Pavlov always signaled the occurrence of food by ringing a bell

He is best know for the establishment of what he called "conditional reflexes" — i.e., reflex responses, like salivation, that only occurred conditionally upon specific previous experiences of the animal.

Experiments were carried out in the 1890s and 1900s, general theory of the origin and development of the fixed inherited behavior patterns of animals

Try your hand at creating a "Conditional Reflex" in Pavlov's dog

Pavlov’s dog

Ethology as a field was considered to have begun during the 1930s with the work of Dutch biologist Nikolaas Tinbergen and Austrian biologists Konrad Lorenz and Karl von Frisch, joint winners of the 1973 Nobel Prize in Physiology or Medicine.^[1]