Tomorrow is the birthday of Francis Peyton Rous, an American pathologist known for his pioneering research on cancer. In 1909, Rous was given a Plymouth Rock chicken with a large breast tumor, and he experimented by transferring a cell-free filtrate of the tumor into healthy chickens. Surprisingly, the same spindle-cell sarcoma tumors developed in the healthy chickens. Flying in the face of contemporary ideas about cancer, Rous suggested that a virus triggered the tumors. But he was unable to produce similar results in mammals, and the idea was not taken seriously. In the 1930s Rous resumed cancer research when it was shown that a virus caused wild rabbits to develop skin warts and papilloma. Using this new animal model, Rous showed that viruses, chemicals such as tar, and radiation can collaborate to enhance tumor development. For his 1910 discovery that a virus can cause cancer, Rous was awarded a share of the Nobel Prize in medicine in 1966. He died in 1970.