JOURNAL OF COSMETIC SCIENCE 438 Three types of CMC have been described in the literature (8): cuticle–cuticle CMC, rep- resenting CMC between cuticle cells cortex–cortex CMC, representing CMC between cortical cells and cuticle–cortex CMC, representing CMC at the cuticle cortex boundary Figure 1. Rogers’ view of the CMC in 1959 (not drawn to scale). Figure 2. Schematic representing the cuticle–cuticle CMC. This schematic was fi rst modifi ed by Robbins et al. (4) from a schematic by Bryson et al. (5) of the cortex–cortex CMC and has been subsequently modifi ed into its current form (not drawn to scale). Figure 3. Schematic representing the cortex–cortex CMC.

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).