August Krogh Danish physiologist, awarded the Nobel Prize in Physiology or Medicine in 1920 Date of Birth: 15.11.1874 Country: Denmark

Biography of August Krogh

August Krogh was a Danish physiologist who was awarded the Nobel Prize in Physiology or Medicine in 1920. He was born in Grenaa, Denmark, in a family of shipbuilders, brewers, and newspaper publishers. From a young age, Krogh developed an interest in natural sciences and spent a lot of time studying insects in the surroundings of his home.

At the age of 14, Krogh left school and joined the Danish naval ship guarding the fishing grounds of Iceland, dreaming of becoming a naval officer. This service instilled in him a lifelong love for the sea and ships. After a year, he resumed his studies at the cathedral school in Aarhus, and in 1893, he enrolled in the University of Copenhagen to study physics and medicine.

Under the influence of zoologist William Sorensen, Krogh began studying the larvae of the Corethra organism living in water. He discovered that their swim bladder functions similar to a diving submarine. Krogh's interests were further influenced by lectures by Christian Bohr, the father of physicist Niels Bohr, who was an authority in the field of blood and respiration physiology. In 1897, Krogh started working under Bohr's guidance at the laboratory of medical physiology. Two years later, Krogh obtained a master's degree in zoology from the University of Copenhagen and was appointed as Bohr's assistant.

To conduct his research on Corethra, Krogh invented the microtonometer, a device for measuring the partial pressure or tension of gas dissolved in a liquid, such as oxygen in blood. In 1902, during a marine expedition to Greenland, Krogh measured the oxygen and carbon dioxide content in seawater and freshwater and improved the method of tonometric measurement of dissolved gases. This work provided new insights into the role of the ocean in regulating atmospheric carbon dioxide levels.

In the following year, Krogh received a doctorate in zoology from the University of Copenhagen for his dissertation on the pulmonary and cutaneous respiration of frogs. He discovered that cutaneous respiration in frogs is relatively constant, while pulmonary respiration varies and is regulated by the vagus nerves associated with the autonomic nervous system. During respiration, oxygen passes through the lung capillaries via the alveoli membranes. Oxygen is then distributed to the body tissues and, through oxidation, is converted into carbon dioxide. In turn, carbon dioxide passes from the blood to the alveoli and is expelled from the body by the lungs. At the time of Krogh's research, the mechanism of respiration was still unclear, and there was a debate between two opposing concepts. According to one concept, the alveolar-capillary cell actively secretes respiratory gases in one direction or another. Supporters of the opposing view claimed that gases diffuse passively through this membrane. Bohr, who believed that the lungs functioned like glands, adhered to the first concept. However, using the microtonometer, which allowed the measurement of oxygen and carbon dioxide partial pressures in the lungs and blood, Krogh and his colleagues proved that gas exchange in the lungs occurs only through diffusion. Additionally, Krogh and Bohr described the influence of different concentrations of carbon dioxide on the oxygen-hemoglobin dissociation curve of blood, known as the Bohr effect.

In 1905, Krogh married Marie Jorgensen, who also worked as a physiologist in Bohr's laboratory. Their son became a prosector in the anatomy department at the University of Aarhus, their two daughters became dentists, and their youngest daughter became a physiologist in the United States. A year after his marriage, Krogh was awarded the Sigmund Sigmundsson Prize from the Austrian Academy of Sciences for his work demonstrating that gaseous nitrogen does not participate in normal metabolic processes in animals. His international recognition grew further when he presented his work on gas diffusion in the lungs at the International Congress of Physiologists in Heidelberg, Germany, in 1907.

In 1908, a position of adjunct professor of zoology was established specifically for Krogh at the University of Copenhagen. In the same year, he and his wife embarked on a second expedition to Greenland to study the effects of a diet consisting almost exclusively of meat on metabolism and respiration in Eskimos. Two years later, the University of Copenhagen provided Krogh with a physiological laboratory in Ny Vestergade, where the couple continued their collaboration. Together with Johannes Lindgaard, who later became a professor of gymnastics theory, Krogh determined the minute volume of the heart at rest and during muscle exertion using the method to measure the rate of blood flow in the lungs with nitrous oxide. The researchers found that the amount of arterial blood leaving the left heart chambers depends on the amount of venous blood flowing into the right chambers.

In 1916, Krogh was appointed as a professor of zoology at the University of Copenhagen. In a series of studies, he investigated the physiological regulation of capillary blood flow, which determines the delivery of oxygen to tissues and cells. Capillaries are tiny blood vessels with diameters of a few microns, consisting of a single layer of cells. They facilitate the exchange of oxygen, carbon dioxide, nutrients, and other substances between the blood and tissues. Previous studies on muscle capillaries under a binocular microscope had shown that capillaries "open" and "close" asynchronously, meaning they do not follow the rhythm of arterial pressure oscillations. It was also known that any increase in blood flow due to increased arterial pressure leads to an increase in capillary blood flow. Based on the observation that the surface area of "open" or functioning capillaries (capillary diffusion surface) must directly depend on the consumption of oxygen, Krogh demonstrated that the number of functioning capillaries, in turn, is regulated by local mechanical, chemical, and temperature factors. In experiments conducted on frog tongues, he found that the capillaries are visible and filled with blood during tongue muscle activity but empty and invisible at rest. Later, one of Krogh's students, Bjørn Wimtrup, reported that the "opening" and "closing" of capillaries are controlled by contractile elements in specialized cells of the capillary wall called Rouget cells. Krogh's research on lung gas exchange and capillary blood flow regulation laid the foundation for the use of intubation during anesthesia and the application of hypothermia in open-heart surgeries.

In 1920, Krogh was awarded the Nobel Prize in Physiology or Medicine for his discovery of the mechanism of capillary regulation. He demonstrated that only a portion of capillaries is open at rest, while their number increases during activity in accordance with oxygen consumption. Krogh's proof that this mechanism operates in all organs and tissues has significant implications for modern science. In his Nobel lecture, Krogh discussed the physiology of capillaries based on data obtained from frog experiments.

During his trip to the United States in 1922 to deliver the Silliman lectures at Yale University, Krogh studied insulin, which had been discovered a year earlier by Frederick G. Banting and John D.R. Macleod. Due to his wife's diabetes, insulin held a particular interest for Krogh, and he made substantial contributions to establishing laboratories in Denmark for the study and production of insulin. Furthermore, Krogh investigated the permeability of cell membranes to water and salts, differences in respiration during flight in various insects, and the history of scientific development. He had a keen interest in the sociobiology of bees and wrote articles discussing the work of Karl von Frisch on the development of communicative links in honeybees.

When the fascist army occupied Denmark, Krogh, a staunch opponent of Nazism, moved to Sweden. Upon his return to Denmark in 1945, he resumed his work at his department in the University of Copenhagen and continued his research in the laboratory provided by the Carlsberg and Scandinavian Insulin Foundations. Krogh wrote numerous popular science books and was an avid book lover himself, particularly enjoying the novels of Rudyard Kipling. Krogh passed away in Copenhagen on September 13, 1949.

English physiologist Archibald V. Hill wrote about Krogh, "Krogh was an excellent experimenter and an inventive maker of scientific instruments, but his experience and love for beautiful methods never overshadowed fundamental scientific problems."

Krogh received numerous awards, including the Bailey Medal from the Royal Society of Medicine in London (1945), honorary degrees from the University of Edinburgh, Budapest, Göttingen, Harvard, Rutgers, Oxford, Lund, and Oslo, and honorary memberships in the London Royal Society and many other scientific societies.