A transmission electron microscope study has shown that an unstained layer, thought to contain covalently bound fatty acids, completely surrounds the cuticle cells of wool fibers. Alcoholic alkali and chlorine treatments, which both release covalently bound fatty acids, result in the disappearance of the unstained layer. This layer is thought to be an integral part of the cuticle cell membrane. Similar unstained layers between cortical cells are different from the unstained cuticle membrane, because they remain unmodified by alcoholic alkali treatments.Recent studies have provided evidence that wool fibers contain a layer of fatty acids covalently bound to the surface of the cuticle cells, probably by a thioester linkage [ 2,7,13,15,16,21 ] . These acids are orientated to produce a &dquo;polyethylene-like&dquo; hydrophobic layer at the fiber surface [20]. A feature of the fatty acid distributions of the surface lipids of wool and many other keratinous fibers is the presence of a large amount of an unusual, branched chain fatty acid, 18-methyleicosanoic acid [ 13,16 ] .Keratin fibers such as wool and human hair consist of elongated spindle-shaped cortical cells packed into the cylindrical. core of the fiber (known as the cortex), which is surrounded by an overlapping sheath of flattened cuticle cells [ 10 ] . The intercellular spaces have been termed the cell membrane complex, which under the transmission electron microscope appears as an intensely stained region (the 6-layer) sandwiched between a pair of unstained layers (the @-layers) [4]. The @-layers are thought to largely contain lipids and to originate from the follicle cell plasma membranes, whereas the 5-layer is believed to consist primarily of protein, deposited in the intercellular spaces during keratinization [4,10].In this study, we have examined the unstained fjlayers in wool fibers, and in particular those associated with the cuticle cells using transmission electron microscopy, following a variety of alcoholic alkali and chlorine treatments. These treatments are known to release various levels of covakntly bound fatty acids from the fiber, depending on the treatment conditions [ 13,15 ] . Changes observed in the unstained layers of cuticle cells after treatment indicate that oovakntly bound fatty acids are an integral part of the /3-layer surrounding cuticle cells. Materials and MethodIn this study, we used Merino woois ( 16 or 22 cm diameter), obtained by cutting butt portions (about two-thirds of the length) from fleece staples and cleaned by two alternative procedures. The 16 11m Merino wool was cleaned by drying in a vacuum oven for 24 hours at 50*C, Soxhlet extracted with t-butanol for 5 hours, followed by isooctane for 3 hours, then rinsing in distilled water for 6 hours [ 15 ] . The 22 11m Merino wool was cleaned after the method of Leeder and Marshal[6], in which vacuum dried wool was sequentially extracted with dry t-butanol, heptane, rinsed extensively with distilled water, rodried, and then sonicated for 3 hours with dry heptane. Both pr...