Ernest Starling (1866-1927) was pre-eminent in the golden age of British Physiology. His name is usually associated with his "Law of the Heart," but his discovery of secretin (the first hormone whose mode of action was explained) and his work on capillaries were more important contributions. He coined the word 'hormone' one hundred years ago. His analysis of capillary function demonstrated that equal and opposite forces move across the capillary wall—an outward (hydrostatic) force and an inward (osmotic) force derived from plasma proteins.