CELL MEMBRANE COMPLEX 439 (see Figure 4). Since Rogers’ (1,2) initial description of the CMC and his additional work demonstrating that the delta layer of the cortex consists of fi ve sub-layers (9), several additional important developments have occurred that will be described in this paper, adding new details to this important structure in animal hairs. SUPPORT FOR CUTICLE–CUTICLE CMC AND CORTEX–CORTEX CMC STRUCTURES GENERAL DIFFERENCES FOR CUTICLE–CUTICLE CMC VS CORTEX–CORTEX CMC Jones and Rivett (10,11) provided evidence that the CMC of the cuticle contains 18-methyl eicosanoic acid (18-MEA) in its upper beta layer while the CMC of the cortex has virtually no 18-MEA. The facts strongly suggest that the CMC of the cuticle has monolayer lipids that are attached by covalent bonds (primarily thioester) (12,13), with some ester or amide linkages (13) to proteins of the cell membranes on one end, and by van der Waals attractive forces to proteins of the delta layer on the hydrophobic end of the fatty acids (Figure 2). On the other hand, the CMC between cortical cells consists of lipid bilayers that are not attached by covalent bonding to protein layers but are bound by salt linkages and polar bonding to the cortical cell membrane proteins on one side and similarly attached to the delta layer on the other side of the bilayer (see Figure 3). References and supporting facts for these conclusions are presented in the next sections of this paper. CUTICLE–CUTICLE CMC In 1916, Allworden (14) discovered that chlorine water reacts with the cuticle cells of wool fi ber to produce large bulbous sacs on the fi ber surface. Chlorine water degrades proteins beneath the cuticle cell membranes (most likely cleaving disulfi de linkages be- tween the epicuticle and the A-layer (15)), producing water-soluble species too large to Figure 4. Location of the three different types of CMC (not drawn to scale).

JOURNAL OF COSMETIC SCIENCE 440 diffuse out of the semipermeable cuticle cell membrane. Swelling results from osmotic forces, and the cuticle membrane stretches, producing the so-called Allworden sacs that separate from the underlying proteinaceous intracellular matter. The epicuticle membrane was fi rst isolated and named by Lindberg et al. in 1949 (16,17). Several years later, in 1968, Leeder and Bradbury (18) defi ned the epicuticle as the “thin outer membrane which is raised on the surface of fi bers as sacs by treatment with chlorine water” in the Allworden reaction. The epicuticle provides the protein supporting struc- ture for 18-MEA in cuticle cells (see Figures 2 and 5). It is also attached to the A-layer of cuticle cells of wool and human hair, and together with 18-MEA is perhaps the most thoroughly studied part of the CMC. Leeder and Rippon (19), in 1985, suggested that the epicuticle was proteinaceous and covered with a strongly bound lipid layer that could not be removed by lipid solvents, but could be removed with alcoholic alkali they called this lipid layer the F-layer (see Figures 5 and 6). The F-layer of covalently bound fatty acids, together with the cuticle cell membranes (es- sentially the epicuticle), is analogous to the cornifi ed envelopes or the cellular envelope of Figure 5. Schematic of the hair surface showing the lipid layer (F-layer) and the cell membranes (not drawn to scale). Figure 6. Schematic of a transverse section of a cuticle cell with the CMC (not drawn to scale).