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Skin. Coloured scanning electron micrograph (SEM) of a freeze-fractured section through human skin. At top is the stratum corneum (pale yellow) of the epidermis, a cornified layer composed of flattened, dead skin cells which form the surface of the skin. The dead cells from this layer are continuously being shed and replaced from cells from the living epidermal layer below (purple). The lowest layer seen here is the dermis (pale yellow and purple strands). This is a thick layer of fibrous connective tissue which supports and nourishes the epidermis. The skin is the body's largest organ, accounting for around 15% of the body's weight. Magnification unknown. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER)