A Method of Isolation of a Cuticle Sheath from Wool Fibres

Previous work on the wool fibre has resulted in the isolation of two membranous components, viz. the epicuticle and the cortical cell membranes, and the postulation of the presence of a third membrane, viz. the subcutiole membrane, or endocuticle. The present work describes the isolation from the wool fibre of a cuticular sheath, which has been shown to consist of epicuticle and endocuticle. The method described employs oxidation with potassium dichromate followed by extraction with ammonia. The material resistant to this treatment was examined in the optical microscope, and its morphological significance was confirmed by electron‐microscopic studies of gold‐shadowed residues. Electron microscopy also revealed a fibrillar and microfibrillar structure of the endocuticle, thus explaining the grooved appearance of the surface of damaged wool fibres (e.g. after wet chlorination). The sulphur content of the dichromate‐ ammoniaresistant endocuticle (comprising at most 2% of the original wool) is shown to be appreciably higher than that of the complete wool fibre. This sulphur is shown to be present in the form of cystine, but the resistance of the cystine in the cuticular layer to dichromate oxidation is unexplained.