<P> Work to emulate James Blundell continued in Edinburgh . In 1845 the Edinburgh Journal described the successful transfusion of blood to a woman with severe uterine bleeding . Subsequent transfusions were successful with patients of Professor James Young Simpson after whom the Simpson Memorial Hospital in Edinburgh was named . </P> <P> The largest series of early successful transfusions took place at the Edinburgh Royal Infirmary between 1885 and 1892 . Edinburgh later became the home of the first blood donation and blood transfusion services . </P> <P> It was not until 1901, when the Austrian Karl Landsteiner discovered three human blood groups (O, A, and B), that blood transfusion was put onto a scientific basis and became safer . </P> <P> Landsteiner discovered that adverse effects arise from mixing blood from two incompatible individuals . He found that when incompatible types are mixed, an immune response is triggered and the red blood cells clump . The immunological reaction occurs when the receiver of a blood transfusion has antibodies against the donor blood cells . The destruction of red blood cells releases free hemoglobin into the bloodstream, which can have fatal consequences . Landsteiner's work made it possible to determine blood group and allowed a way for blood transfusions to be carried out much more safely . For this discovery he was awarded the Nobel Prize in Physiology and Medicine in 1930, and many other blood groups have been discovered since . </P>

When did blood transfusions become safer and why