gradually helped to dissolve a good part of the mystery which once hung like an opaque mist about the subject.  In this way, our dream-operations have been found to have a much closer connection with our waking experiences than could be supposed on a superficial view.  The materials of our dreams are seen, when closely examined, to be drawn from our waking experience.  Our waking consciousness acts in numberless ways on our dreams, and these again in unsuspected ways influence our waking mental life.[71] Not only so, it is found that the quaint chaotic play of images in dreams illustrates mental processes and laws which are distinctly observable in waking thought.  Thus, for example, the apparent objective reality of these visions has been accounted for, without the need of resorting to any supernatural agency, in the light of a vast assemblage of facts gathered from the by-ways, so to speak, of waking mental life.  I need hardly add that I refer to the illusions of sense dealt with in the foregoing chapters.

Dreams are to a large extent the semblance of external perceptions.  Other psychical phenomena, as self-reflection, emotional activity, and so on, appear in dream-life, but they do so in close connection with these quasi-perceptions.  The name “vision,” given by old writers to dreams, sufficiently points out this close affinity of the mental phenomena to sense-perception; and so far as science is concerned, they must be regarded as a peculiar variety of sense-illusion.  Hence the appropriateness of studying them in close connection with the illusions of perception of the waking state.  Though marked off by the presence of very exceptional physiological conditions, they are largely intelligible by help of these physiological and psychological principles which we have just been considering.

The State of Sleep.

The physiological explanation of dreams must, it is plain, set out with an account of the condition of the organism known as sleep.  While there is here much that is uncertain, there are some things which are fairly well known.  Recent physiological observation has gone to prove that during sleep all the activities of the organism are appreciably lowered.  Thus, for example, according to Testa, the pulse falls by about one-fifth.  This lowering of the organic functions appears, under ordinary circumstances, to increase towards midnight, after which there is a gradual rising.

The nervous system shares in this general depression of the vital activities.  The circulation being slower, the process of reparation and nutrition of the nerves is retarded, and so their degree of excitability diminished.  This is clearly seen in the condition of the peripheral regions of the nervous system, including the sense-organs, which appear to be but very slightly acted on by their customary stimuli.