But we must go still further back. To conceive properly the nature of trance, it is necessary to form clear ideas of the state of the mind in ordinary sleeping and waking. During our ordinary waking state, we are conscious of an uninterrupted flow of thought, which we may observe to be modified by three influences--the first, suggestions of our experience and reflections, impulses of our natural and acquired character; the second, present impressions on our senses; the third, voluntary exertion of the attention to detain one class of ideas in preference to others. Further, we habitually perceive things around us, by or through sensation. But on some, and for the most part trivial occasions, we seem endowed with another sort of perception, which is either direct, or dependent on new modes of sensation. Again, the balance of the mental machinery may be overthrown. The suggestions of the imagination may become sensorial illusions; the judgment may be the subject of parallel hallucinations; the feelings may be perverted; our ideas may lose connexion and coherence; and intelligence may sink into fatuity. So much for our waking state. During sleep, there are no adequate reasons for doubting that the flow of our ideas continues as uninterrupted as in a waking state. It is true, that some persons assert that they never dream; and others that they dream occasionally only. But there is a third class, to which I myself belong, who continually dream, and who always, on waking, distinctly discern the fugitive rearguard of their last sleep thoughts. The simplest view of these diversified instances, is to suppose that all persons in sleep are always dreaming, and that the spaces seemingly vacant of dreams, are only gaps in the memory; that all persons asleep always dream, but that all persons do not always remember their dreams. The suggestive influences that modify the current of ideas in sleep, are not so numerous as those in operation in our waking state. The principal, indeed in general the exclusive, impulse to our dreaming thoughts, is our past experience and existing character, from and in obedience to which, imagination moulds our dreams. Not that sensation is suspended in sleep. On the contrary, it appears to have its usual acuteness; and impressions made upon our senses--the feelings produced by an uneasy posture, for instance, or the introduction of sudden light into the room, or a loud and unusual noise, or even whisperings in the ear--will give a new and corresponding direction to the dreaming thoughts. Sensation is only commonly not called into play in sleep: we shut our eyes; we even close the pupils; we cover up our ears; court darkness and quiet; knowing that the more we exclude sensible impressions the better we shall sleep.