230 KERATIN AND KERATINIZATION 



Frederic (1943) of a high concentration of SH groups in the granules. On 

 the other hand, most other observers seem to agree that there is little or no 

 sulphydril or disulphide in the granules (Van Scott and Flesch, 1954; 

 Montagna, 1956; Eisen et al.). 



The present writer (Mercer, 1958) has supported the view that the 

 keratohyalin granules are a direct precursor of the fibrous keratin and that 

 something of the same type of transformation occurs as was found in the 

 Henle layer of the inner root sheath of the hair follicle (see Plate 22). 

 Images showing filaments apparently emerging from granules may be 

 found. The amounts of fibrillar material in the cell of the granular layer also 

 appear to be too small to provide the amounts visible in the immediately 

 adjacent cells of the stratum corneum. Thus it seems that this material can 

 come only from the accumulated granules. A conversion of the granules 

 into fibrils running roughly parallel to the skin in the flattened cells could 

 account for the sudden rise in birefringence (with its positive axis parallel 

 to the skin) and for the glassy appearance of these layers {stratum lucidum) 

 which stongly resembles Henle's layer above the transformation level. It 

 would seem that here the two potentialities of synthesis of the basal 

 epidermal cells, which become separated into two distinct cell lines (the 

 cortex and the i.r.s.) in the hair follicle, occur together in the epidermal cell 

 but manifest themselves at different times and levels. 



Thus (in this view) the final fibrillar contents of the cells of the stratum 

 corneum would seem to be derived from two sources: (a) a small early 

 contribution of fibrils analogous to the cortical filaments of hair and 

 appearing like them without a precursor, and (b) a larger amount produced 

 later by the transformation of the non-fibrous precursor, keratohyalin. 

 The relation of these two kinds of fibrils to each other and the reasons why 

 the cells switch from one form of production to another are not known. 



When in the fibrous form, trichohyalin yields an a-type X-ray pattern 

 and its sulphur content is low (Rogers, 1959a). These findings also apply 

 to the keratohyalin of skin, if we accept the claims that the granules contain 

 little or no S. Amounts of SH and disulphide are demonstrable in the 

 cytoplasm of epidermal cells at all levels with a stronger band near the 

 clear layer. Van Scott and Flesch (1954) report that there is little increase 

 in the total S in passing from the germinal to the horny layer which might 

 agree with the picture presented above if we assume that the earlier formed 

 fibrils become stabilized by disulphide cross-linking but that keratohyalin 

 on forming fibrils contributes little further disulphide. By measuring the 

 specific absorption of X-rays, Engstrom and Lindstrom (1947) showed that 

 the concentration (S per cm 3 ) was many times higher in the stratum 

 corneum. This increase is undoubtedly largely due to cell dessication but 

 may also indicate an absolute increase in S content. 



Rothman (1954) has proposed the idea that the cell inclusions may 



