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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![semicircular canals are associated with the development of serous labyrin¬ thitis and are not related to the nerve degeneration. It was pointed out, for instance, that the cochlear neurone may have completely disappeared, and yet in the absence of serous labyrinthitis the organ of Corti may appear normal or nearly normal. Finally it may be asked, how do these vitamin A-deficient diets produce all these changes in the labyrinthine capsule? This question cannot be answered at present, but it is already clear that the answer must include not only consideration of the auditory mechanism but of the many other nerves in the body. Although it is probable that over¬ growth of new bone holds the secret to the sequence of pathological changes, in the cranial nerves at least, this part of the subject has not been sufficiently investigated to allow a full description to be given, except in the case of the auditory nerve. On the other hand, a fairly complete survey of nerve degeneration produced by these diets has been worked out in the case of the dog and rabbit [Mellanby, 19346, 1935], and it is now necessary to see whether all such degenerative changes in the spinal cord as well as the brain can be related directly or indirectly to over¬ growth and pressure of bone. Whether this is so or not, it is already evident that overgrowth of bone in young animals due to vitamin A deficiency does not affect all bones. In the long bones the absence of vitamin A probably affects the texture of the cancellous tissue but it does not appear to alter the shape of these bones. In view of the historical development of knowledge of bone growth, especially in regard to rickets and the discovery of the calcifying vitamin D, it is of peculiar interest that vitamin A, with which vitamin D is so often associated, should also be concerned with bone formation. The parts played by these two vitamins are, however, essentially different. In the absence of vitamin D there is overgrowth of osteoid tissue in all growing bone. In the absence of vitamin A there is overgrowth of apparently normally formed bone in certain places. In view of the growth-promoting function usually assigned to vitamin A, it is of interest to note that its presence in young dogs prevents overgrowth of the labyrinthine bone. It would be fruitless at this stage to conjecture the nature of the mechanism whereby vitamin A works in limiting the growth of bones at the base of the skull and other places to their normal shape, so that in its absence these bones overgrow and destroy the nerves. It is certain, however, that the explanation of this mechanism must depend on interesting physiological processes, of whose nature nothing is known at the present time,](https://iiif.wellcomecollection.org/image/b30631087_0025.jp2/full/800%2C/0/default.jpg)
