Around 36,000 units of blood were donated to the New York Blood Center in the days after September 11—36,000 donations of 450 milliliters each—as New Yorkers, desperate to do something, encouraged by newscasters and community leaders, and gratified to make some sacrifice, rushed to local blood banks. It wasn’t just New York: There was a two-hour line at a Red Cross office in Madison, Wisconsin, and, in Gaza, Yasser Arafat was photographed waiting to give blood intended for the victims of the attacks, as was nearly every member of Congress in Washington. None of that blood was used, of course. By the time of the congressional blood drive, there were no survivors in need. The country’s blood banks collected close to 600,000 more units in the fall of 2001 than they would have without the prompt of the attacks. But blood cannot be used more than a few weeks after donation, and more than 200,000 of the 9/11 units were simply discarded.