This is one of my favorite stories. I didn't write it, of course, but I modified it slightly. I got it from a handbook at a Christian Camp I went to in middle school. It's sad, but it's powerful:
The first panic set in after the disease broke through the quarantine. NATO and the Center for Disease Control could do nothing after this. What had begun as an ordinary flu in a remote village in India had now become a worldwide epidemic. That first week, after the flu was discovered, nearly 70 000 people had died. Now more than this were dying every day, and the flu had spread into every country and nation. There was no escaping it.
Miraculously enough, however, overwhelming dread of the virus changed into a weak hope as an emergency broadcast announced that the DNA code of the flu virus had been broken, and that a cure was possible. However, clean, uninfected blood was needed. The announcement strongly urged everyone that hadn't already caught the disease to go to the nearest hospital and have their blood taken. That was it--they just needed clean blood that had been exposed, but not infected.
After hours of standing in lines at the hospital, a nurse finally draws blood from you, your wife and kids. In another hour an updated posting is made. All of your family is listed as able to leave except your one and only son. As you stand, wondering why he was missed, a voice announces a name over the intercom. Straining to hear the following directions, you don't notice your son tugging on your jacket as he says, "Daddy, that's me." Before you know it, they have grabbed your boy. A doctor runs up to you waiving a clipboard and says, "It's okay, his blood is clean. His blood is pure. We need to make sure he doesn't have the disease. We think he has the right type."
But the doctor is not smiling. As he pulls you aside, he tells you "We didn't realize that the donor would be a minor and we need...we need you to sign a consent form." You begin to sign and then you see that the number of pints of blood to be taken is empty. "H-h-h-how many pints?" you ask.
The doctor frowns. "We had no idea it would be a little child. We weren't prepared. We need it all! We are talking about the world here. Please sign. We need it all--all of it!" "But can't you give him a transfusion?" you ask. "If we had clean blood we would. Can you sign? We need you to sign!" In numb silence you do. "You can have a few moments with him before we begin," the doctor says, "but we need to hurry."
With tears in your eyes, you approach the steel table your son lies on. He already has tubes and wires attached to him. His mouth whispers, "Daddy? Mommy? What are they doing?" but his eyes show his pain more than his questions. "Son, we love you. This has to happen; do you understand?" It is obvious that he doesn't, yet he nods anyway. The doctor comes back in and says, "I'm sorry, we've got to get started. People all over the world are dying."
The next week, when they have the ceremony to honor your son, only a few people show up. Others don't come because they'd rather go to the lake. Some come with a fake smile and only pretend to care, mostly because they don't understand what you gave, and how your only son gave his life to save them.
edit: fixed a typo (was "fly," was supposed to be "flu")