"...When the body performs work, this greatly increases its need for oxygen, especially in the muscles, but the question was where this increased oxygen supply came from. The capillaries had been known for 250 years. The conventional view was that they all stood open. It was assumed that the speed of blood flow increased during work
. Krogh's mathematical calculations indicated that this could not be true. Faster blood flow through the capillaries hardly increased the potential for more oxygen supply, because the time for diffusion meanwhile decreased.
Instead, Krogh elegantly and clearly demonstrated (by measurements of the oxygen content in capillaries and muscle fibers, direct observations and histological sections) that a relatively small number of capillaries are open during rest. In fact, capillaries are opening and closing all the time. During work, however, more capillaries are open. He also found that capillaries can vary in diameter and are thus independently contractile. Although the speed of blood flow through the capillaries is the same during rest and work
, the oxygen supply increases because so many capillaries are open and each capillary can hold more blood...."
"Schack August Steenberg Krogh - A Versatile Genius"
The Nobel Prize in Physiology or Medicine 1920
"A Monumental Contribution to Research in Integrative Physiology"
Nobel Lecture, December 11, 1920:
"A Contribution to the Physiology of the Capillaries"
August Krogh was awarded the Nobel Prize in Physiology or Medicine in 1920 "for his discovery of the capillary motor regulating mechanism." During the 1939-40 Winter War between the Soviet uni0n and Finland, when the Danes began collecting money in support of Finland, August Krogh was urged to donate his Nobel medal, which was made of solid gold, for this purpose. He did so, but first he had his daughter Bodil Schmidt-Nielsen make a copy of the medal in silver, which was then gold-plated.