(1849-1936) a Russian scientist who won the Nobel Prize for Medicine for his work on the digestive system. He is famous especially for his work with dogs, which proved the existence of the conditioned reflex (=a physical reaction that you cannot control, caused by repeated training or experiences). Each time he fed his dogs he rang a bell before giving them their food. The dogs learned to connect the ringing of the bell with the arrival of the food, and they got excited and began to salivate when they heard the bell, even if there was no food.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.
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