Chapter 1 17 transverse cross-sectional area of each cell and approximately 75 % of the entire fiber section. They contain the so-called “keratin composite.” Macrofibrils are arranged longitudinally within each cortical cell and are packed close together with the intervention in places of an intermacrofibrillar matrix. In the late 1960s two different types of cortical cells were identified by this author in transverse sections of human hairs examined under the transmission electron microscope according to the amount of intermacrofibrillar matrix separating the macrofibrils.39 Cells defined as paracortex contained macrofibrils packed shoulder-to-shoulder with the intervention of almost no intermacrofibrillar matrix (Figure 9 left). By contrast orthocortex cells contained macrofibrils separated from each other by a significant amount of intermacrofibrillar matrix (Figure 9 right). Following from this an important relationship was discovered between the distribution of the two cell types in transverse hair sections and the degree of natural curliness of the Figure 8. Low power transmission electron micrograph of a transverse section of human hair stained with phosphotungstic acid.