THE HISTOCHEMICAL DEMONSTRATION OF CYSTINE-CONTAINING STRUCTURES BY METHODS INVOLVING ALKALINE HYDROLYSIS

1) Hydrolysis of combined cystine at pH 12.8 gives rise to reaction products capable of converting soluble, relatively colourless, tetrazolium salts into insoluble formazan dyes. 2) Both normal and abnormal keratins are demonstrated by the reaction. 3) Cystine-free structures which also reduce tetrazolium salts at pH 12.8 are present in tissue sections. These are either lipid-containing or reducing sugar-containing, but distinction between these two groups and the cystine-containing group of structures is histochemically possible. 4) The alkaline tetrazolium reaction is considered to form the basis of a useful method both for research into the process of keratinisation and also for the routine diagnosis of abnormal tumour keratins.