Ivan Petrovich Pavlov (1849-1936), world famous Russian physiologist became second to Freud as the most influential psychologist of our century. Pavlov was a follower of "The father of Russian psychology," Sechenov, whose theory was that the reflex is the essence of all reactions. Pavlov went further and discovered that the conditional reflex is a response, which is not directly connected with the stimulus, but caused by association with a previous experience. The conditioned reflex was discovered in the following experiment on a dog. A bell rung just before a dog was fed; the dog salivated on receiving its food. After repeated trials, the