NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This project was funded by the U.S. Department of Health and Human Services, Health Care Financing Administration Contract No. 500-98-0275. Any opinion, findings, conclusions, or recommendations expressed in this publication are those of the Institute of Medicine committee and do not necessarily reflect the view of the funding organization.

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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 image adopted as a logotype by the Institute of Medicine is based on a relief carving from ancient Greece, now held by the Staatliche Museen in Berlin.