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Accurate measurement of the relative areas of ortho- and paracortex segments in wool depends upon a suitable embedding technique which will allow proper cross-sectioning of dyed or undyed fibers and upon a dyeing procedure which will give optimum differentiation. A method of embedding is described in which fiber bundles are mounted in a gelatin capsule and embedded with butyl methacrylate, which has excellent hardness and sectioning properties. Differential dyeing is obtained with Methylene Blue for 40 sec at the boil or for 20 min in the cold, for either sections or whole fibers, in a buffer medium.

The percentage paracortex by area in well-grown, unweathered, high- and low-crimp wools has been estimated on cross sections dyed with methylene blue. The cystine/cysteine content of these wools was also determined. The high-crimp wools were found to have a higher percentage paracortex and sulfur content than the low-crimp wools. This is probably related to the speed of mitotic activity of the germinal layer of the bulb. If proliferation activity is high (faster growth) less sulfur is incorporated into the fiber. In this way cross-linking is reduced, resulting in less structural strain, which expresses itself in fewer crimps.