..::::'"'Q7 0 col o Fig. 1 (top leit): Destruction o[ cortex by 5% Na_oS. Note separation o[ cuticle layers II{olinsky guard-hair section). x 350. Fig. 2 (top right): High cystinc content o,f cortex md almost complete absence from medulla (Sullivan reaction). x 700. Fig. 3 (middle le[t): tntense staining of medulla with Millon's reagent. x 700. Fig 4 (bottom felt)' Preferent :taining of medulla with Safranine TS. pH7. x 150. Fig 5 (bottom centre): Preferent ,taining of medulla with Safranine B. (Russian hare section). x 150. Fig. 6 (bottom right): •referential staining of cortex with Kiton Red G (Russian hare section). x 150. Fig. 7 second down on right): Human hair cross-sections. x 150. Fig. 8 (third do•n on right): 12educed wool fibres after 5 minutes in Feigl's reagent. x 43. 163

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS even in /•-kera.tin the polypeptide chains are not fully extended •4. Evidence in favour of this view is provided by the fact that the calcu- lated identity spacing for an ex- tended polypeptide chain is 7.2A, whereas the observed identity spac- ing is 6.7A. In 1947, electron microscope studies of the structure of fibrils and matrix derived from cortical cells of wool fibres digested with enzymes revealed that fibrils and matrix con- sist of corpuscles about 100A wide •. Much remains to be elucidated, and in particular the character of the linkage between corpuscles is of especial significance in view of the long range elasticity of wool fibres in water. More recently •6, examin- ation of X-ray diffraction patterns and infra-red spectra of synthetic polypeptides suggests that N-H bonds are essentially parallel to the fibre axis in a-keratin and perpen- dicular to it in /•-keratin, giving a fold similar to that suggested by Huggins•7: acid, glycogen and certain enzymes are also present in hair •. While these materials are of considerable interest to the biochemist they do not directly concern our present subject and will not be considered further. PHYSICO-CHEMICAL PROPERTIES. In view of what has already been said on the structure of keratin fibres, it will be clear that, since cortical cells constitute the major portion of human hair, physico- chemical properties find a ready explanation in terms of cross-link- age reactivity. Theoretically, the possible centres of fibre reactivity are salt linkages, cystine linkages, hydrogen bonds, imino- and acid amide groups, hydroxyl groups of serine and tyrosine, guanidine groups of histidin, and tryptophane side chains. Recent studies of par- tial hydrolysates of wool% particu- larly of acid peptides and cystine peptides,.suggest that in addition to, if not replacing, salt linkages, a dif- fuse scattering of positive charges The results of further work along these lines are awaited with consid- erable interest. Finally, it should be pointed out that various water-soluble, non- keratin con,ituents, such as uric with local concentrations of multiple negative charges on portions of the peptide chains may give rise to re- pulsive forcesl, especially between positively charged groups, which also help to decide the configuration 164