5.34 DR JAMES W. DAWSON ON 



ally, and within each a blood-vessel, cut longitudinally or transversely, could be 

 traced, surrounded by a delicate peri-vascular space. Microscopically the pia of both 

 brain and spinal cord was thickened, and all the vessels, especially the arteries, were 

 also thickened : the vessels within the areas were hyaline and often obliterated, 

 especially the paracentral vessels. Outside the areas the blood-vessels were 

 also thickened and their lumen narrowed. In several cases the thickened vessel 

 was the apex of an oval area. There was frequent marked glia proliferation around 

 the central canal. Borst specially emphasises the presence of cystic spaces, often even 

 macroscopically evident, around the obliterated vessels : these spaces were lined by 

 cubical epithelium, probably arising from the glia, in virtue of its origin from the 

 ependymal epithelium. These cystic spaces were regarded as having undoubtedly 

 arisen in relation to the obliterated vessels, and, apparently, first as delicate peri- 

 vascular spaces : they were, therefore, an expression of the obvious congestion of the 

 lymph circulation. 



As a further expression of this congestion there were found disseminated areas, 

 usually round or oval and distinctly circumscribed, within which there was a rare- 

 faction of the myelin constituents of the nerve fibres, while the axis cylinders remain 

 naked. The glia in these areas is very delicate, and the glia cells are transformed 

 into large protoplasm-rich forms. Such areas are described as " Lichtungsbezirke," 

 are ascribed to a hyperlymphosis of the tissue, and are looked upon as a fore-stage of 

 the sclerosed areas. When the increased pressure of the lymph is removed, the glia 

 undergoes proliferation and invests the persisting axis cylinders with a more or less 

 dense fibre feltwork. The proliferation of the glia need not always be solely a 

 substitutive process which arises in consequence of the degeneration of the myelin : 

 the existing hyperlymphosis may act as a stimulus to the glia, causing an inflam- 

 matory glia proliferation. 



What the final cause is which acts on the membranes and the vessel walls, Borst 

 concludes must be mere conjecture. The virus, in acute infections, courses in the 

 first place in the blood, and from it passes through the walls of the vessel, causing an 

 arteritis and a peri-arteritis in more or less intense degree. According to the degree 

 of the lesion produced in the vessel we get abnormal permeability, diminished 

 resistance to the oscillations of blood-pressure, and paralytic dilatation. Later, 

 owing to a longer-acting irritant, the vessel changes assume a more or less productive 

 character and express themselves chiefly in thickenings of the vessel wall and 

 narrowing of the lumen. Through these processes in the vessel walls occur 

 circulatory and nutritive disturbances. Borst's view is, therefore, an extension of 

 Rindfleisch's view ; he ascribes to the influence of the disturbed lymph-circulation 

 the origin and extension of the process, but the changes in the vessel walls give 

 occasion to the existence of the lymph-congestion. 



Arndt (1875) had, previous to Borst, laid emphasis on the influence of lymph- 

 congestion in the production of areas of " grey degeneration." Arndt looked upon 



