In ceremonies across the country this week, robed medical school graduates will rise, degrees in hand, and perform their first act as physicians and their last as students.

They will swear an oath with ties to ancient times, one generally credited to Hippocrates.

The ritual is an eerie chant of principles that Dr. William Henrich, the University of Maryland's chairman of internal medicine, describes as a resonating link with all physicians: those long since gone, the robed young doctors standing shoulder to shoulder in the ceremonies of the present, the healers yet to come.

But what it will not be, in almost every instance, is the original oath the Greek physician ordained - if, indeed, he ever did.

"It's a wonderful tradition," said Dr. Howard Markel, a University of Michigan medical historian who has written an article on the oath in the current issue of the New England Journal of Medicine. But "very few people from different schools swear to the same oath."

Hippocrates was widely believed to have lived between 460 and 380 B.C. But the oath attributed to him is probably a compilation, perhaps cobbled together from the notes of his students and rewritten by others, Markel said. The National Library of Medicine posits on its Web site that the oath was more strongly influenced by followers of Pythagoras - the Greek philosopher, mathematician and supposed vegetarian health nut - than Hippocrates.

Whatever its origin, there's no question that today's versions are often the product of rewritings, including by modern-day medical students. Gone are the genuflections to Greek gods such as Apollo, the requirement to hold medical professors as dear as one's parents and - because today's students, doctors and ethicists couldn't come to a consensus - its prohibitions against euthanasia and abortion.

But most of the pledges still call on doctors to put patients first, protect confidentiality and, at the least, avoid criminal medical acts. Many call on them to go much further, conducting themselves with honor in all things and holding themselves "aloof from wrong."...

Despite its ancient roots, the pervasive saying of oaths at medical schools is actually a fairly recent phenomenon, Markel writes. His article notes that the first recorded administration of the Hippocratic Oath in a medical school setting appears to have taken place at the University of Wittenberg in Germany in 1508, though it didn't become a standard part of medical school graduation ceremonies until 1804 in Montpellier, France.

Gradual acceptance

A survey published in a 1928 bulletin of the Association of American Medical Colleges found that about 19 percent of the 74 responding medical schools in North America included the oath in commencement exercises.

After World War II atrocities sparked a focus on medical ethics, a 1958 survey found that 74 percent of U.S. medical schools and 58 percent in Canada administered professional oaths, said Dr. Edward Halperin, a Duke University vice dean. By 1982, he wrote in a 1989 review, 94 percent of U.S. medical schools and 63 percent in Canada administered oaths.