Headache:Diagnosis and Treatment, edited by C. David Tollison, Ph.D. and Robert S. Kunkel, M.D. Baltimore, MD: Williams and Wilkins, 1993, 418 pp., $85.00.The Prevention of Postoperative Pain: Proceedings of a Symposium on the Prevention and Control of Postoperative Pain, edited by Harold Merskey and Ken Prkachin. Halifax, Nova Scotia: The Canadian Pain Society, 1993, 86 pp., $10.00 (Cdn.).