A blood transfusion is the transfer of blood from one living thing into the bloodstream of another.
In the 1660s, several scientists experimented with such transfusions. Richard Lower had some success transfusing blood between dogs. Then he injected lamb blood into humans, and a patient died, which led to blood transfusions being outlawed.
In 1818, James Blundell gave a woman blood from her husband. It worked, no problem. But other patients died from transfusions. Decades later, a German named Leonard Landois learned why blood mixing can be fatal: They can make red blood cells clump and even explode. In 1901, American biologist Karl Landsteiner found the reason. Some blood has antigens called A and B. (Antigens are special markers on germs and other substances that cause your body to make antibodies, proteins that defend against invaders.) These antigens are harmful to blood that doesn’t have A or B antigens.
Today, doctors test blood for antigens before doing a transfusion, and as a result, safe transfusions save countless lives.
