In 1901, Austrian American immunologist and pathologist while mixing blood of different people made a groundbreaking discovery saving numerous lives and helping the world in creating blood banks, enabling modern surgery and advancing several other fields. Karl Landsteiner identified the human ABO blood group system after studying what happened when blood samples from different people were mixed. His work explained why some blood transfusions caused dangerous reactions while others could be performed without the same response.
The discovery changed the way doctors understood blood transfusion. Before blood groups were identified, physicians did not have a reliable system for deciding whether blood from one person could be given to another. Transfusions could therefore produce serious reactions. Landsteiner's research showed that blood differs between people and that these differences can cause an immune reaction.
