  The notion of the integral over the anticommuting Grassmann variables is
applied to analyze the fermionic structure of the 2D Ising model with quenched
site dilution. In the $N$-replica scheme, the model is explicitly reformulated
as a theory of interacting fermions on a lattice. For weak dilution, the
continuum-limit approximation implies the log-log singularity in the specific
heat near $T_c$.
