542 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



orderly as it is represented in Fig. 172 a; possibly, therefore, some other 

 amino acid besides cystine — say glutamic acid — assists in bridging 

 this great distance. 



There is, however, another reason why the molecular frame is 

 unlikely to be a simple structure. Astbury (1933 c) advances plausible 

 arguments to show that, in the re-transformation of the /5-keratin of 

 stretched hairs into the folded a-keratin, side bridges must be broken 

 off. This, with a planar molecular frame, would be avoidable only if 

 all the parallel 2ig-2ag polypeptide chains could be folded simultane- 

 ously perpendicular to the projection plane of Fig. 172a without 

 breaking the cross links. If, however, the primary valence sheets are 

 linked in various directions, the individual polypeptide chains can no 

 longer be folded without breaking up the side-chain bonds. 



It is very significant that ordinary water is capable of disrupting 

 the bonds in question in the case of /3-keratin; for a hair stretched 

 to double its length and then dried has only to be placed in water 

 to regain its reversible elasticity. This means that drying brings about 

 only temporary, and not permanent, set. Nevertheless, if a hair 

 elongated 100%, is left for half an hour in a steam bath, it loses 

 the capacity to contract again to its original length, being now 

 permanently set and retaining this imposed length even when wetted 

 in what is known as "permanent set". This fact is put to use in the 

 hairdressing profession, for it is only when the hairdresser succeeds 

 in imparting permanent set to the /5-keratin produced at the curved 

 places in the hair that he can claim to have provided a "permanent 

 wave". The permanent setting of the /5-keratin is said to be achieved 

 by the prolonged action of the steam, whereby so many strong 

 bridges are laid between the keratin chains that hot water is subse- 

 quently unable to disrupt them. 



Elod, Nowotny and Zahn (1940) oppose Astbury 's theory that 

 keratin contains grid frames connected by sulphur bridges in the side 

 chains. Treatment of the wool with metallic mercury will convert 

 50% of the keratin sulphur to HgS. Removing half of the -S-S- 

 bridges should weaken the molecular frame, involving modification 

 of the properties of the wool. This, however, is not the case and these 

 investigators therefore assume that it is not the side chains which 

 build up the frame but, as in silk fibroin, hydrogen bonds (see Fig. 98, 

 p. 148) between the primary chains in the backbone planes (Nowotny 



