Numerous other examples of a similar character might be related to illustrate the fact that the brain is a reservoir of sensory impressions, some of which, at the moment of their original incidence, have aroused the mind to a greater or less degree of conscious attention, and have then all lapsed into a latent or potential condition. But, though latent, they are none the less persistent, and only await the suppression of other inhibitory forces to become once more capable of arousing attention. Such inhibitory impulses are continually furnished by the action of the sensory organs on the one hand, and by the energy of the mind upon the other. So soon, therefore, as the organs of sense and of voluntary impulse are sealed with sleep, if the remaining portions of the brain are still operative, and are left to their own unrestrained activity, a more or less disorderly series of ideas occupies the mind. This constitutes a dream. The difference, therefore, between waking thought and a dream is analogous to the difference between a page upon which the words have been arranged in a rational order, and another page upon which some of the same words have been set down at random. Inasmuch as the majority of our sensations are derived through the organs of sight, and since the larger portion of the sensory region of the cortex of the brain is concerned in the act of vision, it is no more than might be expected that the ideas suggested in sleep should generally proceed from the visual apparatus of the brain. The superior power of visual impressions to attract attention may also serve to explain the fact that the majority of dreams are composed of images that were originally perceived in the act of vision. Hence our dreams, for the most part, constitute a series of pictures undisturbed by sound, or by other forms of sensation. But this is not always so. It is highly probable that when the organs of external sense are allowed to sleep without disturbance, our dreams consist of visual impressions alone. But, if any unusual sound, or smell, or other sensation is experienced during sleep, it may penetrate the field of consciousness, and may become the starting point of a dream quite filled with sounds. Thus a young lady, who had passed the evening at a musical concert, was aroused, soon after retiring, by the striking of a clock which had been recently placed in her chamber. At the moment of waking, she was dreaming of an orchestral performance of Wagner’s music. Doubtless the dream was suggested by the unaccustomed sound of the clock.