STRUCTURE OF HUMAN SCALP HAIR−II 31 of the medulla was assisted electrically. In other words, the aqueous solution of the cationic anthocyanine dye easily fl owed through the medulla in a direction from a positive electrode to a minus electrode when more than DC 500 voltage was applied between the tip and the root positions of a white hair fi ber (jm67) see Figures 3 and 12. As expected, (i) the dye-fl ow was completely blocked and hence the medulla was not stained at all when either one of the fi ber ends was capped with gelatin, and (ii) the fl ow was directionally reversed with the polarity of the electrodes interchanged see Figure 12 (1–3 min vs. 3 min 40 s–5 min). Furthermore, the hair shaft itself (80 μm in diameter and 20–25% water content) showed a very high resistance of about 109 ohms/cm when the both ends Figure 11. (A–C) The H+ ion-fl ow through t he M of the black hair fi ber (jf8) at 25°C bar 100 μm. The fi ber was thoroughly stained with Congo red, then its left end was acidifi ed by 0.5 M HCl see the pro- cedure “H+ ion-fl ow through the M: The use of Congo red as an indicator” for more details. The time-lapse after acidifi cation is printed in each picture. The M changed gradually in color from gray to reddish black toward the right hand side, as indicated by the arrow. The M tube was isotropic to the fl ow of H+ ions. (D and E) The OH- ion-fl ow through the M at 25°C bar 100 μm. The white hair fi bers (jm67) were stained by an aqueous solution of phenolphthalein, and then one of the two ends was alkalifi ed by 1 M NaOH cf. the procedure “OH--fl ow through the M: the use of phenolphthalein as an indicator” of the experimental section. The color change (to red) occurred only in the M, taking less than 10 min to extend to the other end.

JOURNAL OF COSMETIC SCIENCE 32 Figure 12. The DC voltage-assisted fl ow of the purple an thocyanin dye through the M cf. Figure 3. One strand of the white hair (jm67) was put through the glass capillary, making one end dip into the dye solution and the other end into PBS. DC 550 voltage was then applied between the electrodes. See the procedure “Flow of the anthocyanin dye through M: Application of a DC voltage to a hair shaft” for more details. The time-lapse after application of the voltage is indicated in each of the panels. Panels of 1 and 3 min: When the buffer solution-bath was set as a minus electric side (cathode), the cationic purple dye fl owed through the M, causing the length and color-density of the purple band within the M to increase with increasing time of the voltage application. Panels of 3 min 40 s and 5 min: When the polarity of the electrodes was reversed, the dye fl owed back to the PBS bath to result in diminishing the purple color density in the M. The observed direct current was 23 ± 2 μA in this case. of the hair fi ber were not touching the electrode solutions. All of the aforementioned fl ow experiments may be taken to suggest that the medulla functions as a channel, at least in the early growing stage of the hair. The biological functions of the medulla have been under further study. CONCLUSIONS The medulla (M) of the Asian scalp hairs is mainly composed of the primary and secondary M-surrounding cells. The medulla is featured in its large tubular architecture (diameter, 20–30 μm). The drum-shaped vesicles, which contain many small proteinous granules, are embodied inside the tube. Various kinds of substances such as H+-ions and dye mol- ecules are able to fl ow into the hair fi bers through the tube.