power to disturb sleep, i.e. the fulfillment 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