Certain segments of the internal ear, the vestibular apparatus, are concerned solely with the function of equilibrium, certain portions with hearing, and at least one section may have a dual role. As a continuous fluid mechanism, individual anatomic divisions and individual functions cannot always be isolated. The vestibular labyrinth has been shown to have a steady spontaneous discharge activity so that the two ears, operating equally and oppositely, maintain a balanced tonic activity. In this state of equilibrium, we are not aware of any sensation or labyrinthine function. Indeed, if both labyrinths are completely destroyed in man, this same state of equilibrium would generally continue except for special situations in which other mechanisms for maintenance of balance are either distorted or absent, such as in swimming under water, diving, or disease. This state of equilibrium is completely upset when the tonic balance is disturbed so that one labyrinth is more