Abstract
Dirac's formalism for constrained Hamiltonian systems is applied to the statistics of incompressible fluid membranes. The effect of tangential flows is completely taken into account. They are shown to induce long-range correlations between extrinsic curvatures at the classical level, but with a sign opposite to the one previously obtained by Förster. However, these forces are shown to be screened by thermal undulations. This validates the calculation of the renormalization of the bending rigidity by Peliti and Leibler, which assumes no large distance correlations.