Keratin Keratin Keratin () is one of a family of fibrous structural proteins. It is the key structural material making up hair, horns, claws, hooves, and the outer layer of human skin. Keratin is also the protein that protects epithelial cells from damage or stress. Keratin is extremely insoluble in water and organic solvents. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals. The only other biological matter known to approximate the toughness of keratinized tissue is chitin. Keratin derives from Greek ' from '
The dogs and the lion's skin The dogs and the lion's skin The dogs and the lion's skin is a fable ascribed to Aesop and is numbered 406 in the Perry Index. However, it is only found in a mediaeval Greek manuscript claiming to be a translation from the Syriac (Syntipas, Fable 19). The story relates how some dogs, finding the skin of a lion, began to tear it to pieces. Seeing them, a passing fox remarked, "If this lion were alive, you would soon find out that his claws were stronger than your teeth." The moral in the original commented that "the fable is for