This is a difficult, rigorous but absolutely fascinating scientific study of how and why we sleep. Hartmann, Professor of psychiatry at Tufts and director of the Sleep and Dream Laboratory at Boston State Hospital, reviews and summarizes current research based on evidence derived from chemistry, pharmacology, neurophysiology and psychoanalysis. Unlike most investigators in the field Dr. Hartmann is no mechanist; he is primarily interested in the systemic functions of sleep -- just how it acts to restore physical and mental equilibrium in the human organism. Building toward the development of an integrative, holistic theory Hartmann looks at the effects of sleep deprivation; at personality differences between long and short sleepers; at the sleep cycle itself and how it is affected by anxiety, physical exertion, stress, drags and mental illness; at the impairment of normal adaptive functions (memory, concentration, learning ability) caused by lack of sleep; at the behavioral symptoms of fatigue in children and adults, including irritability, anger, loss of will power, depression (i.e. ""clear evidence of ego regression""). Hartmann tells us that scientists have positively differentiated between ""synchronized"" or S-sleep during which we remain quiescent and dreamless and the far more dynamic ""desynchronized"" or D-sleep which neurologically resembles the waking state. Eventually Hartmann focuses on D-sleep, linking it to the synthesizing of certain chemical substances in the brain -- the catecholamines -- which appear to govern normal functioning of the superego and the higher faculties: focused attention, optimism and self-confidence and overall ""self-guidance."" In a speculative postscript he predicts that mental states, so far ""explained"" in psychoanalytic terms, ""will turn out to be restatable in terms relating to the function of brain catecholamine systems""; in other words, sleep may hold the key to translating the workings of the subjective ""mind"" or ""psyche"" into an empirical brain chemistry. Lucid and important enough to preclude even a scientific ignoramus dozing off.