A diabetic has too much sugar in his blood as well as
sugar in his urine. The fact that diabetic urine is sweet to the taste was
often used amusingly by Dr. Oliver Wendell Holmes, a distinguished American
physician who was also famous as a poet, in his lectures to Harvard medical
students.
He used to point to a beaker of urine on the table and
say: "Now I will demonstrate that urine can be sweet." Then he would
dip his finger into the beaker and taste. After that he would say: "Gentlemen,
would you do the same, please?"
After the demonstration Holmes would smile and then
show his disappointment. "You lack observation, gentlemen – a highly
important factor in medical diagnosis", he would say. "I said I would
demonstrate that urine could be sweet, and you did not note that I put my index
finger in the beaker but tasted my middle finger."