It's not surprising at all that Saint-Saens would want to use the
xylophone in his "Danse Macabre" to imitate the sounds of bones
rattling.  The xylophone had been seen before in early artwork
dealing with Death.  At
http://www.vsl.co.at/english/instruments/drums/mallets/xylophone/History.htm

  "in his famous painting Dance of Death from 1523 Hans Holbein the
  Younger imbues the xylophone with death imagery; a skeleton in the
  procession plays a portable xylophone, the sound of which thus comes
  to symbolize the rattling of bones.  This is the first known
  portrayal of a xylophone in Europe."

Saint-Saens also used the xylophone in his "Carnival of the Animals".
In that work, he used the xylophone to imitate the sound of old fossil
bones.

Danielle Squyres

 [ Danielle is a professional percussionist with a special fondness
 [ for "hammered" melodic instruments like the xylophone.  ;-)
 [ -- Robbie