Portrait of Russian physiologist Ivan Petrovich Pavlov (1849-1936) painted by M. V. Nestenov in 1935. Pavlov is known for his work on reflexes. He performed several experiments on the digestive physiology of dogs which earned him the 1904 Nobel Prize for medicine & physiology. He showed that nerves stimulated by the presence of food in the dog's mouth carried a message to the brain, which, in turn, via other nerves, stimulated the secretion of gastric juices. He also showed that if a bell is made to ring every time a dog is shown food, he will eventually salivate when the bell rings, even though no food is shown him. This was the first example of a conditioned reflex.