 the vital spirits regulate all vegetative functions of plants and animals. Organs responsible for these functions, for digestion, assimilation, etc., seem to act by perception, mere reaction to local stimuli, but these reactions are coordinated by the vital spirit. These functions flow from the spirit's airy-flamy constitution. The spirit has the softness of air to receive impressions and the vigour of fire to propagate its actions. (Rees in OFB VI, 202–3) 