616 DR JAMES W. DAWSON ON 



These, with the elements distinctly recognisable as proliferated from the endothelium 

 of the adventitial spaces and from the adventitial connective-tissue cells, together 

 with a few remaining fat granule cells or their nuclei, form the cellular content of 

 the vessel walls at this stage. Figs. 14 and 439 show beautifully the varieties of 

 the cells found in such a vessel. I have never seen any marked grouping of small 

 round cells analogous to the so-called " round cell infiltrations." As the sclerosis 

 advances the dissociated fibres of the adventitia gradually come together, and pro- 

 portionate to this is a gradual diminution in the contained cell elements (figs. 15 

 and 440). For a long time the outer adventitia] fibres form a recticulum which can 

 scarcely be distinguished from the peri-vascular glia reticulum, and in the meshes 

 are still found various cell elements. At a still later stage the sclerosis affects all 

 the parts of the vessel wall, and the dissociated fibrils form a fused, homogeneous, 

 almost hyaline layer. As the vessel becomes hyaline, the elastica becomes broken 

 up and lost, so that nothing can be recognised of specific muscle, connective tissue, 

 or elastic elements (figs. 440, 441 ). The relation of the proliferating glia cells to 

 the small vessels has already been emphasised, and at the later sclerotic stage the 

 proliferating fibrils, perpendicular to the vessel wall, form almost a radiating ring 

 around the vessel ; but very frequently, especially in cerebral areas, the new-formed 

 glia fibrils are laid down in concentric rings around the vessels (fig. 437). It has 

 also been mentioned, but may here be emphasised, that it is frequently the peri- 

 capillary glious zone in which the first traces of glia proliferation are noted. 



In the majority of the sclerotic areas all the vessels are condensed— arteries, veins, 

 and capillaries, — and it is not possible to draw any distinction between arteries and 

 veins, arterioles and venules (figs. 442-444). Similar condensation of the vessels 

 is found in all chronic sclerotic conditions in the nervous tissues, and Lugaro has 

 pointed out that this is in keeping with the small claims of their nutritive function, 

 for the sclerotic tissue requires less nourishing material. 



(b) Lymphatics. 



The increasing recognition of the importance of the lymphatic circulation in the 

 central nervous system has led to numerous researches upon the precise nature of 

 the lymph paths and the direction of the flow of the lymph within them. It cannot 

 be said, however, that any exact knowledge on either of these points has yet been 

 revealed. The present section of this paper is confined to the indications of 

 changes in the lymphatic vessel system in disseminated sclerosis. The lymph 

 apparatus shares in the changes in the blood-vessels, and Borst has strongly urged 

 the view that a disturbance in the lymphatic circulation is the essential factor in 

 the process underlying disseminated sclerosis. He points out that the factors which 

 bring about this disturbed circulation are alterations in the vessel walls and in the 

 meninges. Even slight affections of the former involve changes in the transudation 

 of the lymph and lead to pathological exudations, and even slight adhesion of the 



