Karl Landsteiner was one of the first scientists to study the physical processes of immunity. He is best known for his identification and characterization of the human blood groups, A, B, and O, but his contributions spanned many areas of immunology, bacteriology, and pathology over a prolific forty-year career. Landsteiner identified the agents responsible for immune reactions, examined the interaction of antigens and antibodies, and studied allergic reactions in experimental animals. He determined the viral cause of poliomyelitis with research that laid the foundation for the eventual development of a polio vaccine. He also discovered that some simple chemicals, when linked to proteins, produced an immune response. Near the end of his career in 1940, Landsteiner and immunologist Philip Levine discovered the Rh factor that helped save the lives of many unborn babies whose Rh factor did not match their mothers. For his work identifying the human blood groups...