We propose to observe atomic and ionic fine structure lines in
 nearby external galaxies.  Our observations will address two
 particular ascpects of the interstellar medium in these galaxies.

 First, an oversampled raster map of the grand design spiral galaxy
 M51 in the 158 micron CII, the 122 micron NII, and the 63 and 146
 micron OI fine structure lines will, by deconvolution, allow us to
 determine arm / interarm variations in the physical conditions and
 excitation mechanisms of the warm, mainly neutral interstellar
 medium and in the UV radiation field strength and spectral
 distribution.  This information will contribute to the understanding
 of the mechanisms that drive star formation in spiral patterns.

 Second, deep integration of the CII and NII fine structure line
 emission from the extended medium im M83 and Centaurus A will for the
 first time allow us to discern the cold, dense, neutral medium from
 the thinner, partly or fully ionized phases of the extended atomic
 medium as sources of CII line emission.  Temperatures and densities
 of the cold neutral medium in the outer disks of external galaxies
 will be derived for the first time.  In an analogous way, the
 physical conditions of the neutral atomic gas associated with the
 "shells" of Centaurus A will be explored.