  Experiment NA44 has measured proton and antiproton distributions at
mid-rapidity in sulphur and proton collisions with nuclear targets at 200 and
450 GeV/c per nucleon respectively. The inverse slopes of transverse mass
distributions increase with system size for both protons and antiprotons but
are slightly lower for antiprotons. this could happen if antiprotons are
annihilated in the nuclear medium. The antiproton yield increases with system
size and centrality and is largest at mid-rapdity. The proton yield also
increases with system size and centrality, but decreases from backward rapidity
to midrapidity. The stopping of protons at these energies lies between the full
stopping and nuclear transparency scenarios. The data are in reasonable
agreement with RQMD predictions except for the antiproton yields from
sulphur-nucleus collisions. PACS numbers 25.75.-q 13.85.-t 13.60.Rj
