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==> In this proposal, more time is being requested for DROUAN.EDGEPAH
==> Time for this proposal is to be transferred from DROUAN.EDGEPAH
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In the proposal EDGEPAH we aimed at mapping, with ISOCAM, a few external spiral
edge-on  galaxies in dedicated PAH filters.  Given the first results (CAM LW and
PHT-S on one object:  NGC5907), this program appears successful since 2 IR bands
are  indeed  detected;  however,  because  of  the  short time available, only 4
filters  in  CAM-LW  were  selected:   this  is  clearly  not  enough for a safe
interpretation.   Also,  the  small  raster  was  not optimum for a proper flat-
fielding.   We  propose  here  to reshape the observations on one object not yet
observed (N891) using more CAM filters with optimized rasters, and a CVF mapping
on the central 6 kpc.  Allocated time from DROUAN.EDGEPAH is transferred here.
Beyond the proof of an universal presence of the PAH/VerySmallGrains component
in the  Diffuse Interstellar Medium of  spiral galaxies, observations of edge-on
galaxies,  combined  with  maps  at  radio wavelengths (HI, HII, CO) and near-IR
(stellar  population),  allow  to  study how the IR bands carriers abundance and
state  (ionization,  hydrogenation)  depend  on the conditions of excitation and
density  at  the  scale  of the galactic structure (nuclear region, bulge, disk,
giant  complexes);  this  is  even  more  important  since  ISO shown that large
variations  in line ratios (including new lines, such as the 11.0 mic band) were
related to the radiation density.  The CVF mapping gives a unique opportunity to
correlate spectral features with galactic structures at the scale of 200 pc.