The experimental production of deafness in young animals by diet / by Edward Mellanby.
- Edward Mellanby
- Date:
- [1938?]
Licence: In copyright
Credit: The experimental production of deafness in young animals by diet / by Edward Mellanby. Source: Wellcome Collection.
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![twists the internal auditory meatus, so that it may be impossible to get a complete section of the nerve in one histological preparation, as can usually be done in normal animals. This twisting of the internal auditory meatus must also stretch the nerve. New bone may also occasionally be seen in a third place, namely in the scala tympani at the basal whorl of the helix. The inconstancy of the small amount of bone in this third position indicates that it is probably inde¬ pendent of the other two masses of periosteal bone and may rather be related to serous labyrinthitis. The general result of this investigation, therefore, is that a deficiency of vitamin A in the diet has resulted in the development of newly formed bone and the degeneration of the 8th nerve, especially the cochlear neurones. As a rule, the greater the bone formation, the greater the degeneration of the nerves of the labyrinth, and the conclusion that the nerve degeneration is due to mechanical interference produced by bone overgrowth is difficult to avoid. This deduction is supported by what is already known of the reaction of each division of the auditory nerve to injury of their central branches. If the cochlear nerve reacted as do most sensory nerves to injury of its central branch, it would not be expected that the cells of its spiral ganglion and their peripheral branches should be so easily destroyed by mechanical influences bearing on its central branch in the internal auditory meatus. It is known, however, that the cochlear nerve is unlike most other sensory nerves in this respect and is even unlike the vestibular division. For instance, Wittmaack [1911] showed that destruction of the central branch of the 8th nerve in the internal auditory meatus with preservation of the blood supply caused degeneration of the cells of the spiral ganglion with their peripheral branches to the organ of Corti. Wittmaack also found that the peripheral vestibular branch and Scarpa’s ganglion did not degenerate after this operative procedure, although the central branches of the vestibular nerve were destroyed. These results have been confirmed by Kaida [1931], by Hallpike & Rawdon-Smith [1934] and Hallpike [1938]. Other confirmation comes from the observations of Crowe [1929], corroborated by de Kleyn & Gray [1932], that pressure upon the 8th nerve by a tumour in the internal auditory meatus leads to degeneration of the peripheral cochlear neurone. These facts show that the degenerative reactions of the cochlear nerve represent a notable exception to Waller’s law. It is clear, also, that the condition of the cochlear neurone in the present work is in keeping with its degeneration being due to pressure and stretching of the central fibres by the newly formed bony masses.](https://iiif.wellcomecollection.org/image/b30631087_0022.jp2/full/800%2C/0/default.jpg)
