On the degeneration of the neurone / [Sir F.W. Mott].

  • Mott, F. W. (Frederick Walker), 1853-1926
Date:
1900
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Licence: In copyright

Credit: On the degeneration of the neurone / [Sir F.W. Mott]. Source: Wellcome Collection.

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    the myelin to the formation of fat within a fat cell. Vignal’s description of the process of myelination is as follows: At a particular stage of development, when the nerve-fibre consists of non-nucleated bundles of fibrils, mesoblastic cells migrate into the interior of the fibre and apply themselves closely to single groups. Their cell protoplasm increases in length and in breadth until some of the primitive fibrils are enclosed. The definite intervals in the enclosing sheath, corresponding to the nodes of Eanvier, coincide with the spaces between the ensheathing cells ; consequently each internode represents a segment of the continuous axis-cylinder wrapped round by a mesoblastic cell. At the same time, according to Yignal, the myelin appears in the cell protoplasm in the form of minute droplets ; these become more numerous and run together to form a general thin covering of the axis-cylinder. Vignal does not deny the possibility that the axoplasm may share in the formation of the myelin, but in quite a subordinate manner. The observations of Boveri, which recently have been confirmed by Bethe,35 show that the sheath of Schwann is reflected inwards at the nodes along the axon ; if this be true there is (as in a serous membrane) a parietal and central layer, and between the two the myelin is contained. This would prove Yignal’s hypothesis. Gurwitsch has studied the development of peripheral nerves in embryo sheep, fixing the sciatic nerve with Apathy's solution and employing various staining reagents used by that observer. He came to the conclusions : (1) that the nerve-fibre is a prolongation of the ganglion cell; (2) that the sheath of Schwann arises from the surrounding mesoblast; and (3) that the myelin sheath has nothing in common with the sheath of Schwann, and probably arises only as a product of the metabolism of axoplasm. Time will not allow me to give you more than this very brief outline, and to those who are further interested in the subject I would refer them to an admirable digest on the “ Histology and Pathology of the Nerve-cell,” by Ford Robertson,30 or to the splendid new work of Barker on the “ Nervous System.” It would take too long here to describe the normal structure 33 Loc. cit. sn i< Normal and Pathological Histology of the Nerve-cell,” Brain, 1899 Part lxxxvi.