  The freeze out of a massive nucleon gas through a finite layer with time-like
normal is studied. The impact of in-medium nucleon mass shift on the freeze out
process is investigated. A considerable modification of the thermodynamical
variables temperature, flow-velocity, energy density and particle density has
been found. Due to the nucleon mass shift the freeze out particle distribution
functions are changed noticeably in comparison with evaluations, which use
vacuum nucleon mass.
