ScienceScope ScienceScope Science 25 Oct 1991:Vol. 254, Issue 5031, pp. 507DOI: 10.1126/science.1948019 Article Info & Metrics eLetters PDF This is a PDF-only article. The first page of the PDF of this article appears above.
Science Vol 254, Issue 503125 October 1991 Table of Contents Print Table of Contents Back Matter (PDF) Ed Board (PDF) Front Matter (PDF)
