Schack August Steenberg Krogh, a Danish physiologist who greatly expanded our understanding of the circulatory system, was born on this day in 1874.
Krogh spent almost his entire career at the University of Copenhagen. First he studied respiration; his treatise Mechanism of Gas Exchange in Lungs netted him a prize in 1906 from the Vienna Academy of Science. Greater honors would soon follow. After shifting his attention to the circulatory system, Krogh observed that active muscles have more open capillaries than do less active ones, and that capillaries contract or dilate in proportion to a tissue's oxygen needs. For these famous animal studies, he received the Nobel Prize for Physiology or Medicine in 1920.
Krogh retired from the university in 1945. He died in 1949.
[Source: Britannica Online]