A class of reversible Markov jump processes on a periodic lattice is d
escribed and a result about their scaling behavior stated: Under diffu
sion scaling, the empirical measure converges to a solution of the por
ous medium equation on the d-dimensional torus. The process can be vie
wed as a randomly interacting configuration of sticks that evolves thr
ough exchanges of stick pieces between nearest neighbors through a zer
o-range pressure mechanism, with conservation of total stick length.