ethereal substance

... there they him laid
Gnashing for anguish and despite and shame
To find himself not matchless, and his pride
Humbl'd by such rebuke, so farr beneath
His confidence to equal God in power.
Yet soon he heal'd; for Spirits that live throughout
Vital in every part, not as frail man
In Entrailes, Heart or Head, Liver or Reines;
Cannot but by annihilating die;

_Paradise Lost_, VI.339-347