The Structure and Chemistry of Human Hair 14 effete nuclear chromatin of the cuticle cell. With longer term trypsin digestion or short-term pronase digestion, this produced large holes in a discrete region of each cell seemingly coincident with the region of the smaller holes produced by short term trypsin digestion.29 There was little doubt the larger holes had occurred in the region of each cuticle cell containing the effete cell nucleus. This effete nucleus will have been compressed into a discus-like structure occupying the central region of each endocuticle sheet. It is otherwise not easy to identify in electron microscope sections of the cuticle, but it is pertinent to mention such a structure has been seen in each cuticle cell under the light microscope.32 All the components of the endocuticle, including the effete nuclear remnants, are rapidly removed by pronase treatment. Analysis of the dissolved material reveals relatively large amounts of hydrophilic amino acids are present.29 This, coupled with the absence of cystine as judged by the lack of staining with ammoniacal silver, undoubtedly makes the endocuticle susceptible to being swollen significantly in water as compared with lack of swelling in the other highly cross-linked laminae of the cuticle. Thus we see the contents of each cuticle cell are divided between tough outer laminae (A-layer and exocuticle) and a soft underlying lamina (endocuticle). Inner layer: As mentioned earlier this component is continuously applied on the inner-facing aspect of each cuticle cell adjacent to the cell membrane complex. Its thickness varies from 100 to 400 Å. Little is known about its chemical composition except that it is evidently rich in cystine and, like the epicuticle layer on the other side of the cell, is probably cross-linked by isodipeptide bonds. Whether fatty acids are covalently attached to it remains to be seen. Cuticle cell membrane complex (CMC): The internal structure of this component, that continuously and at relatively constant thickness separates cuticle cells one from another, is readily revealed in sections stained with phosphotungstic acid (PTA)(c.f. Figure 7). It is distinguished by a 180 Å-thick central lamina known as the δ-layer that stains strongly and is bounded on each side by so-called β-layers of between 25 and 40 Å-thickness that remain unstained.