William Henry Howell (1860-1945), American physiologist. Howell was appointed the first professor of physiology at Johns Hopkins Medical School, Baltimore, USA in 1893. He studied the circulatory system, and the importnace of inorganic salts in the maintenance of heart rate. Following studies on the mechanism of blood clotting and the isolation of clotting protein thrombin, he isolated a powerful anticoagulant, named heparin because of its high concentration in the liver. He also wrote a Textbook of Physiology (1905) which was a standard text for medical students and went through 14 editions in Howell's lifetime.