A broad survey of the literature since 1929, reviewing the effects of barbiturates upon the brain, and subdivisions of it, respiration, circulation, the spinal cord, secretory nerves, smooth muscle, blood, and O2 consumption. The author also discusses classification of these drugs on the basis of duration of action, the relation of their chemical structure to their physiological effect, antagonists and synergists for them among other drug groups, the mode of their elimination and detoxication; and phases of clinical interest, such as poisoning, chronic intoxication, pathological changes in tissues, habituation, and indications for their use.