Biologists and histologists use different terms for sections of the skin than do tanners. The fine structure of the component collagen fibres is described. The size and shape of the component amino-acids determine the shape of the molecule. Hydroxyproline, with a bulky side-chain, plays an important role in determining space between chains, degree of hydrogen bonding (responsible for the strength and stability of the collagen molecule) and the shrinkage temperature. The more there is present, the greater the amount of bonding and the higher the shrinkage temperature. Mammalian skin (ts 65 c) has twice as much as fish skin (ts 40 c). The function of electrostatic and covalent bonds is described, as well as the appearance of collagen fibrils and fibres under the electron microscope. The fibres form fibre bundles but these differ depending on their original function and position in the skin. References. (note: illustrations that accompanied the talk are not included).