Pavlov used proved his theory of classical conditioning by studying salivation in dogs. He observed an unconditioned response, the salivation, that was a consequence of an unconditioned stimulus (the meat). Then, he paired the unconditioned response with a neutral stimulus (the sound of a bell), by giving the dog the meat after ringing the bell. He found that after being conditioned, the dog salivated every time he heard the bell ring, the salivation was now a conditioned response.
As a result of the rule limiting the size of the House of Representatives to _435 members, U.S. congressional districts on average now have very substantial populations
