Abnormal mineral deposits from the membranous labyrinths of deaf Dalmatian puppies were examined microscopically. Most such deposits were located on the saccular otoconial membrane and were associated with collapse of the saccule and of Reissner's membrane. In both ears of one pup, crystals resembling otoconia were found on the surface of the stria vascularis. In two others, grossly abnormal crystals were seen on the utricular otoconial membrane, and in one of these crystals were also attached to the cupula of the left horizontal canal. In four animals the tectorial membrane was calcified. Most deposits consisted of apatite spherulites, but large multiple crystals (probably of calcite) were occasionally present. Some of the abnormal mineral deposits in the Dalmatian closely resemble those found in man, and they may originate in the same way.
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