Schack August Steenberg Krogh ForMemRS (15 November 1874 – 13 September 1949) was a Danish professor who worked at the University of Copenhagen from 1916 to 1945. He taught in the department of zoophysiology, which studies how animals function. Krogh made important discoveries in the field of physiology and is known for creating Krogh's principle.

In 1920, August Krogh received the Nobel Prize in Physiology or Medicine for discovering how blood flow is controlled in muscle tissue. He was the first person to explain how blood supply to muscles and other organs changes based on need by opening or closing tiny blood vessels called arterioles and capillaries.

In addition to his work in medicine, Krogh helped start a company that is now called Novo Nordisk.

Life

He was born in Grenaa on the peninsula of Djursland in Denmark, the son of Viggo Krogh, a shipbuilder. His mother (born Drechmann) was the daughter of a customs officer in Holstein. Through his mother’s family, he claimed "a dash of" Romani blood [2]. Krogh was educated at the Aarhus Katedralskole in Aarhus. He attended the University of Copenhagen, earning a Master’s degree in 1899 and a Doctor of Philosophy degree in 1903.

Krogh was a leader in the study of comparative physiology. He wrote his thesis on how frogs breathe through their skin and lungs, titled Respiratory Exchange of Animals, published in 1915. Later, Krogh studied how aquatic animals maintain balance in water and electrolytes, publishing books titled Osmotic Regulation (1939) and Comparative Physiology of Respiratory Mechanisms (1941). He wrote over 200 research articles for international journals. He also designed scientific tools, including the spirometer and the device for measuring basal metabolic rate, which were widely used.

Krogh began teaching at the University of Copenhagen in 1908 and became a full professor in 1916. He led the first laboratory for animal physiology (zoophysiology) at the university.

Krogh was elected an International Honorary Member of the American Academy of Arts and Sciences in 1931, an International Member of the United States National Academy of Sciences in 1937, and an International Member of the American Philosophical Society in 1941.

In the 1930s, Krogh worked with two other Nobel Prize winners, the radiochemist George de Hevesy and the physicist Niels Bohr, to study how membranes allow heavy water and radioactive isotopes to pass through. Together, they helped Denmark obtain its first cyclotron, which was used for experiments on animal and plant physiology, as well as in dental and medical work.

Foundation of Novo Nordisk

In 1922, August Krogh traveled to North America on a lecture tour after winning the Nobel Prize in Physiology or Medicine. During this trip, he and his wife Marie, a doctor who had type 2 diabetes, visited Toronto. There, scientists Frederick Banting, Charles Best, and John Macleod had recently created usable insulin. Krogh was allowed to make insulin in the Nordic countries and worked with Hans Christian Hagedorn, a doctor who specialized in diabetes, to begin producing insulin in Denmark. This effort led to the founding of Nordisk Insulinlaboratorium company in 1923.

In 1925, brothers Harald and Thorvald Pedersen, former workers at Nordisk, started their own company called Novo Terapeutisk Laboratorium. Novo and Nordisk competed until they joined together in 1989 to form Novo Nordisk A/S.

Family

In 1905, he married Marie Krogh (born Jørgensen, 1874–1943). She was a well-known scientist, and much of August Krogh's work was done together with her. August and Marie had four children. Their youngest child, Bodil, was born in 1918. Bodil also became a physiologist and was the first woman to serve as president of the American Physiological Society in 1975. Bodil married Knut Schmidt-Nielsen, who was also a well-known physiologist.

Legacy

Torkel Weis-Fogh, an important researcher who studied how insects fly, was a student of August Krogh. Together, they wrote a well-known paper on insect flight in 1951.

Two things are named after Krogh:
• Krogh length, which is the distance between tiny blood vessels where nutrients move to cells, based on how much the cells use the nutrients.
• Krogh’s principle, which states that "for many problems, there is an animal that is best to study, or a few such animals."

In his book, The Anatomy and Physiology of Capillaries, Krogh shared a mistaken idea that if all the blood vessels in a human body were laid out, they would stretch 100,000 kilometers. This number was based on incorrect assumptions about how dense blood vessels are in the body. Krogh also used a hypothetical body that weighed 140 kilograms, with 50 kilograms of pure muscle, which is not a realistic body type. Recent research suggests the actual total length of blood vessels in the human body is between 9,000 and 19,000 kilometers.

Publications

• How Animals and Humans Breathe and Exchange Gases (1916)
• How Aquatic Animals Control Water Balance (1939)
• Comparing How Different Animals Breathe (1941)