584 DR JAMES W. DAWSON ON 



(ii) Spinal cord area — nerve fibres cut longitudinally. 



The series of drawings (figs. 1-4) and photographs (figs. 325-336 and 337-342) of 

 a part of an area in the posterior columns cut in longitudinal direction almost suffi- 

 ciently indicate the nature of the changes. A glance at these figures .shows the two 

 outstanding features of the earlier process : the development (l) of an enormous 

 number of large glia cells with a wide zone of protoplasm and numerous branching 

 processes which quite mask the outline of the cell body, and (2) of rows of fat granule 

 cells which tend to occupy the position of the degenerated myelin tubes. The latter 

 figures show (l) the gradually increasing fibril development at the expense of the 

 glia cell protoplasm and processes, (2) the increasing diminution of the fat granule 

 cells in proportion to the increase in fibrils, and (3) the presence of large numbers 

 of axis cylinders in this fibrillar tissue. 



Here also the first change visible is an enlargement of the protoplasmic processes 

 and nucleus of individual spider cells. This is closely followed by a swelling both of 

 myelin sheath and axis cylinder, both of which swell out to occupy the whole space 

 of the distended glia meshes, without, however, breaking through the glia reticulum 

 which forms the meshes. Together with this change in axis cylinder and myelin 

 sheath is an increase in the number of the normally present small glia nuclei, which 

 may be seen, often in short rows, lying between the swollen nerve fibres (fig. 325). 

 It is in such a section that it is possible more easily to follow the gradual increase in 

 size of these cells and their development into the first fat granule cells, which lie 

 closely applied to the swollen and degenerating myelin sheath. At this stage 

 numerous dilated longitudinal capillaries and larger transverse and oblique vessels 

 can be recognised in the affected tissue. 



The development of the large spider glia cells occurs pari passu with the develop- 

 ment of the small glia nuclei, and long rows of hypertrophic cells (fig. 379) of very 

 varying shape may now be found, their long-branching processes passing in between 

 the degenerating nerve fibres. The increase in the formation of fat granule cells 

 takes place in a very close relation to the number of the degenerating fibres, and 

 soon the whole tissue is composed of these rows of the two cell elements, pushed 

 aside amongst which may be found very swollen axis cylinders or granular remains 

 of such (figs. 1, 32G, and 338). 



The stage of " fat granule cell myelitis " has now been reached, and the description 

 of the early area described under heading 2 applies to this area. The further evolution 

 to the old sclerotic area described under heading 1 consists in the further development 

 of the fibrillar glia tissue already described in transverse section. Here, however, it is 

 much more easily recognised how the fibril formation tends to take place in a longi- 

 tudinal direction. When the tubular rows of fat granular cells are fully formed, the 

 glia cell processes twine around them and, when the fibril formation commences, the 

 fibrils not only form between the rows, but pass in transversely or obliquely between 



