568 DM JAMES W. DAWSON ON 



The size of the glia cells varies very much, but the body of the cell is in general 

 round or slightly elongated and may contain one or more nuclei but little protoplasm. 

 Around the blood-vessels (fig. 398), even the capillaries, is a zone in which this fibril 

 formation is even more dense ; the fibrils rarely form a " corona ciliaris," but rather 

 concentric layers of fibrils closely pressed together, with few nuclei, form an outer 

 dense glious sheath to the vessel. The axis cylinder content of these areas has been 

 exceedingly difficult to ascertain, for the brains of most of the cases in which such 

 areas occurred were already fixed in formalin, and the Bielschowsky impregnation 

 method in cerebral areas gave no absolutely reliable results. A comparison with 

 other areas, stained by means of Cajal's silver method, showed how extremely 

 difficult it was to differentiate between glia fibrils and fine axis cylinders and their 

 branches. The intimate network formed by both is so alike that it was never 

 possible to be satisfied that in these dense sclerotic cerebral areas there could be so 

 abundant an axis cylinder network persisting, and the conclusion was come to that 

 in such areas the glia network had been stained. Other areas which had been cut in 

 two by the section of the hemispheres were taken through — one part by Cajal's 

 method, and one for glia and cell staining. These showed that when the fibrillar 

 network of the glia was not quite so dense as above described, there was a very 

 abundant network of axis cylinders and their finest branches persisting (fig. 430). 

 Such areas will be referred to in a later section. 



The nucleated transition zone of these dense sclerotic areas was, as a rule, a 

 narrow one, and the nuclei were all relatively small and darkly staining (fig. 403). 

 Even in the sections stained with diffuse stains the contrast between the sclerotic 

 tissue and the normal was very evident. 



Such areas, therefore, consist of a dense-meshed fibrillar tissue, poor in nuclei, 

 with thickened vessels. The areas give the impression again of tissue in which the 

 normal architecture is retained : they also seem to show that the change consists in 

 a demyelination, a complete substitution of the spaces by fibrillar tissue — which in 

 its arrangement forms simply a condensation of the original glia meshwork (fig. 364), 

 a thickening of the walls of the vessels originally present in the tissue (fig. 440), and, 

 finally, the formation of a narrow but dense nucleated peripheral zone (fig. 403), 

 which forms the transition to normal tissue. 



2. An "Early" Area, 

 (a) In the Spinal Cord. 



(i) Nerve fibres cut transversely (figs. 10 ; 260, 261 ; 66, 313 ; 350), e.g. in 

 the middle or anterior third of the posterior columns. 



On Weigert sections an irregular non-medullated area can be recognised (fig. 260), 

 which extends approximately from the middle of the posterior median septum 

 forwards to the posterior commissure. The area is, roughly speaking, triangular in 



