Thursday is the birthday of Ivar Pavlov, a Russian physiologist born in 1849 who is best known for his studies of the conditioning of dogs. Between 1890 and 1900, Pavlov investigated the secretory mechanisms of digestion in animals. In his most famous experiment, he fitted dogs with a tube on the cheek to measure their saliva production. Each time Pavlov showed the dogs food, he rang a bell, a neutral stimulus with no natural meaning for the dogs. He discovered that if this association was repeated enough times, the bell ringing alone would trigger salivation. Pavlov was awarded the Nobel Prize in physiology or medicine in 1904 for his 1897 work, "Lectures on the Work of the Principal Digestive Gland," which summarized his research findings.
[Source: Roy Porter, Ed., The Biographical Dictionary of Scientists (Oxford University Press, ed. 2, 1994).]