Skip to main content
Select Source:

Krogh, Schack August Steenberg

Krogh, Schack August Steenberg

(b. Grenå, Jutland, Denmark, 15 November 1874; d. Copenhagen, Denmark, 13 September 1949)

Zoology, physiology.

His family had lived for 300 years in southern Jutland, and Krogh never lost his affection for this area. His father, a brewer who had been educated as a naval architect, inspired his son’s love of ships and the sea.

In 1893 Krogh graduated from the Århus cathedral school—in 1889 he had tried a voluntary apprenticeship in the Royal Navy to become an officer—and entered the University of Copenhagen as a medical student. But a friend of the family, the zoologist William Sørensen, inspired Krogh to study zoology and recommended that he attend the physiology lectures of Christian Bohr. After obtaining his M.Sc. degree in 1899, Krogh became an assistant to Bohr in hsi laboratory. In 1905 he married Marie Jørgensen, a physician. They had three daughters and one son.

In 1896 Krogh had begun studying the hydrostatic mechanism of the air bladders in Corethra larvae. He demonstrated that these organs “function like the diving tanks of a submarine.” For his studies Krogh used a microscopic method of analysis on air in minimal bubbles. During these years he also published critical works on physical properties in biology, topics rather uncommon at that time. All his life Krogh was more interested in physical than in chemical problems in biology, and he explained his critical attitude thus:

When experimental results are found to be in conflict with those of an earlier investigator, the matter is often taken too easily and disposed of for an stance by pointing out a possible source of error in the experiments of the predecessor, but without inquiring whether the error, if present, would be quantitatively sufficient to explain the discrepancy. I think that disagreement with former results should never be taken easily, but every effort should be made to find a true explanation. This can be done in many more cases than it actually is; and as a result, it can be done more easily than anybody else by the man “on the spot” who is already familiar with essential details. But it may require a great deal of imagination, and very often it will require supplementary experiments [“August Krogh,” in Festkrift Københavns Universitet 1950 (Copenhagen, 1950), p. 185].

In 1903, at the University of Copenhagen, Krogh defended a thesis on the cutaneous and pulmonary respiration of the frog, which was a synthesis of Bohr’s work in respiratory physiology and his own in zoology. Krogh demonstrated that the exchange of oxygen takes place essentially through the thin pulmonary walls, with their short diffusion path, while the more diffusible carbon dioxide is expired through the skin. The study showed his abilities for quantitative and very accurate work and for “visual thinking,” which enabled him to foresee and construct his often simple experimental tools without drawing them beforehand. This showed up especially in the first of his works to gain international fame, his paper on the pulmonary exchange of nitrogen, for which he was awarded the Seegen Prize of the Vienna Academy of Sciences. Through a new, very accurate temperature-control apparatus, he was able to demonstrate that free nitrogen takes no part in respiratory exchanges.

During his first years with Bohr, Krogh believed that pulmonary air exchanges took place mainly through secretory processes regulated by the nervous system. Since the great problem concerning passive or active moments for pulmonary exchange could not be solved with his instruments, Krogh invented a tonometer and a device for microanalysis of gases. Only 10cu. mm. was necessary for the microtonometer to obtain equilibrium between the tension of air in blood and in the bubble, and dissolved gases in the pulmonary alveoli and in the bubble could be contrasted with sufficient accuracy.

Through his investigations Krogh concluded that the pulmonary gas exchange depended on diffusion; in 1904 he published with Bohr and K. A. Hasselbalch a study on the relation between the carbon dioxide tension and the oxygen association of blood. In 1910 he published his seven famous articles on the mechanism of gas exchange, prepared in collaboration with his wife. Krogh wrote:

I shall be obliged in the following pages to combat the views of my teacher Prof. Bohr on certain essential points and also to criticize a few of his experimental results. I wish here not only to acknowledge the debt of gratitude which I personally owe to him, but also to emphasize the fact, obvious to everybody familiar with the problems here discussed, that the real progress made during the last twenty years in the knowledge of the processes in the lungs is mainly due to his labors and to that refinement of methods which he has introduced. The theory of the lung as a gland has justified its existence and done excellent service in bringing forward facts, which shall survive any theoretical construction that has been or may hereafter be put upon them [“The Mechanism of Gas Exchange” (1910), p. 257].

Krogh summed up his results as follows: “The absorption of oxygen and the elimination of carbon dioxide in the lungs take place by diffusion and by diffusion alone. There is no trustworthy evidence of any regulation of this process on the part of the organism.” Against criticism from followers of the secretion theory, Krogh’s further investigations confirmed that the partial tension of oxygen was always greater in the alveolar air than in the blood, so that conditions for diffusion had to be equal.

This new point of view created several other problems, and during the following years Krogh published works concerning the blood flow through the lungs and the influence of the venous supply upon the output of the heart. With Johannes Lindhard, later professor of gymnastic theory, he took up the topics of dead space, respiration and muscle work, and variations in the composition of alveolar air. His wife, a physician, inspired him. In 1913 they published a study of the diet and metabolism of the Eskimo, a result of travels in 1902 and 1908 to Greenland. Krogh’s work on the tension of carbonic acid in natural waters was a result of the Greenland journey.

