The thermal model and the transition from baryonic to mesonic freeze-out

The present status of the thermal model is reviewed and the recently discovered sharp peak in the K+/π+ ratio is discussed in this framework. It is shown that the rapid change is related to a transition from a baryon-dominated hadronic gas to a meson-dominated one. Further experimental tests to clarify the nature of the transition are discussed. In the thermal model the corresponding maxima in the Ξ/π and Ω/π ratios occur at slightly different beam energies. (orig.)