THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 569 



shape, with its base to the commissure, and under low power has a more or less 

 definite sinuous outline. At the periphery on all sides there are isolated nerve 

 fibres passing for a short distance into the area, and under high power it is seen that 

 their myelin ring is very thin, or stains diffusely, and shows evident signs of degenera- 

 tion. This area has formed with the posterior median septum and its vessels as a 

 centre (fig. 313), and on either side are found numerous cross-sections of small vessels 

 and capillaries and longitudinally-running branches of the posterior median fissure 

 vessels. Individual branches of these longitudinal vessels can be followed up into 

 the surrounding normal tissue. The tissue of this area, even in Weigert sections, is 

 seen, notwithstanding the absence of myelin and the presence of changed vessels, 

 not to correspond to the dense sclerotic fibrillar tissue seen in the former area 

 described. The blood-vessels — arteries, veins, and capillaries — are all dilated and 

 engorged with blood, and their walls, instead of the homogeneous, thickened, 

 structureless tissue, show in the intima and media little recognisable change from 

 normal ; but the adventitia has its lymphatic spaces dilated and filled with nucleated 

 elements, and these same nucleated elements are scattered irregularly through the 

 non-myelinated tissue, and in the blood-vessel walls of the transition zone (fig. 10). 



The most characteristic features of this area are seen best with diffuse stains. 

 Hsematoxylin and eosin, or Van Gieson's stain, or, even better, Heidenhain's iron- 

 hsematoxylin stain, show the presence of a very large number of nucleated cell 

 elements with a considerable amount of protoplasm. Most of these large cell elements 

 correspond roughly to pathological examples of the proliferated spider cells of the 

 normal tissue (fig. 9). The nucleus is large, vesicular, with a very light chromatin 

 framework, and one or more distinct nucleoli. It lies usually excentrically in the 

 protoplasm : this is large in amount, usually homogeneous, and stains slightly with 

 haematoxylin, or yellowish green with the picro-fuchsin. From the protoplasm 

 radiate in all directions very fine branching, protoplasmic processes, which break up 

 into a fine network. Many of these cells are multi-nucleated, and vary greatly in 

 shape and size from star-shaped forms to those with crescentic outline and bi-polar 

 forms. Their processes bear very frequently a very definite relationship to the 

 vessel walls — a relationship which will be more fully emphasised when describing 

 recent areas in the cerebral white matter. Smaller and darker-stained nuclei, with 

 little protoplasm and no processes, can also be found in considerable numbers. In 

 the spaces formed by the large branching processes of these cells and in the 

 adventitial spaces of the blood-vessels lie the second tissue elements characteristic 

 of such an area. These are larger, rounded, nucleated cells, with a large amount of 

 vacuolated protoplasm : they correspond to the phagocytic cell of the central nervous 

 system, and their vacuolated appearance is derived from the solution of the fine 

 degenerated myelin granules in the process of hardening. NiSSL has given to these 

 cells the name " Gitterzellen " from their morphological appearance, but they are more 

 generally known as compound granular or fat granular cells (" Fettkornchenzellen ") 



