  The Heat Kernel Method is applied to the constituent quark model. We
calculate the effect of thermal quark fluctuations on the meson action and the
resulting quark condensate and pi pi-scattering amplitude at finite
temperature. The quarks produce a chiral phase transition only by their effect
on the mesonic coupling constants. The s-wave isospin zero pi pi-scattering
amplitude diverges near the phase transition showing the necessity for a more
sophisticated treatment of meson fluctuations.
