Blood loss was a huge problem with surgery in the 18th and 19th century. Many amputations were done and due to the simplicity of the tools used blood loss was a factor which caused death amongst patients whilst on the operating table. When Karl Landsteiner discovered blood groups in 1901 it became possible for surgeons to transfer blood to patients to replace blood that was lost during surgery. This came into full effect during the world wars as blood transfusions helped soldiers with their war injuries. Also because of Karl Landsteiner blood didn't clot as the correct types were used. Another problem was that the plasma would separate from the corpuscles but this was tackled through the discovery of sodium citrate stopping this from happening. Also since tools improved and knowledge of blood vessels improved as well surgeons realised how to manoeuvre their surgical technique to minimise blood loss.