Rothmund’s and Redfern Davis’ instruments are modifications of Wurtz’s original design. “The Rothmund instrument is a modification of Wurtz’s, but possesses the advantage of sliding pieces and interchangeable plugs, by means of which it can be adapted to all cases making it decidedly preferable.  The objection of papers is obviated by having it made of hard rubber, such as is now constructed by Tiemann & Co. lf New York.”  The plug or “invaginator” of Davis’ instrument is hinged at the proximal end and can thus be expanded to fill a more capacious canal if necessary.