THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 567 



lighter-staining nuclei. Along with these many darkly-staining smaller nuclei are 

 found, which agree in form and staining with the normal small glia cells of the 

 cerebral white matter. The preserved axis cylinders are, as a rule, much fewer in 

 number than in the cord, and they show, even in the dense sclerosis, more evident 

 indications of a previous involvement. They are usually thicker, more diffusely 

 stained, and have more irregular contours as compared with the axis cylinders of 

 adjoining medullary rays. Marchi-stained preparations again show a complete 

 absence of any degerating myelin either in nerve fibre or in the presence of fat 

 granule cells. The affected area stands out much lighter in colour than the surround- 

 ing tissue, and gives a contrast almost as marked as the negative picture of the 

 Weigert section. In glia sections this condensed tissue is, on the other hand, much 

 denser and darker than the surrounding tissue, and its limits are often very defined 

 — that towards the central white matter being abrupt, that towards the radiations 

 of the convolutions being very frequently in the form of a wedge with its apex to 

 the radiations (cf. fig. 405). The transition zone at this limit is also much more 

 marked and consists of a narrower or broader zone of deeply-staining round nuclei, 

 amongst which a few larger, protoplasmic forms are found. This nucleated zone 

 extends for a short distance into the normal myelinated tissue. 



(ii) When the sclerosis affects a portion of the brain substance in which the 

 nerve fibres normally run in very varied directions (figs. 292, 293 ; 

 364 ; 397, 398 ; 430), e.g. a small defined area in the central white 

 matter above the roof of the lateral ventricle, the resulting tissue is 

 a very dense network in which the original glia spaces are replaced 

 by fine fibrils. 



On Weigert picro-fuchsin sections the central vessel stands out clearly as the 

 mid-point of a yellow-stained zone, at the periphery of which there is usually an 

 abrupt transition to normal myelinated tissue (fig. 294). If bundles of longitudinal 

 fibres are cut across, these often pass for a short distance into the sclerotic zone, 

 breaking the otherwise almost denned circular or oval outline of the area (fig. 292). 

 At their terminations such fibres do not show any evidence of degeneration but are 

 simply faintly-staining normal fibres. In this sclerotic zone there are found as a 

 rule, in addition to the central thickened vessel, several cross-sections of capillaries, 

 each standing out as a pink thickened ring, which encloses a narrow lumen. Indi- 

 vidual capillaries are quite obliterated and form a dense solid fibrous cord. Marchi- 

 stained preparations again show a complete absence of signs of disintegration of 

 myelin : the affected area again appearing lighter in colour than the normal tissue. 



Sections stained for glia and for cell structure show that the sclerotic tissue is 

 composed almost entirely of glia fibrils. These fibrils are very unequal in size : the 

 larger form larger meshes into which the finer fibrils cut and make finer meshes. 

 The tissue becomes denser and denser till the meshes are inconceivably fine (fig. 364). 



