We propose to do low resolution spectroscopy with ISOCAM and the
 SWS of two very distant IRAS galaxies in order to search for dust
features in their infrared spectrum, and to measure their continuum
 IR emission. The near and mid infrared domain is well suited since
 well known spectral features due to dust grains appear either in
 absorption: the silicate band at 9.8 microns and the ice band at
 13.3 microns, or in emission: the UIR bands at 3.3, 6.2, 7.7,
 8.6 and 11.3 microns. We shall also measure the overall
 continuum spectrum, a very important ingredient in the
 interpretation of faint galaxy counts and in the prediction of
 the extragalactic background in the infrared.
 Due to the high redshift of the targets, the wavelength of the dust
 features is shifted in the mid infrared where ISO is most sensitive.
 Such observations are of utmost importance for the understanding of
 the formation of galaxies. Moreover, the dust is an ubiquitous
 component of the interstellar medium which properties are still
 poorly known. These new observations in conditions very different
 from the galactic molecular clouds will help to understand the
 mechanism of formation and the nature of the dust.