We propose to do a spectral exploration of the cold interstellar
 matter emission in the wavelength range accessible to ISO. The
 excellent sensitivity of ISO makes it unique to detect spectral
 features in low brightness extended sources. Spectra of the
 integrated galactic emission will be obtained on lines of sight
 with high column density of interstellar gas avoiding regions
 of massive star formation. The proposed observations will
 provide a spectral data base for several types of studies.
 The high column density, combined with long integration times,
 will provide a high signal to noise on the continuum and allow
 the detection of weak dust features, vibration modes of
 individual PAHs  molecules, molecular emission from hot spots
 in HI clouds associated with intermittent dissipation of
 turbulence, vibrational transitions of molecules seen in
 absorption against the diffuse emission of PAHs and very
 small grains, and the associated emission.
 This survey will provide a reference for the abundances and
 excitation mechanisms of important molecules like H2O, CO2,
 CH4, which are very difficult to observe in cold clouds.
 It will also test the role of infrared pumping by PAHs emission
 for molecules which are commonly used tracers of molecular clouds
 like CO and CS.
 This survey will be used in conjunction with the spectral survey
 of the central program on lines of sight of bright active star
 forming regions with the LWS Fabry-Perot. We propose to
 complement the spectral coverage for these lines of sight with
 a full SWS grating scan (at a cost of 10 % of the overall
 proposal).
 We intend to make the data base of this survey available to the
 community in reduced form as soon as possible.