Lesions of the central and peripheral nervous systems produced in young rabbits by vitamin A deficiency and a high cereal intake / by Edward Mellanby.

  • Edward Mellanby
Date:
[1935?]
Catalogue details

Licence: In copyright

Credit: Lesions of the central and peripheral nervous systems produced in young rabbits by vitamin A deficiency and a high cereal intake / by Edward Mellanby. Source: Wellcome Collection.

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    are seen in the axis cylinders of the nerves of rabbits fed on carotene- deficient diets before advanced myelin degeneration occurs. In order to determine the position of complete disappearance of groups of nerve fibres, Kulchitsky’s modification of the Weigert-Pal method was adopted. Observations on the Histological Results obtained by the above Methods. When examining nerve fibres most attention was fixed on the myelin sheath and the changes it was liable to suffer under the prescribed experimental conditions. It is well known that histological methods for demonstrating demyelination changes, especially those involving the use of osmic acid, are apt to give unreliable results unless examined very critically. A great effort was made to avoid wrong interpretations of the experiments owing to misleading pictures ; most of the animal experiments were repeated many times : the tissues from each animal were in many cases stained by several methods, and, when adopting any given technique for unknown tissues, sections of material known to be normal were often carried through simultaneously. When the animals are severely affected there is no difficulty in demonstrating degenerative changes in the nervous tissues ; when, how¬ ever, the effects are slight it is by no means easy with the methods at present available. In early cases only two or three scattered fibres in a tract may be grossly changed ; sometimes, for instance in the posterior roots, none show typical Wallerian degeneration, that found being rather of the annular type (see Plate VI, fig. 3). In this form the fibres are swollen, the myelin is altered in chemical composition but is not yet disintegrated, so that in cross section stained by Marchi’s technique axis cylinders are seen surrounded by a dark ring of altered myelin stained with osmic acid. This annular type of degeneration is commonly found in the peripheral nerves of rabbits fed on carotene-deficient diets, but more rarely in the central nervous system. There is evidence that nerves so affected can be brought back to normal fairly rapidly when the deficient nutritive agent, in this case vitamin A or carotene, is supplied to the animal. This point, which I have discussed elsewhere [1 (e) (/)] in relation especially to degenerative changes in the ophthalmic division of the fifth nerve in cases of xerophthalmia, is one demanding much closer study both because of its scientific and its practical interest. When the degeneration is more advanced and the myelin sheath has disintegrated, structural recovery takes a much longer time.