35(, JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 1.--A 64's wool fiber (Rambouillet), dyed with Janus Green B, viewed in polarized light (X 80). the two components of the cortex differ from each other in swelling in alkali, and in birefringence after exposure to alkali and that they appear to be in the form of hemicylinders wound round each other helically in phase with the fiber crimp, so that one component is always placed at the outer side of the crimp curvature, with the other component at the inner side. In 1938 in Japan, Ohara demonstrated the differential dyeing effect on fibers dyed both in bulk and as cross sections with basic dyes (10). He pointed out that in the case of a basic dye, such as Janus Green B, the convex outer portion of the crimp curvature is preferentially stained. He appears to have had limited success with acid dyes in this regard, but did claim that Orange G preferentially stained the concave inner side of the crimp curvature in some experiments. In 1939, Ohara also published observations that these concave inner portions exhibit the greater bire- fringence (11). The later work of Horio and Kondo in 1953, referred to previously (7), confirmed the findings of Ohara that the differential dyeing effect may be observed on fibers dyed both in bulk and as cross sections and that a basic dye, such as Janus Green B, preferentially dyes the convex outer portion of the crimp curvature. These workers also reported that the acid dyes, Orange G and Ponceau 2R, preferentially stain the concave inner portions of the crimped fibers. Their views appear to have been shared by Mercer who in his 1953 paper (8) named the portion of the fiber more heavily dyed with basic dyes the "orthocortex." He demonstrated that this portion could be removed preferentially from the remainder of the fiber by a process of supercontraction and subsequent digestion with the enzyme trypsin. The remaining portion of the fiber cortex, which was named the "paracortex" by Mercer, is generally less reactive to chemical reagents. In Fig. 2, there appear two photomicrographs illustrating this effect. The procedure used

EFFECT OF BILATERAL STRUC• URE ON KERATIN FIBERS 357 .%. ':'• ...... .. er : .:,,. '2 (a) (g) Figure 2.--64's Rarnbouillet fibers treated with water at 120øC., followed by trypsin digestion (X 150) (a) viewed in normal light, (b) in polarized light. here was modified slightly from the original one of Mercer (8). A sample of short segments of some 64's wool fibers (U.S. Rambouillet) were super- contracted by exposure to superheated water at 120øC., over a period of four hours, using a pressure cooker. Following this, the supercontracted fibers were treated with the enzyme trypsin at pH 7 for a period of forty- eight hours. Figure 2a, a photomicrograph taken with ordinary light, shows how this process removed the orthocortex cleanly, leaving behind an epicuticle-plus-paracortex fraction. The photomicrograph of these same fiber segments, taken under polarized light (Fig. 2b), demonstrates how the remaining birefringence shown by the fibers is a property of the remain- ing paracortex. Independent experiments, done to determine the actual weight loss by this process, indicated that it was about 50 per cent of the fibers' initial weight. Mercer (8) as well as Horio and Kondo (7), called attention to the fact that this bilateral structure for the wool fiber may be an explanation of the experiments reported by Freney in 1947 (4). Freney found that fine wool fibers, when immersed in 1 per cent sodium hydroxide at room temperature (20øC.), showed a remarkable tendency to curl up and form tight coils. On the basis of the ortho-paracortex model it is possible to attribute this coiling to a greater sensitivity to alkali on the part of the orthocortex. The situation is analogous to that of a bimetallic strip used in a thermostat, where, because of a difference in the coefficients of thermal expansion of the two metals involved, the bimetallic strip curls when heated. In the case of the wool fiber, the curling comes about because of the dif- ference in the tendency to swell of the two halves of the cortex. The photomicrographs shown in Fig. 3 illustrate what happens when short lengths of wool fibers are exposed to alkali after a prior treatment with