August and Marie Krogh

by Bodil Schmidt-Nielsen

August Krogh, the son of a brewer, studied zoology in Copenhagen and earned his doctoral degree under the physiologist Christian Bohr, the father of the world-renowned nuclear physicist Niels Bohr. Krogh's unusual ability to construct instruments and complex apparatuses and his intuitive understanding of physical principles made it possible for him to improve on Bohr's methods. His findings led him to challenge Christian Bohr's ideas about oxygen secretion, and when Bohr refused to accept his findings, Krogh unwillingly came into a painful conflict with his own mentor. Krogh's continued studies of how oxygen is supplied to the tissues led to his realization that the blood flow in the finest blood vessels, the capillaries, has to be regulated through a mechanism that opens and closes the capillaries according to the tissue's need for oxygen. This idea and his scientific proof were at the time so new and revolutionary that he was promptly (in 1920) awarded the Nobel Prize. His fame in De