Abstract
There are a number of differences between the response to the passage of electrical currents through the head and the response of nerves to electrical stimulation. In the former cases responses occur only upon the continuous passage of current and not on the make and break. In the latter the response follows the transient not steady state of current. In the former alternating current or faradic current produces no response, in the latter they are effective stimuli. In the former the direction of response is related to the direction of current, not in the latter. Since stimuli of a duration of .000033 of a second at 15000 stimuli a second were effective to produce a response, if the vestibular nerve were being stimulated directly it would indicate that the irritability of the vestibular nerve was as great or greater than that of a motor nerve, which is unlikely.
Because of these observations we believe that the passage of a current through the head does not stimulate the vestibular nerve or its connections directly to produce falling or past pointing.
It is suggested that some physical change in the endolymph is produced by the passage of current through the head. Using rectangular shaped unidirectional current of variable periods as stimuli, it was found that when the interval was 1 to 1, falling occurred at 2.6 milliamperes, when 1 to 3, at 1.39 milliamperes, and 1 to 7 at 0.71 of a milliampere. It is pointed out that this change is not the production of heat or electrolysis since the current per unit is not a constant in producing falling or past pointing.
Using repetitive condenser discharges as the stimulus, we found that to produce falling or past pointing, when the voltage at which the condensers were being charged was kept constant as the duration of the intervals between stimuli was increased by diminishing the frequency of stimuli, it was necessary to increase the duration of the stimulus.
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