few scientific data remain valid if isolated from the philosophical stream that bore them, from the social setting where they were elaborated, and from the instrumentation that characterized the research of the period in which they originated. Pavlov’s contribution, the introduction of the method of conditioning and the recognition of the implications of the conditional reflex, is among those which do. Fulton’s statement that “Pavlov was one of the five or six individuals of the last generation who caused mankind to think in new terms; like Freud, he created a new horizon, but, unlike Freud, he seemed wholly objective in his mode of collecting scientific data” is now generally accepted.