For example, raw mangoes shrivel when pickled in brine (salt water);
wilted flowers revive when placed in fresh water, blood cells collapse
when suspended in saline water, etc If we look into these processes we
find one thing common in all,
that is, all these substances
are bound by membranes These membranes can be of
animal or vegetable origin
and these occur naturally
such as pig’s bladder or
parchment or can be
synthetic such as cellophane These membranes appear to
be continuous sheets or
films, yet they contain a
network of submicroscopic
holes or pores