Francis Peyton Rous was born in 1879, in Baltimore, Maryland, to Charles Rous, a grain exporter, and Frances Wood, the daughter of a Texas judge. He pursued his biological interests at Johns Hopkins University, receiving a B.A. in 1900 and an M.D. in 1905. After a medical internship at Johns Hopkins, however, he decided to concentrate on research and the natural history of disease. In 1909, Simon Flexner, director of the newly-founded Rockefeller Institute in New York City, asked Rous to take over cancer research in his laboratory.

A few months later, a poultry breeder brought a Plymouth Rock chicken with a large breast tumor to the Institute and Rous, after conducting numerous experiments, determined that the tumor was a spindle-cell sarcoma. When he transferred a cell-free filtrate from the tumor into healthy chickens of the same flock, they developed identical tumors. Moreover, after injecting a filtrate from the new...