NOTICE: The project that is the subject of this report was approved by the Institute of Medicine's Council.

This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.

The Institute of Medicine was chartered in 1970 by the National Academy of Sciences to enlist distinguished members of the appropriate professions in the examination of policy matters pertaining to the health of the public. In this, the Institute acts under both the Academy's 1863 congressional charter responsibility to be an adviser to the federal government and its own initiative in identifying issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.

The Institute gratefully acknowledges the generous support of the following organizations toward its 25th anniversary activities: Albert Einstein College of Medicine of Yeshiva University, the Carnegie Corporation of New York, the Commonwealth Fund, Kaiser-Permanente, Memorial Sloan-Kettering Cancer Center, New York Hospital, the University of Rochester Medical Center, and Yale University School of Medicine; corporate benefactor—Bristol-Myers Squibb; corporate patron—Pfizer, Inc.; and corporate sponsors—Amgen, Inc., Eli Lilly and Company, Procter and Gamble, G.D. Searle and Company, Sandoz Pharmaceuticals Corporation, Schering-Plough Corporation, and the Upjohn Company.

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The serpent has been a symbol of long life, healing, and knowledge among almost all cultures and religions since the beginning of recorded history. The serpent adopted as a logotype by the Institute of Medicine is a relief carving from ancient Greece, now held by the Staatlichemuseen in Berlin.