220 KERATIN AND KERATINIZATION 



The disappearance of the nucleic acid from the keratinized hair poses 

 some problems. A nuclear residue persists (see p. 263) but is not Feulgen- 

 positive. It would seem that, even in the upper levels of zone E where it 

 would be thought that the dehydrated and moribund cells would be 

 incapable of further activity, some reactions, which mobilize and remove 

 nucleic acids, can still take place. Perhaps this operation is of value in the 

 hair follicle in that valuable materials (phosphorus) are resorbed. Bolliger 

 and Gross (1952 and 1956) have, however, reported ample quantities of 

 nucleic acid breakdown products in hairs and other keratins. 



£^ 



K^=J 



c^ (F^ 



SH 



(a) (b) (c) (d) 



Fig. 97. The results of some histochemical tests on the human-hair 

 follicle: (a) mucopolysaccharides and/or alkaline phosphatase; (b) the 

 nucleic acids [D = DNA, R = RNA1 ; (c) thiol (SH) and disulphide 

 sulphur (S 2 ); (d) glycogen. In the shaft of the cortex the black areas are 

 the fully-stabilized hair, and the stippled are the pre-keratin = positive 

 thiol regions. 



Another unsolved problem is raised by the recent results of Fell, 

 Mellanby and Pelc (1954 and 1956) which revealed an apparent localization 

 of radioactive sulphur in nuclei of the cells of the oesophageal epithelium 

 after injection of labelled crystine. This would seem to imply that some 

 reaction involved in the addition of cystine to the cytoplasmic proteins has 

 its onset in the nuclei. Pelc (1958 and 1959) believes that cystine is ex- 

 changed against some DNA constituent which is itself broken down. Such 

 a view would link the final disappearance of the DNA with the late 

 synthetic processes (see also p. 264). However, the actual finding in these 

 experiments is the localization of sulphur in nuclei and this could equally 

 well be explained by an association between nuclear RNA and a sulphur- 

 containing protein, a view which would accord better with the other views 

 of the participation of RNA in synthesis. 



