1. Roberts, A. D., and Tabor, D., Nature, 219, 1122 (1968).
2. Roberts, A. D., and Tabor, D., Disc. Faraday Soc. (in the press).
3. Roberts, A. D., Eng. Materials Design, 11, 579 (1968).
4. Wright, V. (ed.), Lubrication and Wear in Joints (Sector, London, 1969).
5. Charnley, J., Proc. Symp. Biomechanics, London (Inst. Mech. Eng., 1959).