An old G.P. and his nurse were on the train, going to a Medical Conference. Opposite them was a man furiously scratching his elbow.

"I wonder what's the matter with him?" asked the nurse.

"He's a patient of mine and, in confidence, I can tell you that he suffers badly from hemorroids," replied the G.P.

"Well, why he's scratching his elbow?" asked the puzzled nurse.

"Oh, he's a politician, and he doesn't know his ass from his elbow."