444 JOURNAL OF COSMETIC SCIENCE medulla.. •- i• bqir fiber A B 340 nm MF MF C .. Figure 3. Photomicrographs of virgin dark brown hair showing the medulla in different views. A: Hair fiber seen under reflected light in the stereomicroscope at 660x. B: Hair fiber seen under transmitted light in the stereomicroscope at 660x. The arrow points to the continuous medulla placed in the middle of the hair fiber. C: Transmission electron micrograph of virgin dark-brown hair fiber (Elmiskop101 at 80 kV, osmium-stained) showing the cortex region. Note the non-fibrillate constitution of the medulla (M), which is surrounded by the macrofibrills (MF).

EFFECT OF DYEING AND HEAT ON HAIR COLOR 445 A c ß . discontinue medulla Fig 4. Photomicrographs of virgin dark-brown hair submitted to dryer heat (final magnification 480x, bright-field and transmitted light). A,B: Fibers after 50 min of heat exposure. C,D: Fibers after 110 min of heat exposure. Note that the medulla disappears progressively with dryer heat exposure.

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