Continuous Stimulation of the Labyrinth With Sustained Nystagmus

Abstract

In previous labyrinthine studies wherein caloric stimulation was employed, one of us (Spiegel) observed that reflex movements of the eyes still appeared even though the stimulus had lasted for several hours. As this fact seemed to shed some light on the mechanism of the caloric reaction of the labyrinth, a more detailed study of this phenomenon seemed worth while. METHODTo stimulate the labyrinth we constructed a simple apparatus by means of which water from a flowing faucet could continuously flow through tubes to the labyrinth and back again to the drain. At the end of the rubber tubing connecting with the animal, a small U-shaped brass tube was placed which consisted of two small brass tubes soldered side to side, each 7 cm. long and 2 mm. in external diameter. The ends that were to project into the auditory canal were closed by a brass cap. The common wall of both tubes was excised for a short distance near the cap, thus permitting water to flow freely from one tube into another. In one series of experiments, this U-shaped apparatus was introduced into the external ear, and in another group the ear drum was perforated, and the apparatus introduced so far into the middle ear that it touched the median wall. The water used for this stimulation, when leaving the apparatus, was usually at a temperature of 17 C. The maximum temperature used for stimulation with cold water was 23 C.; the minimum temperature was 8 C. To reach temperatures below 17 C., it was found necessary to conduct the water from the supply pipe through a coil of brass tubes immersed in an ice-salt mixture before its induction into the apparatus.In some experiments, the caloric responses were elicited with hot water (50 C.). In another group, stimulation was accomplished by galvanic current, which will be spoken of later in the article. The experiments were performed on cats kept under superficial ether anesthesia in as uniform and constant a degree as possible. Special care was taken to maintain the head rigidly in the desired position during the experiment. RESULTSThe latent period for the appearance of nystagmoid movements in the eyes, on stimulation with cold water, was in some cases very short, from about ten to twenty seconds, while in other cases it was observed