  Low temperature thermal conductivity, $\kappa$, of optimally-doped Bi2212 was
studied before and after the introduction of point defects by electron
irradiation. The amplitude of the linear component of $\kappa$ remains
unchanged, confirming the universal nature of heat transport by zero-energy
quasiparticles. The induced decrease in the absolute value of $\kappa$ at
finite temperatures allows us to resolve a nonuniversal term in $\kappa$ due to
conduction by finite-energy quasiparticles. The magnitude of this term provides
an estimate of the quasiparticle lifetime at subkelvin temperatures.
