Distribution of marked perilymph to the subarachnoidal space.

In guinea pigs the tympanic perilymph of the basal turn was marked with fluorescing rhodamine. In the first series one drop of a 2% solution of the dye was applied onto the round window membrane. Since the perilymphatic space was not opened, the physiologic state of the communicating fluids perilymph and CSF was maintained. The dye appeared within 3-5 min via cochlear aqueduct in the subarachnoidal space. In the dead animal the speed of distribution was significantly less. This most probably indicates a weak physiologic flow of the perilymph through the aqueduct to the subarachnoidal space in living animals. In the second series, 2 ng of lyophilized rhodamine was instilled directly into the tympanic perilymph near the round window. Though hardly any additional volume was brought into the perilymph, the distribution of the dye was distinctly greater as a sign of the considerable sensitivity of the fluid system, even by the slightest manipulation.