  A remarkable theoretical prediction for a crystalline (polymerized) surface
is that its Poisson ratio (\sigma) is negative. Using a large scale Monte Carlo
simulation of a simple model of such surfaces we show that this is indeed true.
The precise numerical value we find is (\sigma \simeq -0.32) on a (128^2)
lattice at bending rigidity (kappa = 1.1). This is in excellent agreement with
the prediction (\sigma = -1/3) following from the self-consistent screening
approximation of Le Doussal and Radzihovsky.
