When I was young, my mother told me about a short story she'd read when she was young. Of course, the name was long gone.
The story is about guy with an itch on one of his knuckles. He repeatedly scratches it, but the itch persists. Somehow (hopefully in an interesting fashion), he learns that the itch is an attempt to communicate by a microscopic civilization that's developed on his knuckle. Again, somehow, he finds a way to communicate with them and learns that his scratching is wreaking havoc on their world and they plead with him to stop. The guy waits for a short while and then scratches again, thinking that the few minutes that he didn't scratch should've given them a few centuries of peace.
Anyone remember the name of this one?