Renato Dulbecco was a pioneer in the field of virology, the study of viruses. He began as a practicing physician in the military service of his native Italy during World War II and continued to practice as physician with partisan units fighting the German occupation of that country near the end of the war. It was only with his immigration to the United States in 1947 that he began his lengthy and highly distinguished second career in scientific research. Dulbecco developed the plaque assay technique which allowed scientists to quantify the number of viral units in a laboratory culture, thus making possible most of the later major discoveries in virology. Dulbecco later devoted most of his life to the study of viruses that could cause cancer in animals and human beings. For his work in this field, Dulbecco shared the Nobel Prize in medicine or physiology in 1975 with microbiologist...