[Sound sensations produced by electric stimulation of the structures of the middle ear and the tympanic chord].

Certain facts must be clearly understood before any attempt is made to analyse the sensations produced by electrical stimulation of the structures of the middle ear. Firstly, when the current passes from an electrode to the skin or to any polarised structure whatsoever, the point at which the electrode is applied and the skin behave like the two plates of a condenser microphone. Electrical vibrations are transformed into ordinary acoustic resonances which can travel through air or bone. These acoustic resonances are fairly pure in comparison with electrical vibrations, judged by the standards under investigation. If a continuous polarisation potential, which gives better distribution of the electrical charges, is added, the capacity of the microphone is increased and greater purity obtained. Consequently, the quality of sound heard in this way depends not only on the quality of this electro-physiological microphone but also on the quality of the internal ear. The acoustic effect produced in this way is called an electrophonic effect. Stevens, Jones and Flottorp described this. Therefore an internal ear which has lost the ability to hear high-pitched sound cannot hear them by means of this electrophonic effect any more than it can by ordinary auditory stimulation. Stimulation of the skin of the mastoid and of the external auditory meatus can be sensed by means of this electrophonic effect. Next, sensations recorded by means of direct stimulation of the acoustic nerve (DJOURNO and EYRIES) or by implantation of intra-cochlear electrodes (SIMMONS, DOYLE, MICHELSON) were studied. Sounds heard through stimulation of the structures of the middle ear should be analysed in the light of these findings and bearing in mind that very strong stimulation of the promontory or of the auditory meatus always causes an auditory sensation without frequency awareness due to global stimulation of the acoustic nerve (faciaestations appeared when experiments, the results of which are described, were carried out, although there is a possibility of episode vestibular irritation. These stimulations were in fact always very weak. Our results were analysed in relation to the quality of the internal ear: completely deaf, serious condition, internal ear normal. The impulses were provided by a direct current battery: these were square with a frequency of between 50 and 900 Hertz, a tension of 0 to 8 volts per 1/10 volt. The electrode was bipolar. The experiments were monitored from time to time by oscilloscope. Mention should be made of the technical and psychological precautions to be observed when stimulation of this kind is carried out if results of any value are to be obtained: a relaxed, sensible patient with whom one can communicate easily. Not much can be gathered from a person deaf in both ears. With the ear opened, the posterior part of the tympanum pulled forward, stimulation of the round window always results in production of a sound at a threshold of 0.5 to 2.5 volts.