THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 573 



changes in the nerve fibres as they pass into the affected area. The transition zone 

 is a very broad and irregular one, and can be more clearly understood from transverse 

 sections of such an area. 



Such an area, therefore, consists of elongated rows of fat granule cells, almost 

 alternating with rows of large, protoplasmic glia cells with long-branching processes. 

 In between the rows are numerous capillaries and larger vessels, cut mostly longi- 

 tudinally, and surrounded by one or more layers of fat granule cells. Numerous 

 axis cylinders have perished, and those persisting are markedly altered. There is a 

 complete absence of myelin within the area, and the transition into normal tissue is 

 a very gradual one. 



(ii) Small "early" area in cerebral white matter, with nerve fibres cut in 

 various directions (figs. 5, 6 ; 68 ; 361, 362). 



The most important and characteristic feature of such an area is the enormous 

 number of large cell elements. These are of two kinds : the one the round vacuolated 

 fat granule cell with central or peripherally -placed nucleus (fig. 365) ; the other the 

 large protoplasmic glia cell with branching processes (fig. 6). Both of these cell 

 elements are seen here at their most distinctive stage of development. This area 

 (fig. 5), situated in the central white matter at the base of one of the parietal con- 

 volutions, measured less than 2 millimetres in diameter. It was almost circular, 

 and was surrounded by a well-marked nucleated transitional zone. In Weigert 

 sections one saw a well-marked central engorged vessel with an increase of nucleated 

 elements in its walls, a complete absence of myelin within the area, and the presence 

 of numerous rounded spaces, almost equal in size, which gave the non-myelinated 

 tissue a very characteristic fenestrated appearance. With cell stains it was recognised 

 that these spaces are fat granule cells, so closely arranged together that one might 

 almost think of them as forming irregular tubular lines made up of cell units — the 

 tubules almost as closely arranged as the rows of liver cells in a lobule. Between 

 groups of these cells lie large glia cells such as are nowhere found in the normal 

 glial tissue. These are large cells with homogeneous cell body : their size sometimes 

 as large as that of a motor ganglion cell of the cord. They have large-branching, 

 protoplasmic processes which wind around the individual fat granule cells and almost 

 surround and isolate them. Their nucleus is large and vesicular, and contains a 

 very defined membrane and one or more deeply-stained nucleoli — its position is 

 usually excentric but is sometimes central. These cells differ from the Deiters or 

 spider cells only in degree and are pathological spider cells, and they may be multi- 

 nucleated. They are found specially numerous in the neighbourhood of the small 

 blood-vessels, and their processes are frecpiently attached to the adventitial wall 

 {cf. figs. 435, 436). With glia stains it is seen that the margins of the processes of 

 these cells are already becoming differentiated into fibrils (fig. 382) which are found 

 lying between and surrounding the fat granule cells. * The central vessel is dilated 

 TRANS. ROY. SOC ED1N., VOL. L, PART III (NO. 18). 81 



