Russian physiologist Ivan Pavlov (1849–1936) carried out famous experiments with dogs, which were intended to demonstrate conditioned reflex. Noticing that the laboratory dogs would sometimes salivate merely at the approach of the lab assistants who fed them, Pavlov, who was already a Nobel laureate for his research on digestion, set out to determine whether he could turn normally “unconditioned” reflexes or responses of the central nervous system into conditioned reflexes. He demonstrated that if a bell is rung every time a dog is fed, eventually the dog becomes conditioned to salivate at the sound of a bell, even if there is no food present. In this way, Pavlov substituted artificial stimulus (the ringing of the bell) for natural or environmental stimulus (food) to prompt a physiological reaction (salivation). Based on these experiments, Pavlov concluded that all acquired habits depend on chains of conditioned reflexes. This conclusion contributed to the development of behaviorism.