I gave blood for the first time last Friday. Always meant to do it, and here was a ridiculously convenient opportunity. So I went.

I was never sqeamish as a child. I remember being freaked out my a wax stature of a man raising the severed head of another man at some history museum in Dover, but I was equally fascinated by it.

Anyway, I was disturbed to notice that I was growing squeamish in my old age, especially concerning damage to blood vessels. And, I suddenly realised,...