  We point out that a recent experiment by Keijsers, Shklyarevskii and van
Kempen [Phys. Rev. Lett. 77, 3411 (1996)] on metallic glass point contacts
containing two-level systems (TLS) effectively measures for the first time the
conductance contributions of individual TLSs (previous experiments averaged
over a distribution of TLSs). For this case the predictions of the Kozub-Kulik
theory for the TLS-electron interaction differ from those of the
Vladar-Zawadowski theory, the latter giving much better agreement with
experiment.
