JOURNAL OF COSMETIC SCIENCE 446 the fi bers by electron microscopy after each stage of treatment. After the initial solvent ex- traction, the cuticle–cortex CMC appeared unmodifi ed, while the staining intensity of the beta layers between cortical cells were changed and appeared “intermittent.” After solvent extraction for fi ve hours and hydrolysis for 15 minutes, signifi cant structural changes were observed. The cortex–cortex CMC showed an overall reduction in defi nition in the delta layer, and the beta layers displayed a lack of clear defi nition. These scientists suggested that solvent extraction of intercellular lipids makes the hair more vulnerable to hydrolytic dam- age, with the largest changes in the CMC occurring in the cortex–cortex CMC, which these scientists believe is related to a reduction in tear strength of wool fi ber by solvent extraction and hydrolysis. These results show that the cuticle–cortex CMC behaves differently from the cortex–cortex CMC in reaction to solvent extraction. The cuticle–cortex CMC is damaged by solvent extraction and subsequent hydrolysis, but not as severely as the cortex–cortex CMC. Logan et al., in 1990 (38), examined wool fi bers by TEM after extraction with chloro- form/methanol and found that the cuticle–cuticle CMC appeared unchanged compared to untreated fi bers. On the other hand, they found that the delta layer in the cortex was smaller and displayed variable staining intensity in most regions, which they deduced as “incomplete or preferential extraction.” These scientists examined fi ber sections after chloroform/methanol extraction, followed by treatment with formic acid, and noted large changes in the beta and delta layers of the cortex–cortex CMC that were “rarely observed” in the cuticle–cuticle CMC. They concluded that these results show that “inherent differ- ences exist between CMC’s of cuticle and those of cortical cells.” Negri et al. (39) in a 1996 paper referred to the work of Leeder et al. (50) and cited the work of Leeder, Bishop, and Jones (44), who showed that the unstained beta layers of the cuticle and cortex react differently to formic acid treatment. Formic acid removes pro- teins (51) from the cortex–cortex CMC (40), and it modifi es the CMC junctions of the cortex but not the cuticle–cuticle CMC junctions they referenced Nakamura (8), Leeder, Bishop, and Jones (44), and Peters and Bradbury (49) on these effects. They concluded that these observations suggest that only the beta layers of the cuticle–cuticle CMC con- tain covalently bound lipids, while the beta layers of the cortex contain lipids and a “stain-resistant membrane protein” that is “likely to be of a different structure than the cuticle membrane.” Inoue et al. in 2007 (52), by microbeam X-ray diffraction described that extraction of human hair with polar organic solvents (methanol or chloroform/methanol) at 37 degrees C for six hours removed some material from the delta layer of the cuticle–cuticle CMC, but that the beta layers were unaffected. On the other hand, the beta layers of the cuticle– cuticle CMC appeared to be affected by hexane extraction under the same conditions. The observation that changes in the delta layer of the cuticle–cuticle CMC by chloroform/ methanol extraction could be detected suggests that this method is more sensitive than TEM (38). The fact that Inoue et al. observed changes in the beta layers of the cuticle– cuticle CMC by hexane extraction could result from removal of free lipids between the covalently bound fatty acids of the cuticle–cuticle CMC (Figure 2), resulting in the fold- ing back of the covalently bound fatty acids in the beta layers and accounting for the differences found. The above discussion shows clearly that both the lipid beta layers and the proteins of the cell membranes and those of the delta layer of the cuticle–cuticle CMC differ from those of the cortex–cortex CMC, with evidence for differences from the cuticle–cortex CMC also.

CELL MEMBRANE COMPLEX 447 A PROPOSAL FOR THE STRUCTURE OF THE CUTICLE–CORTEX CMC The following proposal for the cuticle–cortex CMC (Figure 7) is based on logic and the following supporting evidence. The work of Nakamura et al. (8) suggests that the cuticle– cortex CMC differs from both the cuticle–cuticle CMC and the cortex–cortex CMC. The work of Leeder et al. (44) and of Mansour and Jones (37) shows that the cuticle– cortex CMC is more resistant to solvents than the cortex–cortex CMC. But the most convincing evidence for this model (Figure 7) is the uranyl dye study by Leeder et al. (50) which showed layers of dye around each cuticle cell, i.e., two layers of dye in the cuticle– cuticle CMC, one layer of dye in the cuticle–cortex CMC, and no layers of dye in the cortex–cortex CMC. Since the cuticle–cortex CMC bridges cuticle and cortical cells, it is logical to assume that it is a hybrid based partly on the cuticle–cuticle CMC and the cortex–cortex CMC. Therefore, the membrane on the cuticle side would be the cuticle cell membrane that supports covalently bound fatty acids that are bonded either through thioester, ester, or amide linkages, and these covalently bound fatty acids are connected on their hydropho- bic end to a hydrophobic protein in the delta layer. The membrane on the cortex side is a cortical cell membrane that supports fatty acids bound through polar and salt linkages, as illustrated in the schematic of Figure 7, and these fatty acids form a lipid bilayer. The delta layer of the cuticle–cortex CMC should then contain a hydrophobic protein on one side (to bond to the beta layer on the cuticle side) and a hydrophilic protein on the opposite side (to bond through polar and salt link- ages to the lipid bilayer). Leeder et al. (50) in their TEM study on dyeing and diffusion suggested that either the cuticle beta layer or the resistant membrane surrounding cuticle cells has an affi nity for the uranyl dye, whereas the cortical cell membrane or the delta layer between cortical cells does not. The models in Figure 7 (for the cuticle–cortex CMC), Figure 2 (for the cuticle–cuticle CMC), and Figure 3 (for the cortex–cortex CMC) are consistent with the results and explanation by Leeder et al. (50) of the uranyl dye binding in the three different CMCs. Figure 7. Schematic representing the cuticle–cortex CMC (not drawn to scale).