# Eliminating longitudinal photons

In Feynman's paper "Mathematical Formulation of the Quantum Theory of Electromagnetic Interaction" he writes that the semiclassical Coulomb interaction can be written by eliminating longitudinal photons. I believe this was done by Fermi and Bethe in 1932, however there paper was written in German so is hard to read. Does anyone have an explanation or reference for how to eliminate longitudinal photons (in the Coulomb gauge I presume) in QED?