THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 581 



a sheath with elongated meshes around the fat granule cells. On cross-section of 

 the nerve fibres it is difficult to trace this, but it can be seen that the fat granule 

 cells are gradually compressed by the increasing fibril formation between them. It 

 is probable that this compression aids the suction influence of the lymph flow in 

 drawing the fat granule cells out of the tissue spaces into the lymphatic spaces. 

 Many of the large protoplasmic glia cells are now found to have their protoplasm 

 entirely transformed into fibrils. Along with the increase of the fibrils and the 

 diminution of the fat granule cells in the tissue spaces, it is recognised that many of 

 the axis cylinders which have survived the swelling have now returned to their 

 former volume and are more readily recognised than at an earlier stage, lying in the 

 meshes of the condensing tissue. 



(5) The next stage, that of advancing sclerosis (figs. 11, 12, and 351), is one 

 which seems to occupy a long time. It is a gradual increase of the fibres, which 

 seem able to become more abundant, possibly through fibrillation, even after their 

 emancipation from the cell protoplasm. It is further a gradual diminution in size of 

 the glia nuclei, and an increasing withdrawal of the fat granule cells from the tissue 

 spaces, till only isolated examples are found. These may remain for a long time as 

 vacuolated or granular spaces in the dense tissue, their nuclei very crenated or lost, 

 and their membrane no longer recognisable. All the vessels, not only in the area, 

 but the vessels radiating from it into the adjoining tissue, have their adventitial 

 spaces crowded with similar cells. When the fibre formation has developed slowly 

 and regularly, the pathological increase has taken place, according to Weigert and 

 also in my experience, in a longitudinal direction, so that the transverse section 

 represents the glia fibrils as fine granules, which surround the remaining preserved 

 axis cylinders. Most of the glia cells have undergone regressive changes, but some 

 large examples are still found. 



(6) The final stage, that of complete sclerosis (figs. 353, 354), can scarcely be 

 separated from the former : its complete evolution must be a very slow one, but the 

 final result is a tissue which cannot be distinguished from that described under heading 

 1 , as an old sclerotic area. In this area no fat granule cells remain either in the tissue 

 spaces or in the vessel walls ; the glia nuclei are mostly small and may be fewer in 

 number than in the normal cord ; and the fine granular points, representing the 

 fibrils, surround the axis cylinders, giving the impression that a fine fibril formation 

 has taken the place of the degenerated myelin sheath. 



The blood-vessel changes, during the advancing sclerosis of the tissue, correspond 

 to a very gradual condensation of the vessel walls (figs. 442, 443). The fat granule 

 cells are gradually drained away, leaving the adventitial spaces still dilated. Many 

 of the nuclei of these cells are left, crenated or broken up, in the adventitial wall, 

 and add to its nuclear abundance. The numerous nuclei at this time may be 

 attributed to several sources, but the small round cells predominate. As the 

 surrounding tissue becomes more and more dense, all the walls of the vessel seem to 



TRANS. ROY. SOC. EDIN., VOL. L, PART III (NO. 18). 82 



