THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 565 



At the periphery of the area, especially at its upper and lower limits, diffuse 

 stains bring out a zone where intensely-stained nuclei are in great abundance : these 

 nuclei, in iron-haematoxylin stain, are seen to occupy the spaces between the nerve 

 fibres projecting into the sclerotic tissue, and their increase can be traced for a 

 small distance among the fibres of the normal tissue on all sides. The glia fibril 

 proliferation and thickening of the vessels are here also evident, and this zone can 

 be looked upon as a zone of transition between normal and sclerotic tissue — a zone 

 where the pathological changes gradually cease till normal tissue is reached. 



(ii) Similar area in the cord with nerve fibres cut transversely (figs. 258, 259, 

 353, 354, 358-360). 



To understand the structure of such an area it must be remembered that in the 

 posterior columns, according to Weigert, the usual glia fibrils very largely run 

 longitudinally, and the pathological glia fibril formation takes place almost wholly 

 in this direction. Exceptions to such an arrangement will be noted later. When 

 the glia proliferation has taken the simple course represented in the former para- 

 graphs a transverse section of the areas seen in figs. 258, 259 will represent the 

 glia fibrils as minute fine points which more or less surround as a ring larger, more 

 diffusely stained, and more homogeneous points — the axis cylinders. If the section 

 is directly transverse to the direction of the fibres we get so dense a picture that, 

 under low power, no details can be recognised (fig. 354). But a higher magnification 

 shows that the normal meshes of the glia and the space originally occupied by the 

 myelin sheath of each nerve fibre is replaced by those fine points. Amongst them, 

 lying almost isolated and in no way forming the nodal points of a reticulum, are 

 rounded nuclei, with smooth nuclear membrane and clearer nuclear structure than 

 the small normal glia nuclei. In this dense tissue is found the cross-section of 

 numerous thickened capillaries and pre-capillary vessels (fig. 443). Around each 

 vessel is a narrow zone where the glia fibrils radiate almost perpendicularly to the 

 vessel wall — forming the " corona ciliaris " described by Borst and Storch. It is 

 not a question of a central vessel but of many transverse and oblique vessels. These 

 give the impression that not one single vessel, but the branches of a vessel system 

 are affected. Weigert sections show the complete absence of myelinated fibres 

 within the sclerotic tissue, but at the periphery the transition to normal tissue is a 

 gradual one — isolated well-stained myelin sheaths being found within definitely 

 sclerotic tissue (fig. 258). The transition zone is again seen to consist of a large 

 number of small deeply-stained nuclei, amongst which are found larger nuclei with 

 a distinct amount of protoplasm and several protoplasmic processes (fig. 357). Here 

 a more reticular arrangement of the glia fibrils can be recognised : the glia trabeculse 

 which, in the normal tissue, separate groups of nerve fibres, are in this transition zone 

 more evident, and the processes of the cells cut into the larger meshes, dividing up the 

 bundles into smaller and smaller groups, till, finally, the meshes contain only individual 



TRANS. ROY. SOC. EDIN, VOL. L, PART III (NO. 18). 80 



