“Though their doctors dutifully record such distinct entities as stroke, or cardiac failure, or pneumonia, these aged folk have in fact died because something in them has worn out. Long before the days of scientific medicine, everyone understood this. On July 5, 1814, when he was seventy-one years old, Thomas Jefferson wrote to the seventy-eight-year-old John Adams, "But our machines have now been running seventy or eighty years, and we must expect that, worn as they are, here a pivot, there a wheel, now a pinion, next a spring, will be giving way; and however we may tinker them up for awhile, all will at length surcease motion.”