blood transfusions - work of Landsteiner
Before 1901 blood transfusions had often been fatal but nobody knew why
1901 Karl Landsteiner discovered blood groups (A,B,AB,O) and this paved the way for blood transfusions to be carried out
This would help people who had blood disorders such as anaemia and leukaemia
identifying blood groups therefore paved the way for safe person to person blood transfusions