Merck Manual of Diagnosis and Therapy. The Merck Manual’s 17th, Centennial Edition is available free, searchable by keyword or the table of contents. Merck also offers two other complete manuals through this site: The Merck Manual of Geriatrics and The Merck Manual of Health & Aging.Access:http://www.merck.com/mrkshared/mmanual/sections.jsp.