Diabetes doesn't come from simply eating too much sugar; nor is it cured, as was once thought, by a little horseback riding. It is not the result of a failing kidney, overactive liver or phlegmy disposition, though these were the authoritative answers for centuries. Diabetes happens when the blood becomes saturated with glucose, the body's main energy source, which is normally absorbed by the cells -- which is to say that the pathology of diabetes is subtle and invisible, so much so that a third of the people who have it don't even know it. Until the prohibition against autopsies was gradually lifted (by 1482, the pope had informally sanctioned it), what we knew of human anatomy came through the tiny window of war wounds and calamitous gashes -- and even then it took centuries for doctors to decide just what the long, 2 lumpy organ called the pancreas actually did or, in the case of diabetes, didn't do. We like to think surgically about the history of medicine, that it moved purposefully from insight to insight, angling closer to cure. But that is only the luxury of contemporary life. Looked at over time, medicine doesn't advance as much as grope forward, with remedies -- like bloodletting, quicksilver ointments and simple, unendurable hunger -- that blurred the line between treatment and torture.