Chapter 1 21 other in the orthocortex than in the paracortex. This is confirmed by transmission electron microscope observations of the relative orientations of KIFs in orthocortex and paracortex.41 In other words, in images of transverse sections of hairs one finds larger areas with discrete end-on KIF “dots” in the macrofibrils of the paracortex, whereas macrofibrils of the orthocortex are more like thumbprints. Full details of the orientation of KIFs in hairs of different degrees of curliness have been provided by Bryson and others in New Zealand.40 They examined thick transverse sections of metal- stained hairs in a high voltage transmission electron microscope and used a tomographic 3-D reconstruction method to discover the orientation of KIFs in the sections. Four different types of cortical cells were described by them type A of orthocortical character type B intermediate between orthocortex and paracortex (the so-called mesocortex first identified by Kaplin46) type C, of paracortical character and type D, a minor cell type usually found adjacent to the C-type cells. The orientation of the KIFs in the macrofibrils of the type A (orthocortical) cells on the convex side of each fiber were similar to those found in the orthocortex of sheep’s wool.50 That is the angle of tilt of the KIFs increased with radial distance from the center of each macrofibril. By analogy the situation is like that of a cylinder of parallel rods in which the cylinder has been twisted about its ends. Thereby KIFs out from the center of the cylinder present a helical path along the length of each macrofibril. In contrast to this, type B and C cells (paracortex and mesocortex, respectively) found on the concave side of each fiber possessed KIFs in greater parallel alignment in the macrofibrils than those of the A-type cells. In some macrofibrils the KIFs were tilted tangentially rather than radially, with the tilt angle increasing from the center of each macrofibril. Structure and composition of intermediate filaments of hair: Proteins are linear polymers of amino acids linked one to another as amides (otherwise known as peptide bonds). There are 20 different amino acids (c.f. Table 2) and it is the sequence of these in each protein that determines its conformational characteristics. In the