First, it must be set in motion. Thus we are brought directly to the problem “What moves the mind?” Why does _this_ particular thought or feeling come into the mind at this moment rather than some other? The solution commonly accepted is that ideas come by _suggestion_. This means that ideas are, as it were, linked together and consequently that when one idea comes it is followed by certain other ideas which at some former time were connected with it. Probably the greater portion of the ideas that come to us apparently without such association are suggested by some impression brought by the senses, but received by the sensorium unconsciously to ourselves and that thus the “train of thought” is started. If it be so in one waking time, when the mind is busy with a multitude of impressions flowing in upon it from every sense—much more is it likely so to be when the impressions made by the senses are few, as is proved by the experience of every reader. In sleep, a slight sound falling upon the ear will suggest a dream of roaring cannon or rattling thunder. But the idea, once suggested, draws after it whole trains of associated ideas, and these ideas excite the _emotions_ precisely as they would have done had they been brought by the senses in the waking state. Thus far, then, we learn that the faculties which produce what we call ideas and sentiments and passions are not asleep. Some, if not all, of them are certainly awake and as active as in waking life. The Will, too, is not asleep, although powerless to command. In dream we _will_ to speak and do, but the body does not obey the Will. The efforts of the Will to command the limbs to move—as to escape from dreamed-of danger—and the failure of the limbs to obey, are often attended with consciousness of painful efforts made in vain. So far the phenomena of dream are consistent with the entire of the duplex brain organ of the intelligence being awake while the lower portion of the brain is sleeping. Certainly it is difficult to conceive of parts of such an organ as the two hemispheres sleeping, relaxed, and insensible, while other parts of it are awake and active. For, if Professor FERRIER is right, and distinct functions belong, not only to each ganglion but to various parts of each ganglion, the brain hemispheres, which are the material mechanism of the intelligence, must consist of many parts having different duties. We know that anatomically these parts, if they exist, are in intimate connection, lying closely packed together if not actually interlacing, and it is difficult to suppose that one part can be sleeping while its neighbour is awake, especially as sleep is attended, if not caused, by a depletion of blood from the fibres of the brain, retreating from the entire hemisphere and not from parts of it.