the power to disturb sleep, i.e. the fulfilment of the foreconscious wish. This is probably due to certain relations of energy into which we have no insight. If we possessed such insight we should probably find that the freedom given to the dream and the expenditure of a certain amount of detached attention represent for the dream an economy in energy, keeping in view the fact that the unconscious must be held in check at night just as during the day. We know from experience that the dream, even if it interrupts sleep, repeatedly during the same night, still remains compatible with sleep. We wake up for an instant, and immediately resume our sleep. It is like driving off a fly during sleep, we awake ad hoc, and when we resume our sleep we have removed the disturbance. As demonstrated by familiar examples from the sleep of wet nurses, &c., the fulfilment of the wish to sleep is quite compatible with the retention of a certain amount of attention in a given direction.
But we must here take cognisance of an objection that is based on a better knowledge of the unconscious processes. Although we have ourselves described the unconscious wishes as always active, we have, nevertheless, asserted that they are not sufficiently strong during the day to make themselves perceptible. But when we sleep, and the unconscious wish has shown its power to form a dream, and with it to awaken the foreconscious, why, then, does this power become exhausted after the dream has been taken cognisance of? Would it not seem more probable that the dream should continually renew itself, like the troublesome fly which, when driven away, takes pleasure in returning again and again? What justifies our assertion that the dream removes the disturbance of sleep?
That the unconscious wishes always remain active is quite true. They represent paths which are passable whenever a sum of excitement makes use of them. Moreover, a remarkable peculiarity of the unconscious processes is the fact that they remain indestructible. Nothing can be brought to an end in the unconscious; nothing can cease or be forgotten. This impression is most strongly gained in the study of the neuroses, especially of hysteria. The unconscious stream of thought which leads to the discharge through an attack becomes passable again as soon as there is an accumulation of a sufficient
