What is the X in X-mas?
Austrian-born American pathologist who discovered the human blood groups A, B, and O in 1901. In 1902, his colleagues discovered a fourth group, AB, and in 1927 Landsteiner discovered two more groups, M and N. For this work Landsteiner received the 1930 Nobel Prize for physiology or medicine. In 1940 he discovered the Rh factor.
Austrian American immunologist and pathologist who received the 1930 Nobel Prize for Physiology or Medicine for his discovery of the major blood groups and the development of the ABO system of blood typing that has made blood transfusion a routine medical practice.