The Danish physiologist Schack August Steenberg Krogh (1874-1949) is noted for his classic researches on the anatomy and physiology of the blood capillaries and his contributions to respiratory physiology, marine biology, and cell physiology.

August Krogh was born on Nov. 15, 1874, in Grenaa, Jutland. As a boy, he read widely in botany, zoology, physics, and chemistry, but he was uncertain at first whether to specialize in physics or zoology. He attended lectures on medical physiology by Christian Bohr, father of the physicist Niels Bohr, and decided forthwith to follow a career in physiology. In 1899 Krogh was appointed assistant in Christian Bohr's laboratory, and in 1903 he received a doctorate for his analysis of respiratory exchanges of oxygen and carbon dioxide in the lung and skin of frogs.

With his own new methods Krogh extended his studies of respiration to other animals, including man. At the time he started research, it was thought that the lung secreted oxygen into the bloodstream. In 1910, when his famous seven papers on the mechanism of gas exchange appeared, Krogh could state beyond doubt, "The absorption of oxygen and elimination of carbon dioxide in the lungs takes place by diffusion and by diffusion alone." In 1908 he was made head of his own Zoophysiological Laboratory, first as dozent and then in 1916 as professor of zoophysiology in the University of Copenhagen. This laboratory and a still larger one, built in 1926 for him and to his own detailed specifications, became world-famous research centers, attracting students from far and near.

Beginning in 1915, Krogh turned his attention to the mechanisms by which blood capillaries supply oxygen to muscle cells and remove carbon dioxide in the large volumes demanded by exercise. His hypothesis of metabolically controlled, intermittent opening of capillary blood vessels led to experiments for which he received the Nobel Prize in 1920 and to a monograph entitled The Anatomy and Physiology of the Capillaries. This book still has unprecedented influence on medical research because of its implications for cell metabolism, water balance, inflammation, and disease.

Throughout his life Krogh maintained a knowledge of physics and physical chemistry rarely attained by biologists of the time. He also had a brilliant, intuitive perception of physical conditions, especially in microscopic dimensions. His ingenuity extended to the development of quantitative micromethods and inexpensive apparatus especially suited to each research project. Between other studies he returned repeatedly to earlier interests in marine biology, insect physiology, and osmotic relationships in plants and animals. As soon as isotopes became available, he studied diffusion and ion-pump mechanisms across membranes of single cells. Retirement from the university in 1945 meant merely the transfer of research and writing to his home laboratory.

After a brief illness August Krogh died on Sept. 13, 1949. The versatility and originality of his contributions to the life sciences, together with his scores of devoted students, place Krogh among the topmost few who produced the unprecedented growth of biology, physiology, and scientific medicine during the first half of the 20th century.

Further Reading

• A 30-page memoir by P. Brandt Rehberg serves as a preface to the 1959 reprint of Krogh's The Anatomy and Physiology of the Capillaries. That volume also contains Krogh's last published paper, "Reminiscences of Work on Capillary Circulation," a lecture given in 1946 at Harvard Medical School.
• Schmidt-Nielsen, Bodil, August and Marie Krogh: lives in science, New York: American Physiological Society, 1995.