358 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (a) (3) Figure 3.--64's Rambouillet fibers boiled in sulfuric acid solution ofpH 1.8 for 8 hours, then exposed to 2•/u% NaOH () 150) (a) viewed in normal light after 19 minutes' exposure to alkali, (b) viewed in polarized light after 20 minutes' exposure. sulfuric acid at the boil. It may be observed that the more swollen half of the fiber, the orthocortex, is on the inside of the curvature. Figure 3a was taken under ordinary light, whereas polarized light was used for Fig. 3b which shows the same fibers. Here it may be seen that the outer portion of the curved fibers, the paracortex, shows strong birefringence, indicating that the fiber structure has been maintained. On the other hand, the inner portion of the fibers, the orthocortex, shows scarcely any birefringence. DISCUSSION OF THE BILATERAL STRUCTURE OF APPAREL WOOL FIBERS* Another way in which the orthocortex differs from the paracortex is in its cystine content. In 1954, Mercer, Golden and Jeffries (9) found that the cystine content of the paracortex-plus-epicuticle fraction was appreci- ably higher than that of the whole wool fiber. Reasoning that the para- cortex constitutes about 50 per cent by weight of the whole fiber, they were able to calculate the per cent of cystine in the orthocortex. The ortho- cortex had been removed from the whole fiber by the method previously described: supercontraction with steam followed by enzymatic digestion. This finding suggests that a reason for the apparently greater resistance of the paracortex to chemical attack may be that it possesses a higher cystine content that is, it is a more highly cross-linked protein system. The finding of Ohara (10) and of Horio and Kondo (7) that the dif- ferential dyeing effect may be observed when dyeing follows cross section- * In view of recent work reported by Dusenbury and Coe (2) the portions of this paper dealing with the interpretation of differential-dyeing experiments and the amino add analyses of the fiber cortex have been extensively rewritten since the 1954 presentation at the Cosmetic Seminar.

EFFECT OF BILATERAL STRUCTURE ON KERATIN FIBERS 359 ing, as well as when dyeing precedes cross sectioning, is an extremely important one. This finding has also been confirmed by work at Textile Research Institute. It shows that differential dyeing is truly a property of the cortex and is not a result of differential diffusion of dye through the cuticle. In addition, if the orthocortex is dyed preferentially by a basic dye and the paracortex is dyed preferentially by an acid dye, it must be inferred that the dyeing results represent an equilibrium phenomenon, with the orthocortex containing an excess of sites for basic dyestuff cation and the paracortex containing an excess of sites for acid dye anions. Such a view would appear to be confirmed by the amino acid analyses of several wool fractions by Golden, Whirwell and Mercer (5). Using a paper chromatographic technique, these workers carried out amino acid analyses of the whole wool fiber (Australian Merino) and of the paracortex- plus-epicuticle fraction which was prepared by the procedure of super- contraction followed by enzymatic digestion. The paracortex in com- parison with the orthocortex was found to contain larger quantities of a diabasic amino acid, such as arginine, and smaller quantities of dicarboxylic amino acids, such as aspartic acid and glutamic acid. The paracortex was also found to contain about twice the cystine content calculated for the orthocortex. Since it is possible to prepare cross sections prior to dyeing, a key experf- ment suggested itself as a logical way to test the idea that the orthocortex N preferentially dyed by basic dyes and the paracortex is preferentially dyed by acid dyes. This experiment is to prepare a section, dye it with a basic dye, and then attempt to prepare the next section a few microns ß ....• .:. •.?' '.5:, '":4' • -... : . •:?.... •. •.:• . ... •:... •. . '".: .• '• .... •::.: .... 5. "•:"'.',. ß5:-•'-' ...? • . .. : .•. ..• ß . :.. ß .- ,•.• .--.:... .• -'..=:. . :•:- .::... :•.:: ß .. -5• '.':'.• • • .- •.:•:.75 g .. -' (•) .•...' .'•, •75.":".•'•-....•:•-•7%:.•:•:•:5•.:,•.:'.'..''*?".-' • • ..... •':: '%' "% ' ' ß - :...'. '• '"• •" "•"'• "' :,- •' •'." "' "-75.• • "..'•.. •--• .•:.'•.i•5•..:• •..: •. .• . •:::•.•..:-.:%:-.:.. •? ' •:•:•%. "•- ::•'• •. • '•'•: ,. •5•: ":'"' '•5 •.'5:,: :...5 .:. ß •: . •:5 •... ,-..= •:..• •... .v ? •.• ß .g.:• . •,. •.•: :.•- i• .... :.... •-%5 -:. •.. :-) •.• :. :.•--,-.• ....•.•. .?•' •.: :•.i..........-•{ . ,•e.- ..• ..... rc:-• •-• • ' :• • ...:..-• :./•-...•:•'.'.•:.•-. ....... '• ....•....%'•.•-.,.. ¾? .•:. •'•.•....• . ß • • -'..• .' •.... 5, o.' .... ß .... • .- .... •.•...:.•.-::•.: • "'i. • -.•- .. . .... •.•. •.. '5.::. • 5.• .: . .'i i= .•. '• "•:•::i:•..•.' '•5' ' ::'•': '•:?' ::' ..ge•, ß '•?:." .. •'•'• :'•'.•":""i %• ß ' '¾%:1 •:-• •.:'.='.5: ::.•'•.•' .,• •' •. Figure 4.--Photomicrographs of successive sections of 64's Rambouillet fibers (X 660) (a) dyed with a basic dye, Janus Green B (C.I. 133), (b) dyed with an acid dye, Formyl Violet S4B (C.I. 698).