THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 571 



stages of degeneration. The blood-vessels in this zone also have their sheaths filled 

 with similar cells, but the numbers in the tissue spaces themselves are still too many 

 to allow the radial appearance to be recognised, which is characteristic of the areas 

 in which the blood-vessels radiating from the area have their walls filled with cells 

 which have passed from the tissue spaces to the lymphatic spaces of these vessels, 

 leaving the tissue more or less clear. In this transition zone, in addition to numerous 

 degenerating myelin fibres and vessels with rows of fat granular cells in their walls, 

 we find also a marked proliferation of the glia cells and protoplasmic processes, and a 

 widening of the normal glia meshes, but the degeneration of the myelin has not 

 advanced to the stage of complete disintegration and its absorption by cells. The 

 glia meshes of the adjoining normally myelinated tissue are distinctly widened, the 

 cells also enlarged, and the blood-vessels engorged and dilated. 



(ii) Similar " early " area in the cord — nerve fibres cut longitudinally (figs. 

 1, 2; 18-20; 326, 338). 



In Weigert sections under low power, this area is both laterally and at its upper 

 and lower limits very irregularly defined. The transition zone on all sides shows 

 that the fibres, though still staining with hsematoxylin, are markedly altered 

 (fig. 406). Longitudinal sections are very valuable in showing the changes in the 

 nerve fibre as it passes into the area. Those changes will be referred to in detail in 

 a later section. In the area itself are numerous globular and granular remains of 

 the myelin which have not undergone complete disintegration into fat droplets 

 (fig. 407), and one can also recognise, even within cell elements, such remains which 

 still retain the myelin stain. 



Marchi preparations (figs. 316-318) show the characteristic appearance of long 

 rows of fat granule cells, which seem to occupy the spaces left by the removal of the 

 degenerated myelin of the nerve fibre and also the longitudinally-running vessels 

 surrounded by elongated layers of similar cells (fig. 433). In sections stained with 

 Scharlach R. and hsematoxylin (figs. 18-20), the smallest capillaries can be followed, 

 marked out by a single or double row of such cells, the nuclei of which is either 

 central or pushed to the periphery by the accumulating granules of fat. In the 

 transition zones of the area the disintegration of the projecting nerve fibres can be 

 followed and the formation of the fat granule cells, which can be traced not only 

 into the transition zone but even between the nerve fibres of the normal tissue. 



In sections stained with diffuse stains, the large glia elements, already referred 

 to, are beautifully seen, lying often in rows (figs. 337, 379), with the nuclei of two 

 adjoining cells lying close to one another, as if they had arisen from the division of 

 one cell. The long branching protoplasmic processes extend round and almost 

 envelop the rows of fat granule cells, and in some parts the direction of these pro- 

 cesses is already becoming longitudinal. Almost pushed aside between the rows of 

 cells and the protoplasmic processes can be found faintly-stained, homogeneous, 



