HAIR AND WOOL 775 is required in hair before disulfide-sulfhydryI interchange reaches sufficient proportions to have a significant effect on the mobility of the protein chains. 5. Diffusion of Reagents Human hair fibers have a larger diameter than most wools con- sequently, the penetration of a reagent to the core of the fiber would take longer even if its diffusion through the keratin substance were the same. In fact, for most large molecules, such as dyes, the diffusion is slower in hair. Data derived from measurement of uptake of a_n add dyestuff at 60 øC by several fibers are shown in Table II (7). The half-dyeing time, which is affected by both the fiber diameter and the diffusion coefficient, is 25 times longer for hair than for wool. Table V Axnino Acid Contents (Micromoles/g} Type of Side Chain and Amino Acid Lincoln Wool Caucasian Hair Negro Hair .4 liphatic 2830 2350 2470 Glycine 590 589 541 Alaninc 601 471 ,509 Valine 570 538 568 Leucine 740 554 670 Isoleucine 883 250 277 Aliphatic Hydroxyl 1020 I520 1290 Serine 541 870 672 Threonine 483 653 615 A romatic 540 260 380 Tyrosine 266 I32 202 Phenylalanine 273 130 179 .4 cidic 1400 1330 1350 Aspartic Acid 575 455 436 Glutamic Acid 828 871 915 Basic 1040 790 $00 Lysine 310 213 231 Arginine 662 512 482 Histidinc 71 63 84 ,¾ulf ur Containing 750 I440 J 384t Half-Cystine 745 1380 1370 Cysteic Acid 6 55 10 Methionine 0 0 0 Heterocyclic Proline 490 672 662 A mmonia .l 030 780 985

776 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 4• i i i i • LINCOLN WOOL Menkart and Speakman, 1947 • 30 • • HAIR • 10 • O.IM Hg[OAc]•in O.IN HOAC, 22•C • I I I 0 20 40 60 80 100 120 TREATMEHT TIME, HOURS lOO 2o HAIR MERINO•••, Dusenbury and Menkart, 1955 4 • 12 1• 2'0 24 TIME IN BOLLING O-04N H2 SOd, HOURS Figure ,5. Alkali insolubility as a function of time in boiling 0.04 W H•$O4 (10) All four specimens of human hair have very similar diffusion co- efficients. Those of both wools are higher: one slightly so, the other substantially. The phenomenon has also been examined for the action of mercuric acetate on human hair and Lincoln wool, as measured by the increase in work required to stretch the fibers as shown in Fig. 4 (29). The