I swear by Apollo [the Greek god of the sun and of medicine] . . . and all the gods and goddesses . . . that I will fulfill . . . this oath. . . . I will apply . . . measures for the benefit of the sick according to my ability and judgment; I will keep them from harm and injustice.

DOCTORS OFTEN SPEAK these solemn words, part of a pledge called the Hippocratic oath, when they graduate from medical school. The oath is credited to a Greek physician named Hippocrates, who lived in the fourth century B . C . Even though it was written long ago, many physicians still consider the Hippocratic oath a basic statement of the medical profession's ethics and duties. Chief among these is "do no harm." The oath goes on to name one particular form of harm that a doctor must promise not to do: "I will neither give a...