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I am a registered marrow donor. You should be too.
I don't consider myself particularly altruistic but when you read a story like this, you know that by giving a drop of blood it just might lead to saving someone's life. I am an organ donor as well. I have the little symbol on my driver's license and if I ever do get squished by a truck, I hope there are parts that can still be used by someone. I won't be using them. I really won't miss them at that point.
In the meanwhile (the interstices between potential squishing incidents), I stand ready to give replicable body parts to someone who may be dying for lack thereof. Like bone marrow. Here's a cordless drill and a straw. Let's get it done. (OK, maybe not that way!)