Engraving showing the transfusion of a dog's blood into a man, 1692. Blood is let out of the patient's right arm while a dog's blood is transfused into his left arm. Beginning with Harvey's experiments with circulation of the blood, research into blood transfusion began in the 17th century, with successful experiments in transfusion between animals. However, successive attempts by physicians to transfuse animal blood into humans gave variable, often fatal, results. Early transfusions between humans were risky and many resulted in the death of the patient. It was not until 1901, when the Austrian Karl Landsteiner discovered human blood groups, that blood transfusions became safer.