  A new method for the determination of the spin-1/2-3/2-mixing angle and the
range parameter of the quarkmodel wavefunction of the resonance
$S^-_{11}(1535)$ is presented. The method ist based on a quantitative
calculation of the total cross section of $pp\to pp\eta$ at threshold. The
quantitative on-shell treatment of ISI and FSI is discussed.
