Why was the discovery of blood group significant?
For a long time, doctors had noticed that about half the patients who recieved blood transfusion developed severe reactions that proved fatal. It was not until 1901, when the Austrain Karl Landsteiner discovered human blood groups, that blood transfusions became safer. It was found that the mixing of blood from two individuals during a transfusion, can lead to blood clumping. The clumped red cells can crack, and cause toxic reactions. This can cause the death of a patient.
Karl Landsteiner discovered that blood clumping was a reaction which occurs when the reciver of a blood transfusion has antibodies against the donor blood cells. He also discovered that there were three human blood groups.
These were A, B, and O blood groups. To avoid such reaction, transfusions should take place only between people of the same blood group. Nobel Laureate Karl Landsteiner was involved in the discovery of both the A,B and O blood groups in 1901, and the AB group later on.