August Krogh (pronounced Krawg) won the 1920 Nobel Prize for physiology or medicine for the discoveries he made concerning human respiration. Krogh showed that most capillaries (the smallest blood vessels) of the body's organs and tissues are closed when they are at rest, but when there is activity and the need for oxygen increases, more capillaries will open. Krogh's explanations of respiration and capillary action were of major significance for the understanding of the physiology of the human pulmonary and circulatory systems. His research into respiration and circulation also had practical applications for the development of modern medical science.

Schack August Steenberg Krogh was born in Grenaa, Jutland. His father was a brewer, shipbuilder, and a newspaper editor. His mother, Marie Drechmann Krogh, was of gypsy ancestry. Throughout his life Krogh was active in both zoology and human physiology, accomplishing his major discoveries in the physiology of respiration. In...