20th century
Only in 1901, when the Austrian Karl Landsteiner discovered three human blood groups (O, A, and B), did blood transfusion achieve a scientific basis and become safer.Landsteiner discovered that adverse effects arise from mixing blood from two incompatible individuals. He found that mixing incompatible types triggers an immune response 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. Landsteiners work made it possible to determine blood group and allowed blood transfusions to take place much more safely. For his discovery he won the Nobel Prize in Physiology and Medicine in 1930; many other blood groups have been discovered since.George Washington Crile is credited with performing the first surgery using a direct blood transfusion in 1906 at St. Alexis Hospital in Cleveland while a professor of surgery at Case Western Reserve University.Jan Janský also discovered the human blood groups; in 1907 he classified blood into four groups: I, II, III, IV. His nomenclature is still used in Russia and in states of the former USSR, in which blood types O, A, B, and AB are respectively designated I, II, III, and IV. Dr. William Lorenzo Mosss (1876–1957) Moss-blood typing technique of 1910 was widely used until World War II.William Stewart Halsted, M.D. (1852–1922), an American surgeon,  performed one of the first blood transfusions in the United States.
The prevalence of type O blood among Indigenous people of the Andean region meant such procedures would have held less risk than blood transfusion attempts among populations with incompatible blood types, which contributed to the failures of early attempts in Europe. Animal blood
Working at the Royal Society in the 1660s, the physician Richard Lower began examining the effects of changes in blood volume on circulatory function and developed methods for cross-circulatory study in animals, obviating clotting by closed arteriovenous connections. The new instruments he was able to devise enabled him to perform the first reliably documented successful transfusion of blood in front of his distinguished colleagues from the Royal Society.According to Lowers account, "...towards the end of February 1665 [I] selected one dog of medium size, opened its jugular vein, and drew off blood, until its strength was nearly gone. Then, to make up for the great loss of this dog by the blood of a second, I introduced blood from the cervical artery of a fairly large mastiff, which had been fastened alongside the first, until this latter animal showed ... it was overfilled ... by the inflowing blood." After he "sewed up the jugular veins", the animal recovered "with no sign of discomfort or of displeasure". Lower had performed the first blood transfusion between animals.