  In a continuum description of materials, the stress tensor field $\bar{%
\bar{\sigma}}$ quantifies the internal forces the neighbouring regions exert on
a region of the material. The classical theory of elastic solids assumes that
$\bar{\bar{\sigma}}$ determines the strain, while hydrodynamics assumes that
$\bar{\bar{\sigma}}$ determines the strain rate. To extend both successful
theories to more general materials, which display both elastic and fluid
properties, we recently introduced a descriptor generalizing the classical
strain to include plastic deformations: the ``statistical strain'', based on
averages on microscopic details (``A texture tensor to quantify deformations''
M.Au., Y.J., J.A.G., F.G, companion paper, {\em Granular Matter}, same issue).
Here, we apply such a statistical analysis to a two-dimensional foam steadily
flowing through a constriction, a problem beyond reach of both theories, and
prove that the foam has the elastic properties of a (linear and isotropic)
continuous medium.
