Structure Of Wool Fibers Research Articles

Microscopic structure of the wool fiber

An investigation was undertaken to obtain information con cerning the fine details of structure of wool fibers and especially of their constituent scale and cortical cells. Treatment of chemi cally...

Microscopic Structure of the Wool Fiber

An investigation was undertaken to obtain information con cerning the fine details of structure of wool fibers and especially of their constituent scale and cortical cells. Treatment of chemi cally modified wool with the enzyme, pepsin, was found to be an excellent method for releasing individual cells for such studies. It is shown by microdissection that the striated appearance of the cortical cells is due to the presence of many fibrils which can be separated with microneedles. Near the center of each cell is a nucleus which has a granular structure. Between crossed nicols, the fibrillar part of the cortical cells appears birefringent, whereas the nucleus does not. The scales show little internal organization such as exhibited by the cortical cells. When examined with crossed nicols they appear nonbirefringent. Unlike the cells of the cortex, the scales are not easily separated by treatment with enzymes, but remain attached to each other in a manner comparable to the arrangement of shingles on a roof. A comparison of root and shaft of the fiber reveals numerous differences in reaction to microchemical color tests, as well as differences in cellular structure. The root, for example, gives a positive test for sulfhydryl groups whereas the shaft gives a nega tive test. Similarly, the shaft appears birefringent whereas the root does not. These and other observations clearly indicate that as the cells of the root emerge into the shaft a number of physical and chemical changes take place simultaneously. When wool is placed in chlorine water bubbles arise on the surface of the fibers (Allwörden reaction). Evidence is presented in support of the viewpoint that these bubbles arise solely from the scales and that their formation is associated with the reaction of the chlorine with disulfide groups of the cystine in the scales.

Examination of the fine structure of wool by X-ray analysis

During recent years an exhaustive study has been made of the elastic properties of wool fibres under widely different conditions of temperature and relative humidity. It has been shown (1) that the elastic properties of the fibre as a whole are those of the single cell, which consists essentially of an elastic cell-wall enclosing a fibrillar structure, which is not haphazard but is usually disposed along the axis of the fibre. The enveloping cell-wall remains perfectly elastic up to 70 per cent. extension in water at ordinary temperature but the fibrillar structure under similar conditions is plastic. Extended fibres may undergo permanent alteration either by rupture or by plastic flow of fibrillæ, but invariably retain their ability always to return to their original length in water at ordinary temperatures, on account of the perfect elasticity of the enclosing cell-wall. The plasticity of the fibrillar structure, which is so marked in water at ordinary temperatures, is scarcely measurable in atmosphere below 75 per cent. relative humidity. Such information regarding the structure of wool fibres has been derived almost entirely from a study of their stress-strain relationships, and it was considered that the validity of the general theory should be examined by a totally different method. An examination of the fine structure of wool fibres by X-ray analysis should disclose structure within the cell and its variation under changing conditions of stress and humidity.