SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Hair. Historical artwork of a section of the root of a human hair. Hair (brown) consists of dead cells containing keratin, a strong, fibrous protein. The root of each hair is embedded in a skin follicle (pink). The hair shaft consists of a semi-hollow core (medulla, down centre), a surrounding layer of long, thin fibres (cortex, brown) and outer layers of overlapping cells (cuticle). Hair is formed when new cells produced in the bulb of the root (not seen) push up older cells, which then become keratinised. Taken from a book by the Swiss physiologist Rudolf Albert von Kolliker (1817-1905).
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