Photograph by Sarah Leen
Study in light and shadow, a bodybuilder's back muscles and hand veins bring the topography of skin into vivid relief. A substance of contrasts, the skin is the body's largest organ yet measures only millimeters thick; it forms a barrier to the outside world. It contains blood vessels, veins, nerve fibers and endings, more than two million sweat glands, and millions of fat cells that insulate and protect other organs against minor trauma and the environment. Even the super thin skin that drapes the hand is far from just a protective covering—one square-inch patch of it contains 79 feet (24 meters) of nerve fiber.