Despite medical milestones in the early 1900s, including Karl Landsteiner's discovery of blood types that enabled surgeons to perform safe blood transfusions, patients still suffered from reactions to contaminants. In the 1920s and 1930s, scientists began to devise ways to detect bacteria in transfused blood. Two doctors at the University of Pennsylvania School of Medicine created a device to freeze-dry serum, the clear fluid in the blood that contains the proteins and antibodies formed by the body's immune system to protect against infection. The doctors, Earl W. Flosdorf and Stuart Mudd, used the dried serum for transfusions and to prevent some childhood diseases. Flosdorf and Mudd first described their procedure at an American Chemical Society meeting that took place this month in 1934.

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