Science
One scientist's blood-typing system made transfusions safe
In 1901, Karl Landsteiner mixed blood serum and red cells from his colleagues and found they sometimes clumped and sometimes didn't. He sorted the pattern into blood groups A, B and O, explaining why some transfusions killed patients while others worked fine. The ABO system he defined is still checked before every transfusion today, and won him the 1930 Nobel Prize in Physiology or Medicine.