It is recounted that at King’s College in the Strand around the time of the war, the Chief of Services would inevitably begin the year’s rounds by teaching "a singularly important principle of medicine." He asked a nurse to fetch him a sample of urine. He then talked at length about diabetes mellitus. "Diabetes," he said, "is a Greek name; but the Romans noticed that the bees like the urine of diabetics, so they added the word mellitus which means sweet as honey. Well, as you know, you may find sugar in the urine of a diabetic..."By now, the nurse had returned with a sample of urine which the registrar promptly held up like a trophy. We stared at that straw colored fluid as if we had never seen such a thing before. The registrar then startled us. He dipped a finger boldly into the urine, then licked his finger with the tip of his tongue. As if tasting wine, he opened and closed his lips rapidly. Could he perhaps detect a faint taste of sugar? The sample was passed on to us for an opinion. We all dipped a finger into the fluid, all of us foolishly licked that finger."Now," said the Registrar grinning, "you have learned the first principle of diagnosis. I mean the power of observation."We were baffled. We stood near the sluice room outside the ward, and in the distance, some anonymous patient was explosively coughing. "You see," the registrar said continuing triumphantly, "I dipped my MIDDLE finger into the urine, but licked my INDEX finger, not like all you chaps."