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This is a little off topic here, but seems close enough.
I've wanted to learn how to do a field blood transfusion, just in case. I'm pretty sure I have type O something blood. I've donated a few times, and the nurses are always impressed with my blood, to the point of cutting me in front of a half hour long line in a high school blood drive once. Apparently I have really high iron, as well. One of the times I donated they brought in gear for, if I remember correctly, a double apheresis [sp?] procedure. As far as I know, I was one of only two who did that, the other being a P.E. teacher. I was supposed to be told at a later time what my blood type was exactly, but never got anything.
Anyway, it just seems like something that would be really useful to know.