In Sleep the brain is unable to convey its commands to the body. The nerves do not obey. Something that operates between the brain and the nerves and which was active in the waking state is inactive in sleep. What is that _something_? It is the _Will_. The Will has ceased to act and thus the body has ceased to be controlled by the mind. This is the process by which the needful rest of the body is brought about. Here the question comes, in what part of the mechanism does the change occur that thus causes the suspension of the power of the Will and the partial severance of the Conscious Self from its normal control of the body? _How_ does sleep accomplish so great a revolution? If the whole mental mechanism were inactive in sleep this question would be answered easily. We should say, “the entire of the brain is sleeping and therefore the whole mechanism is at rest. The motive forces that move and direct the machine in its waking state have ceased for a time from their work and the structure stands still.” But that is not the condition. All the forces have not ceased from their work. The vital force continues in full activity, keeping the machinery in motion and performing the work of nutrition, reparation and growth. The _mind_ is not at rest; the phenomena of dream directly contradict such a conclusion. The whole mental mechanism is certainly not at rest. A part of it is very busy. The hemispheres of the brain are not sleeping—or sleeping but partially. They are enacting dreams. They are in truth working with infinitely greater speed and power when we are asleep than when we are awake! If, then, the brain hemispheres are waking above and the body is sleeping below, the communication between them must be severed by sleep at some part of the mechanism below the brain hemispheres (which are the mechanism of the Intelligence) and the point where the brain branches into the nerve system—which is the mechanism by whose action the vital force forms and sustains the organic structure.