  Advection-dominated, high-temperature, quasi-spherical accretion flow onto a
compact object, recently considered by a number of authors, assume that the
dissipation of turbulent energy of the flow heats the ions and that the
dissipated energy is advected inward. It is suggested that the efficiency of
conversion of accretion energy to radiation can be very much smaller than
unity. However, it is likely that the flows have an equipartition magnetic
field with the result that dissipation of magnetic energy at a rate comparable
to that for the turbulence must occur by Ohmic heating. We argue that this
heating occurs as a result of plasma instabilities and that the relevant
instabilities are current driven in response to the strong electric fields
parallel to the magnetic field. We argue further that these instabilities heat
predominantly the electrons. We conclude that the efficiency of conversion of
accretion energy to radiation can be much smaller than unity only for the
unlikely condition that the Ohmic heating of the electrons is negligible.
