Born poor in a small village in Ryazan, Russia, physiologist Ivan Petrovich Pavlov (1849-1936) pioneered the study of circulation, digestion, and conditioned reflexes.

"School yourself to demureness and patience. Learn to inure yourself to drudgery in science. Learn, compare, collect the facts," he advised.

Pavlov is best known for his passionate and painstaking 30-years of experiments to determine the brain functions of dogs. From Pavlov, we learned classical conditioning.

He discovered that by repeated association, an artificial stimulus (a bell) could replace a natural stimulus (food) to cause a physiological reaction (salivation).  Pavlov thought that habit, even higher mental activity, relied on a series of conditioned reflexes.

"Facts are the air of the scientists. Without them you never can fly," explained Pavlov, who won the 1904 Nobel Prize for physiology for his research on the digestive system.

"Science demands from a man all his life," he said. "If you had two lives that would not be enough for you. Be passionate in your work and in your searching."

Be patient. Knowledge grows gradually.