566 DR JAMES W. DAWSON ON 



nerve fibres, and the granular appearance of the sclerotic area is reached. Sections of 

 such an area stained by the Marchi method again show no black staining : the charac- 

 teristic transverse section of the myelinated fibre is absent, but no traces of degenerat- 

 ing myelin are found either in the fine tissue spaces or around the blood-vessels. 



The impression is received that here again the normal architecture of the tissue 

 is preserved ; that the myelin sheaths have disappeared (fig. 258) (Weigert stain), 

 and have been replaced by a fine close fibre formation (fig. 354) (glia stain) ; that 

 the walls of the blood-vessels, even the small capillaries, have thickened walls with 

 few cell elements (fig. 440) (diffuse stains) ; that the axis cylinders have, at least 

 to a considerable extent, been retained (fig. 427) (silver impregnation stains) ; that 

 there are present in the area or its periphery no indications of the degeneration of 

 myelin (Marchi method) — thus allowing it to be supposed that the process which 

 caused the myelin destruction has come to a standstill ; and, finally, that there are evi- 

 dences at the periphery of the area, in a nuclear proliferation and diminution in myelin 

 fibres, of a process which has left these traces of a reaction to its further progress. 



These areas, just described, in longitudinal and transverse section, are typical of 

 the sclerosis which is the essential substratum of the disease known as disseminated 

 sclerosis. They show a compact glia fibril proliferation, apparently without spaces, 

 for only here and there are there traces of the original glia meshes. The area of 

 dense sclerosis is regularly surrounded by a peripheral transition zone, which inter- 

 poses between it and the healthy tissue. This transition zone shows very numerous 

 nuclei of small and large glia cells, with more or less developed glia trabeculte. 



(b) In the Cerebral White Matter. 



The first points to be noted in comparing such an area with a similar one in the 

 spinal cord are that in the brain it is much more usual to get a more defined outline 

 of the patch, and also that a central vessel, cut transversely or longitudinally, is 

 more frequently present. 



(i) Nerve fibres cut longitudinally, e.g. at the base of or within a medullary 

 ray (figs. 288, 372). 



The shape of the area is again often oval and its structure is very similar to that 

 described in the longitudinal direction of the cord. Weigert sections show again a 

 complete absence of myelin (fig. 284) ; the presence often of one thickened vessel, 

 which sometimes is found to extend centrally almost the whole distance of the patch 

 (fig. 287) ; and the presence also of numerous other smaller vessels cut transversely, 

 obliquely, and longitudinally — all with walls thickened, almost homogeneous and 

 structureless. The general substance of the area is again composed in great part of 

 fine glia fibrils (fig. 372), which run longitudinally and parallel to each other, and 

 surround the persisting axis cylinders (fig. 422). The glia cells in this area are, as a 

 rule, much less numerous than normal ; they have, however, more elongated and 



