August Krogh
A Danish scientist who unlocked the secrets of how our capillaries deliver life-giving oxygen, a discovery that earned physiology's highest honor.
1874–1949 (age 75)·Danish physiologist·Birthday: November 15·The Gilded Age
Biography
August Krogh approached the mysteries of the living body with the mind of a master detective and the hands of a gifted inventor. At the University of Copenhagen, he wasn't content with mere observation; he built the tools needed to see physiology in action. His most famous insight, now enshrined as Krogh's Principle, was elegantly simple: for every biological problem, there is an organism perfectly suited to solve it. He proved this by studying how insects breathe and, most famously, how capillaries—the body's tiniest blood vessels—regulate blood flow. Before Krogh, it was debated whether these vessels were passive tubes or active gatekeepers. Through painstaking experiment, he demonstrated they opened and closed in response to local tissue needs, a fundamental mechanism for life. This work won him the Nobel Prize in 1920. Beyond capillaries, his inventive spirit led to pioneering studies in exercise physiology, respiratory gas exchange, and even the development of a clinical apparatus for measuring metabolic rate, leaving fingerprints across the entire field of modern physiology.
The Gilded Age
1860–1882
Born during or after the Civil War, they built industrial America — the railroads, the steel mills, the first skyscrapers. An era of massive wealth, massive inequality, and the belief that the future belonged to whoever could build it fastest.
August was born in 1874, placing them squarely in The Gilded Age. The events that shaped this generation — world wars, depression, and rapid industrialization — shaped the world they entered and the choices available to them.
#1 When August Was Born
The biggest hits of 1874
August's Life & Times
The world at every milestone
1874Born
President: Ulysses S. Grant
1879Started school
President: Rutherford B. Hayes
1887Became a teenager
President: Grover Cleveland
1890Could drive
Wounded Knee massacre marks the end of the Indian Wars
President: Benjamin Harrison
1892Could vote
President: Benjamin Harrison
1895Turned 21
First public film screening by the Lumiere brothers
President: Grover Cleveland
1904Turned 30
New York City opens its first subway line
President: Theodore Roosevelt
1914Turned 40
World War I begins
President: Woodrow Wilson
1924Turned 50
First Winter Olympics held in Chamonix, France
President: Calvin Coolidge"It Had to Be You" — Isham Jones
1934Turned 60
Gas: $0.19/galPresident: Franklin D. Roosevelt"Stars Fell on Alabama" — Jack TeagardenBest Picture: It Happened One Night
1944Turned 70
D-Day: Allied forces land at Normandy
Gas: $0.21/galHome: $3,400Min wage: $0.30/hrPresident: Franklin D. Roosevelt"Swinging on a Star" — Bing CrosbyBest Picture: Going My Way
1949Died at 75
NATO founded; Mao proclaims the People's Republic of China
Gas: $0.27/galHome: $7,450Min wage: $0.40/hrPresident: Harry S. Truman"Riders in the Sky" — Vaughn MonroeBest Picture: All the King's Men
Key Achievements
- Awarded the Nobel Prize in Physiology or Medicine in 1920 for discovering the mechanism of capillary motor regulation.
- Formulated 'Krogh's Principle', a foundational concept in comparative physiology and experimental biology.
- Made significant contributions to respiratory physiology, explaining gas exchange in both human lungs and insect tracheae.
- Invented several key scientific instruments, including a precision spirometer and an apparatus for measuring metabolic rate.
Did You Know?
His wife, Marie Krogh, was also a accomplished physiologist and co-authored important research with him on capillary function.
He conducted early, rigorous studies on the physiology of bicycle racing in collaboration with champion cyclist Carl Olsen.
During World War II, he was actively involved in helping Danish Jews escape to Sweden.
A genus of parasitic crustaceans, 'Kroghia', is named in his honor.
““For such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied.””
