The phenomena of dreams may well seem at first sight to form a world of their own, having no discoverable links of connection with the other facts of human experience. First of all, there is the mystery of sleep, which quietly shuts all the avenues of sense and so isolates the mind from contact with the world outside. To gaze at the motionless face of a sleeper temporarily rapt from the life of sight, sound, and movement--which, being common to all, binds us together in mutual recognition and social action--has always something awe-inspiring. This external inaction, this torpor of sense and muscle, how unlike to the familiar waking life, with its quick responsiveness and its overflowing energy! And then, if we look at dreams from the inside, we seem to find but the reverse face of the mystery. How inexpressibly strange does the late night-dream seem to a person on waking! He feels he has been seeing and hearing things no less real than those of waking life; but things which belong to an unfamiliar world, an order of sights and a sequence of events quite unlike those of waking experience; and he asks himself in his perplexity where that once-visited region really lies, or by what magic power it was suddenly and for a moment created for his vision. In truth, the very name of dream suggests something remote and mysterious, and when we want to characterize some impression or scene which by its passing strangeness filled us with wonder, we naturally call it dream-like. _Theories of Dreams._ The earliest theories respecting dreams illustrate very clearly this perception of the remoteness of dream-life from waking experience. By the simple mind of primitive man this dream-world is regarded as similar in its nature or structure to our common world, only lying remote from this. The savage conceives that when he falls asleep, his second self leaves his familiar body and journeys forth to unfamiliar regions, where it meets the departed second selves of his dead ancestors, and so on. From this point of view, the experience of the night, though equal in reality to that of the day, is passed in a wholly disconnected region.[69]