Comment on ``Correct definition of the Poynting vector in electrically
    and magnetically polarizable medium reveals that negative 
    refraction is impossible.''

    A. Favaro, P. Kinsler, M.W. McCall 

    Blackett Laboratory, 
    Imperial College London,
    Prince Consort Road,
    London SW7 2AZ,
    United Kingdom.

    Opt. Express 17, 15167-15169 (2009).
    http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-17-15167
    doi: 10.1364/OE.17.015167

Physically valid electromagnetic continuity equations can be generated
from either the usual form of the Poynting vector $\vec{E} \times
\vec{H}$ or the alternative $\vec{E} \times \vec{B}$ form.  However,
the continuity equations are not identical, which means that
quantities following from $\vec{E} \times \vec{H}$ cannot always be
compared directly to those from $\vec{E} \times \vec{B}$.  In
particular, the work done on the bound current densities are
attributed differently in the two representations.  We also comment on
the negative refraction condition used.