EFFECT OF BILATERAL STRUCTURE ON KERATIN FIBERS 365 acid or basic dyestuffs. Dyeings carried out on cross sections show that the kid mohair appears to be stained more readily by a basic dye than does human hair and that similar behavior is observed when acid dyestuffs are used. These conclusions are based on examination of dyed cross sections wherein mohair and human hair were mounted in the same slide, and dyeins occurred after cross sectioning. This would appear to indicate that mohair is more like an orthocortex fiber whereas human hair is more like a paracortex fiber. As another indicator of ortho-paracortex behavior, the cystinc contents of these fibers were investigated with the results shown below in Table 1. For comparison purposes, previous measurements are shown for whole wool fibers and for the paracortex fractions (including epicuticle) obtained by the supercontraction and trypsin digestion procedure ($). The cystinc contents shown were all determined by a modified Folin procedure, which measures cystinc plus any amounts of cysteine (relatively small) that might have been in the fibers prior to the determination. The orthocortex cystinc values were calculated on the assumption of a 50-50 division of the cortex between its two fractions. TABLE 1--CYSTINE CONTENTS OF SEVERAL KERATIN FIBERS Fiber Type Cystinc (Wt.%)* 64's wool: This work--whole fiber 11.4 4- 1.1 Previous work--whole fiber 11.6 4- 0.3 Paracortex (found) 14.9 -4- 1.0 OrlShocortex (calculated) 8.3 B. A. fleece wool 11.6 4- i i• Kid mohair 9.5 + 0.6 Human hair 16.7 + 0.9 * Values shown are means of four determinations with corresponding deviations of the mean values at the 95% confidence level. In view of the previous work on these fibers, these results are interesting. They imply that high cystinc contents (15 per cent or more) are associated with paracortex fibers, that low cystinc contents (ca 9 per cent) may be associated with orthocortex fibers, and that intermediate cystinc contents (11-12 per cent) may be associated with fibers having both ortho- and paracortex fractions. As another method for determining the ortho-para character of keratin fibers, the previous experimental results should be recalled for apparel wool fibers taken from acid-treated fabrics. From these experiments, a plot of alkali insolubility versus time of exposure to sulfuric acid showed a pro- nounced elbow in the curve (Fig. 5). This was taken to indicate that the initial, steep portion of the curve corresponded to a more rapid removal of chiefly orthocortex followed by a slower removal of the remaining para-

366 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS cortex. Accordingly, it was decided to do similar measurements on the other types of keratin fibers. The previous experiments described were carried out on the wool in fabric form and the alkali-solubility values were obtained on short pieces of yarn taken from the fabric. In the series of experiments to be described, a similar series of acid treatments was carried i00 g,,. 90 80 70 uman Hair 60 30 I0- 9 - 8 - 7 I 0 Rambouillet64's Wool Kid Mohair I t I • I • I t I t I 4 8 12 16 20 24 TIME OF EXPOSURE TO ACID (Hours) Figure 7.--Alkali insolubility of different keratin fibers boiled in sul- furic acid solution for varying times,