25 Interesting Facts About Human Blood

Karl Landsteiner discovered blood types in 1901 by observing that blood from people of different types would clot when mixed together. He later classified them as A, B and O. Karl Landsteiner discovered blood types in 1901 by observing that blood from people of different types would clot when mixed together. He later classified them as A, B and O. Blood type refers to different molecules on the surface of red blood cells. A mismatch of these molecules between donor and recipient can trigger a fatal immune reaction after a blood transfusion, as the recipient’s body attacks the outsider blood.