LII Experimental Observations on the Fluid Physiology of the Inner Ear

Abstract

Avian erythrocytes injected into the sub-arachnoid space of the posterior cranial fossa were caught in great numbers in the fine fibrous meshwork of the cochlear aqueduct, and in many ears passed through the aqueducts to enter the perilymphatic spaces. In ears with blocked aqueducts there were no accumulations of cells in the cranial ends of the aqueducts and no cells were found in the perilymph. Experimental obstruction of the aqueduct for periods up to ten months failed to produce inner ear changes. Apparently the aqueduct is not necessary for the maintenance of perilymph volume. Destruction of the endolymphatic sac failed to produce changes in endolymph volume for observation periods of many months. Blocking the endolymphatic duct at its vestibular end failed to result in disten-tion of the sac which should occur if it is a secreting structure. The application of irritating aluminum salts to the wall of the sac failed to result in increased endolymph volume. The experiments suggest that the endolymphatic sac is not essential for the maintenance of endolymph volume but may serve some enzymatic or metabolic function for the inner ear. An experiment in which fluids were perfused through cochleas for the demonstration of acetylcholinesterase showed a system of fluid channels connecting the scala tympani with the organ of Corti. The pathways begin in a series of small openings in the inferior shelf of the osseous spiral lamina and pass among the bundles of nerve fibers to reach the habenula perforata and the organ of Corti. This system of channels probably brings perilymph to the organ of Corti, providing a suitable fluid environment for nerve transmission. Mechanical injuries were made to the cochleas of several animals resulting in rupture and permanent fistulization of the cochlear ducts. The hearing tests of these animals did not register functional losses describable to the fistuals. Two animals had near normal hearing for low frequencies with tears in Reissner''s membrane in the basal turn. Thus, it appears that fistulas of the cochlear duct have little or no effect on cochlear function in regions separated from the fistulae by several millimeters. Because of the injury to the sense organ, the experiments provide no information on the effect of the fistulae on the adjacent organ of Corti.