  We revisit the notion that galaxy motions can efficiently heat intergalactic
gas in the central regions of clusters through dynamical friction. For
plausible values of the galaxy mass-to-light ratio, the heating rate is
comparable to the cooling rate due to X-ray emission. Heating occurs only for
supersonic galaxy motions, so the mechanism is self-regulating: it becomes
efficient only when the gas sound speed is smaller than the galaxy velocity
dispersion. We illustrate with the Perseus cluster, assuming a stellar
mass-to-light ratio for galaxies in the very central region with the
dark-matter contribution becoming comparable to this at some radius $r_s$. For
$r_s \la 400 {\rm kpc} \sim 3 r_{\rm cool}$--corresponding to an average
mass-to-light ratio of $\sim10$ inside that radius--the dynamical-friction
coupling is strong enough to provide the required rate of gas heating. The
measured sound speed is smaller than the galaxy velocity dispersion, as
required by this mechanism. With this smaller gas temperature and the observed
distribution of galaxies and gas, the energy reservoir in galactic motions is
sufficient to sustain the required heating rate for the lifetime of the
cluster. The galaxies also lose a smaller amount of energy through dynamical
friction to the dark matter implying that non--cooling-flow clusters should
have flat-cored dark-matter density distributions.
