August Krogh

Schack August Steenberg Krogh was born on 15 November 1874 and spent three decades at the University of Copenhagen's zoophysiology department, holding a professorship from 1916 to 1945. His research cut across multiple fields, but the breakthrough came when he described how capillaries in skeletal muscle regulate themselves: opening when tissue demands oxygen, closing when it doesn't, with arterioles controlling the gates. The Nobel committee recognized the discovery in 1920. He also articulated what became known as Krogh's principle, a guide for choosing the right animal model to study a physiological problem. Outside the lab, he co-founded the company that grew into Novo Nordisk. He died on 13 September 1949.