As the museum turns 20, officials understand that the demise of
those who survived the prison camps as children means looking
backward in a different way.    It won't be long before no
eyewitnesses remain.    You can read all the documentation of
the Holocaust in the world, said Diane Saltzman, director of
survivor affairs at the U.S. Holocaust Memorial Museum, "but
hearing somebody's voice, sitting across the table or across the
room from a human being, there's no true substitute."   "I tell
my students annually that they have a special responsibility,"
he said. "They are the last generation that will be able to say
that they personally knew survivors of the Holocaust. It is a
big change, just like it was when the last Civil War veteran
passed from the scene."  The Holocaust, now "perceived history,"
will become "received" history, Sarna said. The challenge is
that it doesn't recede from memory.  Holocaust educators take
heart in the many institutions and younger people committed to
ensuring that future gene