Still another cause for the production of dreams is to be found in the more or less complete suspension of the power of volition which accompanies sleep. Every act of attention is the result of exercise of the will. But the perfect exercise of the will is dependent upon the perfect development and wakefulness of the brain. So soon as sleep begins to invade the brain, the will begins to lose its normal incitement to action, and finally it becomes almost wholly disconnected from the muscular organs. In this state the sleeper may desire to perform some act--he may wish to move his limbs or to cry out aloud, but he can move neither hand nor foot, he cannot utter a sound. In other instances a partial connection between the will and the locomotive organs persists, and various orderly movements can still be produced. In like manner the control of the will over the succession and association of ideas may be either wholly, or only partially, lost in sleep. The deeper the sleep the more complete the loss of such control; hence the greater incoherence as well as feebleness of impression which is characteristic of dreams when sleep is profound. The vivid and panoramic succession of visual conceptions which constitutes a “vision,” occurs during light and partial sleep, when the will is still capable of in some measure guiding the procession of ideas. For a similar reason the higher faculty of judgment, and especially the power of arriving at moral conclusions, is in great measure suspended during sleep. Like the power of volition, the activity of the moral sense is dependent upon a certain functional perfection in the brain. When the capacity of the brain is depressed by drugs or by disease, or by sleep, the moral sensibilities are the first to disappear. Hence the non-moral character of the impressions usually experienced during the act of dreaming. We feel neither surprise nor regret at the incidents of ordinary dreams. It is only when the border line of wakefulness is reached that the dreamer feels ashamed of walking naked in his dream, or feels compunction for an act of crime, or experiences emotions of joy or sorrow in connection with the incidents of his vision. A dream may, therefore, be defined as the occupation of the field of consciousness during sleep by a succession of ideas more or less completely withdrawn from the guidance of the senses and from the control of the will. A great variety of dreams may thus be admitted, ranging all the way from those products of mere absence of mind which constitute _revery_, down to the faintest and feeblest stirrings of consciousness which have been always observed during the act of waking from the profoundest sleep.