STRUCTURE OF HUMAN SCALP HAIR−II 29 with the small granules (0.5–1 μm in diameter) which was strongly stainable with the protein-specifi c dyes such as Coomassie Brilliant Blue (CBB) and gentian violet see Figure 9. By contrast, the tube of elderly persons was sparsely populated with the vesicles and some of the vesicles were loosely packed with the granules as typically seen in Figure 9B. It would be worth noting here that the hairs of a baby or an infant were generally very thin and Figure 9. (A and B) The drum-shaped ve sicles in the M tube (A and B) were pictured using the black hair (cf16) and the white hair (jm67), respectively. (C) The amorphous cluster of the granules which came ou from the vesicles of the white hair (jf65). The hair samples (3–5 mm length) were warmed at 30°C in a pH 7/PBS solution of papain (about 20 units) for 3–5 h, then in the fresh enzyme solution for another 30 min. The digested hair fi bers were randomly cut by means of the rapidly rotating poly(ethylene) cutter, and then centrifuged to collect the hair fragments Giemsa staining.

JOURNAL OF COSMETIC SCIENCE 30 the M was premature or not well developed thereby, the inner part of their fi bers, which was surrounded by the cuticular region, often appears to be packed homoge- neously with the cortical cells. Accordingly, the overall look of the human hairs varies from sample to sample, especially with age and race, and has indeed been interpreted variously (13,14). MATERIAL FLOW PROPERTY OF THE MEDULLA The cuticular cell region of the human hair functions to protect the fi ber against foreign substances and physical shocks such as heat action and mechanical friction. The cortical cell region is deformable, making it possible for hair to take an eccentric cross section and have a wavy line-shape (11,16). Although the biological function of the medulla has not been well understood, the hair component was characterized by the tubular structure as explained previously. Hence, we further investigated the possibility of the material fl ow through the Asian hairs to obtain the following results. (i) The relatively large molecules such as bromocresol green (BG), Congo red, and phe- nolphthalein were very diffi cult to penetrate the cuticular cell region cf. Figure 1. The dye molecules, however, entered the hair fi ber from the medulla ends. For instance, BG traveled about 30 μm (about one-third of the hair width) in 30 min at ambient temperature from the terminal of the fi ber (jm67) as typically demonstrated in Figure 10. (ii) The cuticular cell region worked well as a barrier for intrusion of even small ions into the hair fi ber. In other word, H+ ions and OH- ions were capable of migrating preferentially through the medulla tube as displayed in Figure 11A–C and D and E, using Congo red and phenolphthalein as pH-indicators, respectively. The aforementioned barrier property of the cuticular cell region may be rationalized by the presence of CuP—the large homo- geneous layer which encircles the fi ber shaft (1) see Figure 1. (iii) The conduit property Figure 10. The slow penetration of BG in to a hair fi ber through the cuticular layer and the fast intrusion of the dye into the fi ber from the M end. The white hair fi bers (jm67) were fi rst warmed in a mixture of 8 M urea and 4 wt.% SDS at 55°C for 2 h, then dipped in 0.5% BG solution at ambient temperature for 30 min. After brief washing with water, the hair fi bers were examined with the upright microscope.