Sleep is essential for physical and mental health. In the last 15 years there has grown up the concept of the brain stem reticular activating system. Electroencephalographic studies have shown two qualitatively different and alternating kinds of sleep, the orthodox (“slow wave”, or “forebrain“) and the paradoxical (”hind-brain“, “rapid eye movement”, “activated“, or “dreaming”) phases (Akert et al., 1965). It may be predicted that in the next decade attention will turn increasingly to the chemical basis of sleep. If a man is deprived of sleep for 100 hours, it is extremely difficult to keep him awake and one may suppose that an abnormal biochemical state exists within his central nervous system.