title: ABO blood group system
context: The ABO blood types were first discovered by an Austrian Physician Karl Landsteiner working at the Pathological-Anatomical Institute of the University of Vienna (now Medical University of Vienna). In 1900, he found that blood sera from different persons would clump together (agglutinate) when mixed in test tubes, and not only that some human blood also agglutinated with animal blood.[5] He wrote a two-sentence footnote:
question: Who first identified blood types?
answers: Karl Landsteiner