That is a physiological or biological problem concerning which there is still much controversy. We can form no decision on the point, but I think we may attempt a psychological characterization of sleep. Sleep is a condition in which I wish to have nothing to do with the external world, and have withdrawn my interest from it. I put myself to sleep by withdrawing myself from the external world and by holding off its stimuli. I also go to sleep when I am fatigued by the external world. Thus, by going to sleep, I say to the external world, "Leave me in peace, for I wish to sleep." Conversely, the child says, "I won't go to bed yet, I am not tired, I want to have some more fun." The biological intention of sleep thus seems to be recuperation; its psychological character, the suspension of interest in the external world. Our relation to the world into which we came so unwillingly, seems to include the fact that we cannot endure it without interruption. For this reason we revert from time to time to the pre-natal existence, that is, to the intra-uterine existence. At least we create for ourselves conditions quite similar to those obtaining at that time--warmth, darkness and the absence of stimuli. Some of us even roll ourselves into tight packages and assume in sleep a posture very similar to the intra-uterine posture. It seems as if the world did not wholly possess us adults, it has only two-thirds of our life, we are still one-third unborn. Each awakening in the morning is then like a new birth. We also speak of the condition after sleep with the words, "I feel as though I had been born anew," by which we probably form a very erroneous idea of the general feeling of the newly born. It may be assumed that the latter, on the contrary, feel very uncomfortable. We also speak of birth as "seeing the light of day." If that be sleep, then the dream is not on its program at all, rather it seems an unwelcome addition. We think, too, that dreamless sleep is the best and only normal sleep. There should be no psychic activity in sleep; if the psyche stirs, then just to that extent have we failed to reduplicate the foetal condition; remainders of psychic activity could not be completely avoided. These remainders are the dream. Then it really does seem that the dream need have no meaning. It was different in the case of errors; they were activities of the waking state. But when I am asleep, have quite suspended psychic activity and have suppressed all but certain of its remainders, then it is by no means inevitable that these remainders have a meaning. In fact, I cannot make use of this meaning, in view of the fact that the rest of my psyche is asleep. This must, of course, be a question only of twitching, like spasmodic reactions, a question only of psychic phenomena such as follow directly upon somatic stimulation. The dream, therefore, appears to be the sleep-disturbing remnant of the psychic activity of waking life, and we may make the resolution promptly