590 DR JAMES W. DAWSON ON 



of the glia meshes. This is only in small part due to the retraction under the 

 influence of hardening agents. The abnormal dimension of the interstices points to 

 the presence of liquid in excess in the tissue. A primary degeneration of the nerve 

 elements, at least of the myelin sheath, as an explanation of " areolar " areas, has been 

 assumed by those who see in such areas a proof of the change in the myelin sheath as 

 the essential and primary feature of disseminated sclerosis. It is not denied that later, 

 if there is time, a proliferation of the glia may be associated. On the other hand, 

 Redlich and others see in " areolar" areas a process quite distinct from the essential 

 substratum of a typical sclerotic area. 



It must here be added that very large numbers of the areas found in all the 

 cases, especially cerebral areas in which the process was quite stationary, as far as 

 the degeneration of the myelin at the periphery was an indication, showed under 

 low power a much less dense sclerosis than that described as compact sclerosis. In 

 such areas fat granule cells were absent both from the tissue spaces and the vessel 

 walls ; Marchi and Weigert sections also gave a completely negative picture, but cell 

 stains and glia stains showed that numerous large, multi-nucleated glia cells were still 

 present, and that each was the central point from which a marked fibril formation 

 radiated. This fibril formation, however, had not been sufficient to form the inex- 

 tricable tangle of the denser areas, and yet was quite distinct from the simple 

 distension of original glia meshes of the areolar areas (figs. 367, 368). We thus 

 draw a sharp distinction between these two forms, which have both received the 

 name of " areolar" areas, and reserve this name for the areas in which the original 

 glia meshes are retained or distended, and reserve "areolar zone" for the zone 

 sometimes found around compact areas, which has a similar structure. 



(b) Peri-vascular Sieve-like Areas. 



Non-myelinated areas are frequently found, especially in the brain, in which 

 large open spaces are met with around all the vessels found within the affected 

 area. The wall of this space is, on the side of the nerve tissue, represented 

 by a dense ring of glia fibrils, often with very few nuclei. The walls of these 

 vessels seem often little modified : they may be slightly thickened and infil- 

 trated, but the essential change is a separation of the constituent elements of 

 their adventitial sheath so that the connective-tissue fibrils stretch across and 

 form a very wide-meshed reticulum between muscle coat and condensed glia 

 (figs. 448-450). Within these meshes a fine coagulum (fig. 441) is frequently 

 found, together with a few cells, often containing pigment or the remains of fat 

 granule cells. The vessels thus affected lie together in groups, and give the tissue 

 a sieve-like character, which, when advanced, has been termed " l'etat crible." The 

 impression is received that it is the branches of one vessel stem (fig. 448) that are 

 concerned in this change. Around each vessel the myelin fibres are dissolved, the 

 glia meshes are widened, and both large and small glia cells are proliferated 



