A N e w Theory of the Pathophysiologr]BRYNJULF INGEBRIGTSEN T Numerous hypotheses have been advanced to explain the mechanism of cerebral concussion. Recently, Jacobsen (1963) presented a list of 26 hypotheses brought forward since 1878. These theories are all based on the concept of direct or indirect damage to the cerebral tissue. Various types of direct damage have been proposed, such as compression of cerebral cortex or brain stem, mass movement of brain, and more unspecified direct effect on certain cerebral centers. Indirect brain damage might be caused by impairment of the circulation of blood or cercbrospinal fluid. For full discussion of these hypotheses the reader