For most of history, medical practitioners thought bloodletting, not blood transfusion, would cure an ailing person. Although Spanish colonizers reported the Incas transfused blood, most of the world still opened veins or used leeches to rid the body of so-called "bad blood."
It wasn’t until the late 1800s when scientists realized that blood transfusion could save lives. But they still didn’t understand blood typing, and many transfusions were unsuccessful. In 1900, Karl Landsteiner, a Viennese researcher, identified the main blood types, and how they were distinct. In 1937, he was part of a research team that identified the Rhesus factor (now called Rh factor).
Blood donation and banking began in the 1950s in the U.S. and evolved into a major, lifesaving operation. Almost 5 million patients in the U.S. need a blood transfusion each year, which means a person is in need of blood every two seconds, according to the American Red Cross.