Human blood is grouped into four different types. These four different types are : A, B, AB, and O. As you might guess, AB is a combination of, well, A and B. Each letter refers to a kind of antigen (protein) on the surface of the red blood cells. Red blood cells and other formed elements only make up about 45% of blood, the other 55% is this watery, sticky substance called plasma. For example, a person with type A blood would have A-antigens on the surface of every last little one of their red blood cells.
Each blood type is also grouped by its Rhesus factor, or Rh factor. Blood is either Rh positive, or Rh negative. About 85% of Americans have Rh+ blood. Rhesus refers to another type of antigen.
I have chosen the most complex type of blood of all: type AB blood. Type AB blood included both A, B, and Rh antigens all at once on all the red blood cells, pretty exciting huh.
Blood transfusions started around 1600, when a scientist tried to transfuse animal blood into a human... disastrous. Then they got a brighter idea... human blood for humans! What a winner. As far as transfusions go (when a person is in need of blood, they can get a transfusion of another person's [a donor] blood. The donor's blood must be in perfect condition though.) type AB blood people can receive blood from any donor. For example, you can not give a type O person (type O means that there is no antigens on the blood cells) type A or type B because their body would create antibodies for the A or B antigens and that would create a whole mess and a lot of trouble for them, which could lead to...