IV. The Molecular Structure And Elastic Properties Of The Biological Cells
Amongst the difficulties encountered in the study of the structure of hair not the least is its heterogeneity, whether considered crystallographically or histologically. From the former viewpoint progress has been made possible by assuming that there is no clear demarcation between “crystalline” and “amorphous” keratin, but rather that there is a continuous gradation of organization, so that the properties of “crystalline” keratin, which lies at one end of the scale, may be linked by a series of almost imperceptible changes with those of the keratin of any other degree of regularity. The X-ray photographs of the better organized parts have been regarded as signposts pointing the way to an understanding of what is happening, in the molecular sense, in the rest of the fibre substance. Histologically, it is possible to define to a certain extent the part played by the various structural elements by comparing the properties of different types of hair. In this way we find that all hairs have certain basic similarities in their behaviour, and if we confine our attention to these we may at once eliminate, as being of no fundamental importance, such special histological features as the cuticle or the medulla, which occur in certain types of hair only, or can be removed from the specimen. There remains, as the seat of the characteristic properties of keratin fibres, only the cortex, which in all hairs consists of a mass of biological cells apparently fused together by an “intercellular medium”. The present work is an attempt to discriminate between the cortical cells and the intercellular material in their relation to the elastic behaviour of the fibre.