This volume contains the proceedings of the fifth annual symposium held October 1971 at the Texas Research Institute of Mental Sciences in Houston. We are grateful to Curtin Scientific Company, Fisher Scientific Company, Geigy Pharmaceuticals, The Gerontological Society, ICN Bentex Pharmaceutical Company, Ives Laboratories, Knoll Pharmaceutical Company, Merck Sharp & Dohme Postgraduate Program, The Moody Foundation, The Pauline Sterne Wolff Memorial Home, Pfizer Laboratories, Roche Laboratories, Sandoz Pharmaceuticals, Schering Corporation, and E.R. Squibb & Sons for their generous financial...