I was scrabbling around under the bed trying to retrieve the computer when – ouch – a splinter made its way under my index finger nail. First thing in the morning is not a good time for me to deal with this: I’m peering through lacrimal secretions that are still like gobbets of purest mud, and I need an industrial strength magnifying glass these days. So I left it alone for the moment. It began to hurt.

By the time I’d done a school assembly my eyesight was more conducive to digital inspection so I had a look. I could see a couple of millimeters of wood poking out from the edge of the nail so I grabbed it with a pair of tweezers and yanked. Out it came: about 7 mm of splinter. ‘Good, that looks like all of it, so problem sorted.’

Or so I thought.

That evening, it was still sore. It was beginning to swell. In the middle of the night it was throbbing. In sleepy gloom I’d already been admitted to hospital with septicaemia, and they’d had to amputate my finger, then my hand, then my arm. How much of me would they have to amputate before I stopped being me? Clearly, there was still some wood under the nail.

In the morning the finger end was red, warm, swollen and exquisitely painful. Rubor, calor, tumor, dolor. As soon as I could see, I took a pair of scissors and poked around a bit under the nail. Hell’s teeth, it hurt. There was something dark. Clotted blood or wicked wood? Whatever, it was I dug it out.

Now here’s the wonderful thing.

Within seconds, and I mean seconds, the throbbing abated. Within 15 minutes the redness had all but gone and there was no more swelling. After an hour there was no sign that anything had ever been amiss. I even remarked to SWMBO how marvellous it was.

Isn’t it remarkable how the body is so good at recognizing foreign material? And isn’t it remarkable that having done so, it knows as soon as, but not a minute before, the foreign material is no longer there? Imagine how efficient and busy the cells of the immune system must be to detect, act, repel, contain and relax.

Some scientists want to know exactly how it all works, and good luck to them. I’m happy to know that it still does, after all these years.