In 1908 a special associate professorship of zoo-physiology was created for Krogh at the University of Copenhagen, and he left Bohr’s laboratory even without the prospect of a laboratory for himself. In 1910, however, he acquired a laboratory in Ny Vestergade, which originally had been used by the bacteriologist Salomonsen. It was simply equipped, so Krogh set up a laboratory in his official residence and lived in the small rooms of the top story. Here he developed his many instruments for evaluating the function of blood flow and respiration: the rocker spirometer, the electromagnetic bicycle ergometer, and a gas analysis apparatus accurate to 0.001 percent. He demonstrated the influence of fat and carbohydrate as sources of muscle energy and found the oxygen deficit created through muscle work. With Lindhard he worked out the nitrous oxide method for determination of the heart’s volume per minute.

From these studies Krogh early concluded that the capillaries of the muscles were partially closed during rest and, for the most part, open during work; using intensive microscopical and histological methods, he was able to demonstrate the truth of his ideas and in 1920 was awarded the Nobel Prize in physiology or medicine. Several others had conducted capillary investigations before Krogh, but none had addressed the problem specifically nor understood its significance for the entire circulation.

During these years many foreign scientists flocked to Krogh’s laboratory: Goeran Liljestrand (Sweden), Joseph Barcroft and Thomas Lewis (England), and Edward Churchill, Cecil Drinker, Eugene Landis, Alfred N. Richards, and A. H. Turner (United States). Among the problems studied was the evaluation of hormonal, chemical, and nervous regulation of the capillaries. The Danish physician Bjovolf Vimtrup, who worked with Krogh, demonstrated in a doctoral thesis, “Über contractile Elemente in der Gefässwand der Blutcapillaren” (Copenhagen, 1922), that Rouget cells constricted frog capillaries. Later investigations have confirmed the appearance of an epithelial mechanism in mammals.

With his co-workers Krogh now demonstrated that capillary movements were influenced by both nerves and hormones, and in 1922 he published his monograph on the anatomy and physiology of capillaries. In 1916 he had written on respiratory exchange in animals and man, but this was mainly a reference book. It opened the way for tracheal insufflation in medicine and paved the way for the use of hypothermia in heart surgery through its demonstration of the slowing down of gaseous exchange at low temperatures. His later monograph, on the other hand, reads like an exciting novel; it reached five editions and was translated into German in two editions (Krogh wrote perfect English).

After 1920 Krogh worked with problems concerning edema and stasis, and during a lecture trip to the United States in 1922 he was able to study the newly discovered insulin; his wife had diabetes mellitus. On his return to Denmark, he and the internist H. C. Hagedorn organized the fabrication of Danish insulin and sold it privately without profit. Two famous institutions, Nordisk Insulinlaboratorium and Nordisk Insulinfond, were established largely through the efforts of these two foresighted men. With A. M. Hemmingsen, Krogh worked on the standardization of insulin.

Two years later the Rockefeller Foundation offered to provide better working facilities for Krogh, and a new institution with room for five other university laboratories was erected in Juliane Mariesvej; Krogh worked out plans for every room (even considering the shadows cast by the trees surrounding the building). In 1928 the institute, named the Rockefeller Institute, was officially opened. Krogh had tried to obtain special dustless rooms, but the building materials at that time made it impossible. During the first years of the institute, he continued his studies on heavy muscle work. He created new methods for determination of total osmotic tension of blood and studied the balance of insensible perspiration. Krogh also became interested in the physiological problems of heating houses. As chairman of a committee of the Academy for the Technical Sciences, he eagerly took part in the planning of technical and physiological investigations; and his microclimatograph proved to have many applications. He worked in this area until his death.

Besides his physiological studies of vertebrates, Krogh never lost his interest in zoophysiology. He started with the investigations of the Corethra larvae, and with his microanalysis apparatus for measuring air tensions in blood he demonstrated the essential importance of diffusion for insect respiration. Later, with his microrespirometer apparatus, he showed the influence of temperature on the metabolism of insects; in this way he also established that metabolism, even in other animals, follows van’t Hoff’s theorem. Between these studies he carried out investigations with J. Leitch on the oxygenation of fishes and with H. O. Schmit-Jensen on the fermentation of cellulose.

Another question which interested Krogh was the metabolism of sea animals: whether these creatures could live on dissolved material. With the zoologist R. Spärck he studied plankton and dissolved substances as food for aquatic organisms, as well as the aforementioned investigations on the relationship of carbon dioxide in air and seawater. Refuting the theories of A. Pütter, Krogh turned his attention to the exchange of water and inorganic ions through the surfaces of living cells and membranes, utilizing isotopes as indicators. He continued his osmoregulatory investigations and in 1939 set forth his ideas in a monograph—like the book on capillaries, a classic. One year later he published his fascinating and lucid monograph on respiratory mechanisms, with up-to-date knowledge of comparative physiology.

