August Krogh was a pioneering Danish physiologist born on November 15, 1874, in Grenaa, Jutland, Denmark. He studied zoology at the University of Copenhagen where he would later become professor of animal physiology in 1916. Krogh established himself as a leading figure in physiological research during his early career, initially working as an assistant to Christian Bohr at the Copenhagen Medical School. His foundational work began while still a student, conducting experiments that would eventually lead to his most significant discoveries. In 1908, he was appointed Associate Professor of Zoophysiology at the University of Copenhagen, becoming the first head of the laboratory for animal physiology at the institution.
Krogh received the Nobel Prize in Physiology or Medicine in 1920 for his groundbreaking discovery of the mechanism of regulation of capillaries in skeletal muscle, demonstrating how blood perfusion adapts to tissue demands through the opening and closing of arterioles and capillaries. He was the first to describe this precise regulatory mechanism which fundamentally transformed understanding of circulatory physiology. Beyond his capillary research, Krogh made seminal contributions to respiratory physiology, developing the microtonometer for quantifying gas transport in blood and demonstrating that oxygen transport across alveoli membranes occurs through passive diffusion. His technical ingenuity led to the invention of numerous scientific instruments including the spirometer, precision pipettes, and improved methods for gas analysis, which became indispensable tools for physiological research worldwide.
Krogh's influence extended beyond pure research as he co-founded what is today the Novo Nordisk company, initially establishing Nordisk Insulinlaboratorium to produce insulin after his wife developed diabetes. He pioneered the use of radioactive isotopes in biological research through collaborations with Nobel laureates Niels Bohr and George de Hevesy, securing Denmark's first cyclotron for physiological studies. Throughout his prolific career, Krogh published over 300 research papers across diverse physiological domains including osmotic regulation, respiratory mechanisms, and exercise physiology where he developed the famous bicycle ergometer. His legacy continues to shape modern physiology with the Krogh Principle remaining a fundamental concept that guides researchers to select the most appropriate organism for studying specific physiological phenomena.
