he is aware that European moral iconographies repudiate earthly wealth (though, ironically, Bassanio is a poor illustration of the principle).
