Sentence:  In a long commentary which he has inserted in the published text of the first act of the play , he says at one point : `` However , that experience never raised a doubt in his <WSD>mind</WSD> as to the reality of the underworld or the existence of Lucifer 's many faced lieutenants . 
Meaning of the word marked with <WSD> tags:  that which is responsible for one's thoughts and feelings; the seat of the faculty of reason