a story I was told by a friend of mine at King’s college. He said it happened to him, but I have my doubts. He said the Chief of Services began the year’s rounds by teaching “an important principle of medicine.” On this occasion he asked a nurse to fetch him a sample of urine. He then talked at length about diabetes mellitus. ” The Romans noticed that bees like the urine of diabetics, so they added the word mellitus which means sweet as honey and sugar can be found in the urine of a diabetic…” The nurse returned with a urine sample which the registrar showed the students. He then dipped a finger into the urine, then licked his finger with the tip of his tongue to demonstrate whether he could taste sugar; then passed the sample round inviting the students to do the same. They all dipped a finger in the urine and licked it.

The registrar then said: “you’ve now learned the first principle of diagnosis – observation.” This puzzled all the students until he said: “You see,I dipped my middle finger into the urine, but licked my index finger, unlike you lot. I guarantee, it’s a mistake you won’t make twice.”