Oswald Theodore Avery is little known outside of the scientific community. Yet, this extraordinary man, here brought vividly to life by a perceptive friend and sophisticated scientific colleague, was a monumental force in the development of medical research in the United States. Even among scientists, Avery is known chiefly as the senior author of a paper published in 1944 that identified DNA as the purveyor of genetic information. Two things make this highly personalized biography a landmark volume. First, its technical chapters clarify the philosophical concepts that lie behind today's understanding of the immunology of bacterial infection. Second, not a single existing textbook has ever described the laborious methods by which the men in Avery's laboratory discovered the genetic import of DNA