CHEMICAL BEHAVIOR OF PLANETARY-NEBULAE AND GALACTIC ABUNDANCE GRADIENTS

All modem determinations of chemical abundances of He/H, O/H, C/H, N/H and Ne/H in 277 galactic Planetary Nebulae have been used to update o ur knowledge of the chemical behaviour of Planetary Nebulae, as a whol e and in Peimbert's groups. The data have been used to set up the prob lem of the chemical gradients in the Galaxy from Planetary Nebulae. Th e Interstellar Medium has been found to be more inhomogeneous in the p ast epochs of the Galaxy than in the present time.