The body is the most complex machine in the world, and the only one for which you cannot get a replacement part from the manufacturer. For centuries, medicine has reached for what's available--sculpting noses from brass, borrowing skin from frogs and hearts from pigs, crafting eye parts from jet canopies, and breasts from petroleum by-products. In Replaceable You , Mary Roach sets sail on the uncharted waters of regenerative medicine, exploring the remarkable advances and difficult questions prompted by the human body's failings. When and how does a person decide they'd be better off with a prosthetic than their existing limb? Is there a sensitive way to harvest tissue and bones from the deceased? Which animals might be the best organ donors? Through interviews with patients, physicians, pathologists, engineers, and scientists, Roach immerses readers in the wondrous, improbable, and surreal quest to build a new you.