text Alexandria,VA U.S. Patent and Trademark Office [1970]- monographic Title from home page last updated Apr. 10, 2006 (viewed Apr. 21,2006). United States Patent and Trademark Office. Patents C 21.31/17-2: C 21.31/17-2: http://purl.access.gpo.gov/GPO/LPS19940 http://purl.access.gpo.gov/GPO/LPS19940 20160527183600.0 299327