During his last years—after his retirement in 1945 as ordinary professor, a chair which had been created for him in 1916—Krogh took up a problem from his youth: the flight of insects and birds. In his private laboratory in Gentofte, with T. Weis-Fogh, he worked with a merry-go-round (a circular revolving platform) of thirty-two grasshoppers. Krogh even took up the development of buds in trees in collaboration with H. Burstrøm.

A superb lecturer, Krogh eventually tired of preparing his talks and in 1934 withdrew from academic duties. But since 1908 he has been known to Danish schoolchildren from his Laerebog i Menneskets Fysiologi, which went through eleven editions. Krogh was a prolific popular author as well as a scholar in the history of science. He enjoyed Kipling and contributed citations to the Oxford English Dictionary.

As a scholar Krogh was gifted, kindly, sympathetic, and inspiring. Physically he was a small man and wore a mustache and goatee. Although universally respected, during World War II he was apparently slated for “liquidation” by the Germans. Forced to go underground, he escaped to Sweden, where he stayed incognito until the end of the war.

Krogh could at times be argumentative, but he was always loyal in his friendships. In 1929, in Boston, he said: “We may fondly imagine that we are impartial seekers after truth, but with a few exceptions, to which I know that I do not belong, we are influenced—and sometimes strongly—by our personal bias; and we give our best thoughts to those ideas which we have to defend.”

Although Krogh declined decorations, he appreciated other tokens of esteem. He was Silliman lecturer at Yale University in 1922, Charles Mickle fellow of the Toronto Medical Faculty in 1925, and Crooper lecturer at Swarthmore College in 1939, and Croonian lecturer at the Royal Society, London, in 1945, the same year in which he was awarded the Baly Medal. He held numerous honorary degrees. In 1916 he became a member of the Royal Danish Society of Sciences, but he resigned when he found its scientific attitude too unprogressive. On his fiftieth birthday Krogh received a Festschrift, Physiological Papers Dedicated to August Krogh (1926), from twenty-two foreign and Danish pupils. In 1939 he was declared an honorary citizen of Grenå.


I. Original Works. A complete catalog of Krogh’s writings is in Meddelelser fra Akademiet for de Tekniske Videnskaber, 1 (1949), 39–50.

II. Secondary Literature. On Krogh and his work see H. C. Hagedorn, “August Krogh,” in Meddelelser fra Akademiet for de Tekniske Videnskaber, 1 (1949), 33–38; G. Liljestrand, “August Krogh,” in Acta physiologica scandinavica, 20 (1950), 109–120; P. Brandt Rehberg, “August Krogh,” in Festskrift, Kobenhavns Universitet 1950 (Copenhagen, 1950), pp. 182–215; and L. G. Rowntree, Amid Masters of Twentieth Century Medicine (Chicago, 1958), pp. 171–174.

E. Snorrason

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Krogh, Schack August Steenberg." Complete Dictionary of Scientific Biography. . 18 Aug. 2017 <>.

"Krogh, Schack August Steenberg." Complete Dictionary of Scientific Biography. . (August 18, 2017).

"Krogh, Schack August Steenberg." Complete Dictionary of Scientific Biography. . Retrieved August 18, 2017 from

Schack August Steenberg Krogh

Schack August Steenberg Krogh

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.

Additional Sources

Schmidt-Nielsen, Bodil, August and Marie Krogh: lives in science, New York: American Physiological Society, 1995. □

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Schack August Steenberg Krogh." Encyclopedia of World Biography. . 18 Aug. 2017 <>.

"Schack August Steenberg Krogh." Encyclopedia of World Biography. . (August 18, 2017).

"Schack August Steenberg Krogh." Encyclopedia of World Biography. . Retrieved August 18, 2017 from

Krogh, Schack August Steenberg

Schack August Steenberg Krogh (shäk ou´gŏŏst stān´bĕrg krôkh), 1874–1949, Danish physiologist. He taught at the Univ. of Copenhagen (1916–45) and studied respiration, circulation, and the effect of an exclusive meat diet on the Eskimo and of deep-sea conditions on living organisms. For his discovery of the regulation of the vasomotor mechanism of the capillaries he received the 1920 Nobel Prize in Physiology or Medicine. His writings include The Anatomy and Physiology of Capillaries (1922, rev. ed. 1959), Osmotic Regulation in Aquatic Animals (1939), and Comparative Physiology of Respiratory Mechanisms (1941).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Krogh, Schack August Steenberg." The Columbia Encyclopedia, 6th ed.. . 18 Aug. 2017 <>.

"Krogh, Schack August Steenberg." The Columbia Encyclopedia, 6th ed.. . (August 18, 2017).

"Krogh, Schack August Steenberg." The Columbia Encyclopedia, 6th ed.. . Retrieved August 18, 2017 from