Even in the frozen center of Massachusetts winter, my college campus was ripe for the blood harvest. Red Cross banners were everywhere, always. I felt compelled to volunteer myself in part because it seemed such a blameless cause that I could think of no reason not to, and easy charity is de rigeuer for the college kid. But the first time I tried to sign up for an appointment, I was turned away. Somebody I vaguely knew — a student liaison for the Red Cross — looked up at me from behind a table in our echoing humid dining hall and told me, without asking my weight, that I wasn’t heavy enough to give blood. My winter coat dwarfed me, but she was still right: The Red Cross asks that donors be 110lbs, and I weighed only 100.