Resistant Components of the Cortex of Animal Hair

THE possibility that there exists beneath the scaly layer or cuticle of animal hair another peripheral layer has been discussed both in these columns 1,2 and elsewhere 3,4 . The supposed layer has been named variously subcutis, between-membrane, and cortical mantle. The most convenient way to show that there does exist a resistant non-keratinous residue beneath the cuticle was described by Alexander and Earland 4 . Hair or wool is oxidized with weak aqueous peracetic acid and then extracted with dilute ammonia solution. The oxidation destroys the disulphide cross-links which stabilize the keratin, rendering it soluble in alkali. The non-keratinous residue consists of ( a ) thin tubes each looking like a cast of the cuticle and consisting mainly of the thin membrane, the epicuticle, which envelops the scales externally, and ( b ) a cortical residue, which seen from the side looks like a rather tenuous tube of cortical cells 2 . This latter was thought to be the new morphological component, the subcutis 4 .