Here the fibril has been removed entirely by the
etchant and it was appear a group of parallel cylindrical hollows.
At high magnification, the diameter of the dark are reduced as
the observed depth increases. This would arise from the etching
mechanism. This process should not give any different features of
the hole for indicating the location of sorbitol derivatives fibrils
which are perfectly or nearly perfectly aligned. Table 5 shows
diameter of dark spots calculated from Fig 3 compare with
diameter of fibril derived from SEM micrographs. It can be seen
that the diameters derived from both techniques are similar.