August Krogh (1874-1949), Danish physiologist. A pioneer in comparative studies on animals, Krogh made several fundamental discoveries concerning the regulation of blood flow, for which he won the Nobel Prize in Physiology or Medicine in 1920. Working at the University of Copenhagen, he discovered capillaries could open and close to regulate blood perfusion in the muscles. He was also responsible for developing physiological measuring apparatus still in use today, such as the recording spirometer, bicycle ergonometer and precision pipettes. This portrait is from the Bain News Service, one of America's oldest news picture agencies, which holds images dating from the 1890s to the 1930s.