  The second order formalism for fermions provides a description of fermions
that is very similar to that of scalars. We demonstrate that this second order
formalism is equivalent to the standard Dirac formalism. We do so in terms of
the conventional fermionic Feynman rules. The second order formalism has
previously proven useful for the computation of fermion loops, here we describe
how the corresponding rules can be applied to the calculation of amplitudes
involving external fermions, including tree-level processes and processes with
more than one fermion line. We comment on the supersymmetric identities
relating fermions and scalars and the associated simplifications to
perturbative calculations that are then more transparent.
