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Short communications in the form of Letters to the Editor are intended to provide prompt publication of significant new research results and to permit an exchange of views on papers previously published in the JOURNAL. These communications are not submitted to formal review as are research papers, and the editors do not assume any share of the author's responsibility for the information given or the opinions expressed. When work previously published in the JOURNAL is the subject of critical comment, the authors of the original paper are given an opportunity to submit a reply, which will be published concurrently when possible.To the Editor TEXTILE RESEARCH JOURNAL D ear Sir: Supercontraction is a phenomenon which has been widely studied in connection with the structure of keratin fibers. It is a spontaneous, and generally permanent, decrease in fiber length which occurs upon treatment with reagents which are able to split various types of bonds such that gross molecular rearrangement occurs [ 5 ] . Supercontraction has been noted primarily in the case of reactions which rupture disulfide linkages, such as by reaction with boiling bisulfite solutions [4,6].More recently work has been published in which supercontraction was demonstrated with solutions considered primarily as reagents which break hydrogen bonds [1,2,5,7,8,9]. While these nonreductive reagents would not be expected to split the disulfide bonds in keratin, nonetheless the conditions under which contraction was observed-prolonged treatment in aqueous systems at elevated temperatures and the use of highly concentrated solutions which produce excessive swelling-make it possible that some splitting of disulfide linkages might also be occurring. In fact, Alexander [1] has reported a small decrease in the cystine content of wool as a result of supercontraction in hot lithium bromide solutions. On the other hand, it has been shown that alkali-treated keratin fibers in which substantial amounts of cystine S have been lost still supercontract in LiBr [1] and phenol [9] ] at 100 ° C, suggesting that cystine breakdown is not involved.As part of a broad study of the reaction of wool and hair with lithium bromide solutions * it was considered desirable to isolate, if possible, the contraction effect produced by secondary-bond rupture from that produced by rupture of the disulfide bond, if, indeed, any of the latter occurs. This possibility occurred to us through a technique previously described in a note from these laboratories [4] in which it was shown that simple replacement of the disulfide linkages in keratin fibers by stable bisthioether linkages results in modified fibers which do not supercontract in boiling bisulfite solutions. This behavior clearly demonstrates the need for disulfide rupture in such a reaction. A modified keratin fiber in which the labile disulfide bonds have been replaced by thioether linkages so that they can no longer participate in supercontraction reactions should be a desirable model substance for evaluating the supercontraction eff...