Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
August Krogh (1874-1949), Danish physiologist, showed that diffusion is the process by which oxygen passes through capillary walls into tissue. As muscles respond to a stimulus and more oxygen is needed, more capillaries open up to provide extra blood flow and with it oxygen to the muscle. For this discovery of the capillary motor mechanism he was awarded the 1920 Nobel prize in Physiology.