In 1874, French neurologist Jean-Martin Charcot published a series of papers describing a horrible nerve disease. It begins with weakness, stiffness, and spasms in the arms and legs. Over the course of about a year, muscles stop working, and with them goes the ability to walk, stand, and speak. Then the tongue and lips stiffen. The mouth gets stuck partway open, accentuating laugh lines and giving "an appearance of weeping," Charcot wrote. "Finally, the vagus nerve is affected with grave difficulty breathing, leading to death of a person already so weakened by insufficient nourishment."

Charcot was also an expert pathologist. After performing autopsies on several of these patients, he ...