Pavlov&;s experiment on dogs shows

In Pavlov's classic experiments, the salivation normally induced by placing meat in the mouth of a dog was studied. A bell was rung just before the meat was placed in the dog's mouth, and this was repeated a number of times until the animal would salivate when the bell was rung even though no meat was placed in its mouth. In this experiment, the meat placed in the mouth was the unconditioned stimulus (US), the stimulus that normally produces a paicular innate response. The conditioned stimulus (CS) was the bell ringing.Ref: Ganong's Review of Medical Physiology, Twenty-Third Edition