  We report far infrared transmission measurements on single crystal samples
derived from Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$. The impurity scattering rate of
the samples was varied by electron-beam irradiation, 50MeV $^{16}$O$^{+6}$ ion
irradiation, heat treatment in vacuum, and Y doping. Although substantial
changes in the infrared spectra were produced, in no case was a feature
observed that could be associated with the superconducting energy gap. These
results all but rule out ``clean limit'' explanations for the absence of the
spectroscopic gap in this material, and provide evidence that the
superconductivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ is gapless.
