  $\delta'$-function perturbations and Neumann boundary conditions are
incorporated into the path integral formalism. The starting point is the
consideration of the path integral representation for the one dimensional Dirac
particle together with a relativistic point interaction. The non-relativistic
limit yields either a usual $\delta$-function or a $\delta'$-function
perturbation; making their strengths infinitely repulsive one obtains
Dirichlet, respectively Neumann boundary conditions in the path integral.
