THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 589 



4. Other Types of Areas. 



So far the histological description has been confined to areas which may be looked 

 upon as typical of a late and of a recent process respectively, and to the evolution of 

 a sclerotic area, on the one hand by a gradually increasing hyperplasia of the glia, 

 and on the other by stages which include the formation of a large number of fat 

 granule cells. As different stages occur in the same case, and as the process by no 

 means always follows the same uniform course of development, it will be evident 

 that the histological picture met with is a very varied one. Yet before a com- 

 prehensive view of the complete process can be obtained, it is necessary to add 

 to this complicated picture a brief description of other areas — areas so frequently 

 met with as to constitute types almost as definite as those already taken of an 

 old and a recent process. 



(a) Areolar Areas. 



The " areolierte " areas of German writers. At first sight it would be 

 natural to relate such areas simply to an arrest of the fibril formation before a 

 dense sclerosis had taken place. An examination of the transition zone around 

 most of the old areas, where the process has become stationary, and yet the fibril 

 formation is not so abundant as in the centre of the area, would seem to justify 

 this explanation. A close examination, however, shows that this cannot be accepted 

 as the constitution of all such areolar tissue. Under a high magnification the glia is 

 found to be often relatively unaltered, and to show only a distension of the network. 

 Wide meshes are thus formed, with cells at the nodal points of the network, and 

 frequently larger spaces result from the opening into each other of adjoining meshes 

 by the breaking down of the glia fibres separating them. Within the meshes the 

 myelin sheath has disappeared, leaving the axis cylinder at one margin, or this also 

 has disappeared, and the space is empty, or contains only granular remains of 

 regressively changed fat granule cells. An area of dense glial sclerosis is frequently 

 quite completely surrounded by such a peripheral areolar zone, which interposes 

 between it and the healthy tissue. This peripheral zone contains numerous nuclei 

 and dilated vessels, with nuclear accumulations in their dilated adventitial sheaths : 

 its mode of formation is to be distinguished from that of the transition zone already 

 described — the latter being distinctly an arrest of the development of the fibrils 

 before complete sclerosis had occurred, while this areolar zone around a compact area, 

 and the areolar areas described in this paragraph, are to be traced in all probability 

 simply to an acute and rapid degeneration of the nerve elements, with a distension of 

 the original glia meshes before fibril formation had occurred. In the spinal cord 

 such a distension of the glia meshes, swelling of the myelin, and distension of the 

 adventitial lymph spaces of the vessels, extends sometimes over the whole transverse 

 section of the cord. At other times at the periphery of the cord we get a widening 



TRANS. ROY. SOC. ED1N., VOL. L, PART III (NO. 18). 83 



