SPUTNIK / SCIENCE PHOTO LIBRARY SPUTNIK / SCIENCE PHOTO LIBRARY
Ivan Petrovich Pavlov (1849-1936), second from right, Russian psychologist and physiologist. His most famous work was on the reflex actions in animals, notably the idea of conditioning of reflexes by repeated reward or punishment stimuli. Pavlov won the 1904 Nobel Prize for Physiology or Medicine. Photographed during the opening ceremony of the 25th International Conference of Physiologists held in Leningrad, 1935.
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