I'm no longer able to talk intelligently about blood types. But I still remember how exciting it was in early forties to learn that blood types were not limited to O, A, B, and AB. The occurrence of severe reactions to carefully typed blood in patients who had previously been transfused led to the discovery of still one more subtype, which was called Rh, from studies on rhesus monkeys.

There are many URLs about blood types, but I did not think any of them worth citing here.