David A. Shaywitz is an MD/PhD student at Harvard Medical School and MIT. Martin A. Samuels is professor of neurology at Harvard Medical School and chairman of the Department of Neurology at the Brigham and Women's Hospital.

If you have a blood clot in your leg, and your doctor tells you not to worry, you just may want to ask about Uncle Marvin.

There are few relationships traditionally more sacred than that between patient and physician. As a patient, you expect both an empathetic ear and a compassionate heart. As a physician, you have sworn an oath, declaring allegiance to a tradition that for more than two millennia has pledged to act always "for the benefit of my patients . . . for the benefit of the sick."