Karl Landsteiner discovered in 1900 the reason different blood types sometimes led to deadly transfusions – and he did it by testing on his employees.

According to the National Library of Medicine,
“Landsteiner discovered the ABO blood group system by mixing the red cells and serum of each of his staff. He demonstrated that the serum of some people agglutinated the red cells of other. From these early experiments, he identified three types, called A, B and C (C was later to be re-named O for the German “Ohne”, meaning “without”, or “Zero”, “null” in English). The fourth less frequent blood group AB, was discovered a year later.

For this revolutionary life-saving research, Landsteiner was awarded the Nobel Prize in physiology and medicine. Though we’d like to add an honorable mention to the employees of Landsteiner who literally shed their blood for these results.