THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 587 



which in size and structure closely resemble those found in the cord area (figs. 13, 

 361-3G3). These likewise develop in such profusion that soon the whole area is 

 permeated by them, and under low power the tissue appears fenestrated and areolar 

 — the spaces being occupied by round nucleated elements, and the intercellular spaces 

 being filled by large protoplasmic glia elements whose branching processes again 

 entwine around the cells. When the climax of fat granule cell development has 

 been reached, Weigert and iron-haematoxylin sections indicate the almost complete 

 absence of myelin within these areas ; the progressive changes in the nerve fibres 

 are not so easily followed as when the nerve fibres run only in one direction, but 

 both Weigert and Marchi sections show the characteristic appearances of an early 

 degeneration, the Weigert sections giving a myelin sheath diffusely or faintly stained, 

 and the Marchi, the different stages of its disintegration. At the stage of "fat 

 granule cell myelitis " the whole area is again beset with granular cells, both in the 

 tissues and in the vessel walls. Marchi preparations (figs. 68, 30 1) show the structure 

 and arrangement of these best, but cell stains, and Marchi sections counter-stained 

 with safranin, in which the fat has dissolved out of the fat granule cells — leaving the 

 skeleton structure of the tissue — show best the relation to the other tissue elements. 

 With the onset of the fibril formation, the walls of the blood-vessels, both within 

 the area and leading from it, are even more densely packed with fat granule cells, 

 amongst which may be found other nucleated elements, the result of the reaction of 

 the adventitia to the cells in its lymph spaces. It must again be emphasised that 

 it is areas at such a stage of development that have given the justification for 

 regarding the process as developing on the basis of an acute myelitis, for the cell 

 infiltration of the vessel walls and the presence of fat granule cells in such abundance 

 in the tissue gives all the appearance of a softened and infiltrated area. At an 

 earlier stage we have seen that the blood-vessel changes are not constant, and that 

 only on the onset of the removal of the fat granule cells in the lymphatics is there 

 any definite cell infiltration of the vessel wall. Later, as we shall see, the blood- 

 vessel changes again recede in their prominence. Figs. 362 and 365 give a clear 

 idea of the commencing fibril formation and the gradual separation of the fat 

 granule cells by the fibrils, and figs. 436 and 437 give a conception of the vessel 

 changes at this stage. 



The stage of advancing sclerosis is well represented by figs. 6, 363, and 366. It 

 will be seen in the low-power view that in a large area the sclerosis advances by 

 no means uniformly — small areas being present in which there is an almost dense 

 tissue, while others still contain numerous fat granule cells. The blood-vessel 

 changes correspond very closely to those described in the spinal cord area, and will 

 be more fully referred to in a later section. Weigert sections give a completely 

 negative picture within the area ; Marchi sections give a negative picture in the 

 sclerosed parts, but the fat granule cells are well brought out in the tissue spaces 

 and surrounding the blood-vessels. The further development of the fibrillar tissue, 



