A contribution to the experimental study of a caloric nystagmus

Abstract

Barany, as early as 1905, advanced the theory that the nystagmus whichappears by cooling and by healing in the external auditory meatus, is due to amovement of the cupula arising from a current of the endolymph in the'semicircular canals, especially in the lateral canal. The nystagmus is producedby the increased or diminished gravity of the fluid in its most exposedparts doe to the change of temperature. The temperature on reaching the labyrinthis conducted from the wall of the external auditory meatus to the semicircularcanals through the substance of the temporal bone.Later on, Barany's theory was experimentally provel by several investigators, such as, Magnus and de Kleijn, de Kleijn and van Leeuwen, Maier and Lion etc. Kobrak, however, bing dubious to the correctness of Barany's theory, as a resultof his “minimal irritation” experiment (5cc water with a difference of temperatureof 5°-10°C from the temperature of the body), has reported that it is quetionableif the temperature of the wall of the external auditory meatus can be physicallyconducted to the labyrinth by such minimal irritation. The study of the thermalrelation between the external auditory meatus and the labyrinth on caloric nystagmushas lately made great progress. Schmaltz and Volger have proved the conductionof temperature from the external auditory meatus to the semicircular canal andthe appearance of the so-called caloric nystagmus by their experiment on a skulland in the course of ear operations on patients, making use of thethermo-electric current. Dohlman has measured the capacity of air and of a compactbone to conduct temperature in the experimental investigation of the path ofconduction in caloric nystagmus. The result that the conducting capacity of compactbone was 6 times faster than that of air, has led him to the conclusion that in theconduction of temperature to the labrinth from the external meatus, the chain ofauditory ussicles in the tympanic cavity is faster than the air in it. We haveexperimented calorically, preferably with both warm and cold water in the ears of the rabbits, to find out the relation between thermal irritation and the consequentnystagmus by use of the thermo-electric current.Apparatus and method of experiment.As to the apparatus used in the experiment, we made the thermocouples withone wire of copper and one of constantan, which were tied to the galvanometer.The apparatus was acculately described in our work “Sur la mesure de la temperaturede l'oreille externe.” We used, as test animals, medium-sized rabbits with normallabyrinthal reflex and broke a tymanic membrane in each of them to expose thelabyrinth on one side.We inserted a capillary tube of glass filled with vaseline into the fenestrarotunda of the exposed labyrinth and closed the entrance around the capillary tubewith vaseline. The temperature in the labyrinth was observed by inserting thethermo-coupie in the glass capillary tube.For thermal irritation of the external auditory meatus, we irrigated with cold (0°-10°) and warm (500-780) water. A thermometer was inserted through aswound in the dorsal muscle of the animal, care being taken to prevent bleeding asfar as possible.The temperature of the animal in the anus is so labile that we observed it in thedorsal muscle instead.