[en] The author studies the physics of fermions in lattice regularized QCD, both abstractly and numerically. The author presents four papers, in the first showing how one can in principle extract the π⁺-π⁰ mass difference, in the second using a Monte Carlo simulation to compute the hadron spectrum and certain matrix elements on a small lattice, and in the third analyzing the symmetries of the staggered formulation of lattice fermions. Finally, the author presents preliminary results for the spectrum from a relatively large scale Monte Carlo simulation