This review article will interest those concerned with the structure and properties of wool fibers. The cell membrane complex (CMC) is the material holding together the cuticle (scales) and cortical cells. Although it constitutes a small portion of wool and hair fibers it has a major effect on mechanical and chemical properties. It is the weak link in wool. The discussion of mechanical and chemical breakdown of wool via the CMC is excellent. Attack by microorganisms is included. Excellent photomicrographs and line drawings. -- AATA