In the clinical literature, shock designates a group of grave symptoms which frequently lead to the death of the individual. At the postmortem examination no anatomic changes can be detected which would account for death and the grave symptoms preceding it. The fatal disturbance underlying the phenomenon of shock is, then, exclusively of a functional nature. From a purely scientific point of view, shock is, therefore, a subject pre-eminently belonging to the domain of pathologic physiology. It should be mentioned that the term shock employed in normal physiology is not identical with the syndrome in which we are interested here. The shock of the physiologists refers to the depression and suppression of spinal reflexes brought about by a direct injury to the cord. We shall not stop here to discuss the possibility of a common ground for both forms of shock. We wish, on the contrary, to point out one