In the waking and normal state, the whole brain is awake, all its parts acting in concert and preserving strict co-ordination. The reasoning faculties correct the senses; the senses correct the imagination; the intelligence controls the emotions; the emotions give vigour to the Will; the Will commands the entire mechanism of the body and expresses upon the external world the results of that combination of intelligent actions and emotions which we term “_the mind_.” In sleep this relationship is changed. The reasoning faculties cease to correct the senses; the senses no longer correct the imagination; the emotions are unable to influence the Will; the Will loses its command of body and mind alike. However it may be in dreamless sleep, in the condition of dream the entire mechanism certainly does not sleep. Some part of it is awake and active. What is that waking part? It is undoubted that the cerebral hemispheres are wholly or partially awake in the process of dream. In deep sleep the sense-ganglia are wholly asleep. In all sleep the senses sleep, only sometimes not so profoundly as completely to exclude cognizance, by the Conscious Self, of the sense-borne impressions. Sleep affects also the ganglia at the base of the brain that control the actions of the body. This, indeed, would appear to be the primary purpose of sleep. Sleep is obviously designed to give rest to the _material structure_—time for growth and renovation. It is for this reason that the Will, which in the waking state directs the motions of the structure, ceases to control it during sleep. The Will itself wakes—for we are self-conscious in dream—but in sleep the material mechanism does not obey the command of the Will, because itself is sleeping. The central and basal portions of the brain are, therefore, the seat of sleep. Unless they sleep we do not sleep. If they sleep we sleep, even although both brain hemispheres are at the same time wide awake. And this raises the question, so important in the Psychology of Dream; do the brain hemispheres, that duplex organ of the intelligence, sleep wholly or partially, or do they continue to be awake while the sense-brain and the body-moving brain are sleeping? This problem can be solved only by careful examination of the phenomena of dream. Suppose that Professor FERRIER could do with us as he did with the monkeys and dogs—take out a portion of the brain—and it were possible to remove altogether the middle and basal sections, leaving the hemispheres alone in the skull, would they sleep wholly or in part or, if awake, would they exhibit the phenomena of dream as they are now experienced? Contemplate, then, if you can, a duplex intelligent brain, in a state of activity, but cut off from all communication with the external world through the media of the senses and from all control over the body;—in fact, an isolated, self-acting, self-contained mechanism, the organ of intelligence and emotion. How would it work?