1913 The Lancet  
630 'segmental cell; the myelin is similarly differentiated in each segmental cell ; the outer layer of protoplasm forms the sheath of Schwann ; there remains a thin zone of undifferentiated protoplasm between the myelin sheath and the neurilemmal sheath, which with its nuclei represents the living element of the cell, while, properly speaking, the differentiated parts have no life of their own, and disappear under pathological conditions. It will be seen that .according to this view there is a
more » ... his view there is a close analogy, which Durante has emphasised, between muscle and nerve -elements. At present opinion is divided among embryologists as to the actual method of development of nerve fibres, some holding the theory of budding from a central cell, others holding the opinion that cell chains are formed. Similarly, there are differences of .opinion in regard to the genesis of the nerve fibres of the central nervous system, and as it is widely recognised that the manner of regeneration of any tissue closely follows the manner of its first development, we meet with the same diversity of views as regards the histogenesis of nerve regeneration. A very important contribution to the solution of this vexed question has been made in a paper recently issued in the Transactions of the Royal Society of Edinburgh, written by the late Dr. Alexander Bruce, of Edinburgh, and Dr. James W. Dawson.' t A young woman aged 30, whose symptoms during life had been those of an anomalous spastic paraplegia, died in a state of great ,emaciation, and subsequent examination showed that in the :spinal cord substance itself, scattered through its whole ength except in the upper cervical segments, were enormous BTrmbers of small nodules which were found to be pure neuromata, consisting of whorls of medullated fibres, always in relation to vessels, and completely separated off from the normal card substance round them. Further, the spinal pia mater was infiltrated throughout with innumerable abnormal medullated fibres ; they were so numerous in the pia of the lumbo-sacral cord that the whole circumference of the membrane was seamed with strands of from 4 to 12 fibres cut longitudinally or obliquely or transversely, and in the adventitia of the pial vessels they formed an encircling iieticulum. Nodules were also found in the medulla oblongata and pons, but they presented this important and interesting difference, that the fibres within them were not myelinated ; most of them showed a network of interlacing fusiform cells, but one or two were evidently of the nature of an intermediary link with the neuromatous nodules of the cord. Other anomalies in this remarkable case may be here passed over, in order to direct attention to the interpretation drawn by the authors from a consideration of their material. They have made out that the nodules consist of fusiform cells, of nucleated proto: plasmic tubes, and of myelinated nerve fibres, and they have been able to trace the first of these uniting up in chains to form the tubes, in which, again, they have seen division into interannular segments with laying down of myelin and .differentiation of an axon. They are of the opinion that fusiform cells linked on to one another have formed embryonic merve fibres, in which the specific nerve elements of axon and. myelin sheath eventually appear. Apparently the <original fusiform cells or neuroblasts have at a very early period in the foetal life of the patient wandered into the site of development in the mesoderm of the vessels and connective tissue constituents of the spinal cord. It will be realised, then, that this
doi:10.1016/s0140-6736(00)75474-2 fatcat:rd7vjnouc5c6lcl23duroq3cza