Frank, Otto (1865–1944), German physiologist. Frank served as a professor at several German universities, his longest tenure being at Munich. He pioneered in the development of exact physiological recording techniques. In 1904 he published the first study of direct monitoring of heart sounds. He devised a great number of recording instruments. He published the fruits of his research in a handbook of physiological methodology. Areas of his research included the origin of the arterial pulse, a determination of the volume of blood in the heart, and the functioning of the aorta. Frank also made original contributions to the physiology of the ear.
Starling, Ernest Henry (1866–1927), British physiologist. Starling was one of the outstanding physiologists of his time. He served for many years as professor of physiology at University College in London. His foremost contributions to physiology include an understanding of the maintenance of fluid balance in body tissues, the regulatory role of endocrine secretions, and mechanical controls on heart function. Much of his work was in collaboration with the physiologist William Bayliss (1860–1924). In 1902 they isolated a substance that is released into the blood from the epithelial cells of the duodenum, which in turn stimulates secretion into the intestine of pancreatic digestive juice. Two years later Starling coined the term hormone as the name for such substances. In 1918 he formulated a law concerning the heart, stating that (other conditions being equal) the greater the filling of the heart during diastole, the greater the following systole. Thus the heart is able to maintain a constant beat despite considerable variations in blood flow. This law of the heart led to the concept upon which the law of muscle contraction is based.