[Experimental changes of the pH in the middle ear and its effect on the internal ear (author's transl)].

Irrespective of their highly differing pH-value many pharmaca are nowadays applied to the middle ear. Animal experiments are to answer the question, weather changes in the pH-value of the middle ear may cause internal ear damages, With local application of different buffers (2.3-9.1 pH) into the tympanic cavity, the membrane of the round window was examined by means of the surface preparation technique, the pH-value of the perilymph was measured and the hair cells of the organ of corti were counted and histologically evaluated. With the reduction of the pH-value in the middle ear from 4.0 to 2.3 an increasing damage of the round window membrane could be detected. The pH-value of the perilymph, however, showed only a slight statistical variation, which cannot be guaranteed. After multiple applications of extremely acid buffers into the tympanic cavity directly before the round window membrane, a small but statistically significant reduction in the pH-value of the perilymph could be noticed. Hair cell damages at the organ of corti could in no case be observed.