By Kevin T. Patton, PhD, Professor of Anatomy & Physiology Instruction, New York Chiropractic College, Seneca Falls, New York; Professor Emeritus of Life Sciences, St. Charles Community College, Cottleville, Missouri; Assistant Professor Emeritus of Physiology, Course Director Emeritus in Human Physiology, St. Louis University Medical School, St. Louis, Missouri, USA and Gary A. Thibodeau, PhD, Chancellor Emeritus and Professor Emeritus of Biology, University of Wisconsin, River Falls, River Falls, Wisconsin, USA