588 DR JAMES W. DAWSON ON 



at the expense of the glia cell protoplasm, and the gradual removal of the remaining 

 fat granule cells, leads to the formation of a dense sclerosis, the meshes of which are 

 so fine that under low power almost no spaces can be recognised (fig. 364). Within 

 this area the glia nuclei gradually diminish in size and number, and, finally, they are 

 fewer than in the normal tissue of the neighbourhood. Both Weigert and Marchi 

 sections give a completely negative picture of such an area — the areas standing out 

 clear against a dark background (figs. 292-294, 397). Glia stains, on the other hand, 

 give a dense positive picture — the area standing out deeply stained against a lighter- 

 stained background (figs. 398 and 401). 



The transition zone of such areas must now be referred to. Here, also, we have a 

 gradual but slower evolution of the same changes as within the area, but the sclerosis 

 never reaches the stage of a final, dense meshwork. In this transition zone are found 

 at successive stages degenerating myelin fibres, with hyperplastic glia cells and fat 

 granule cells both in the tissue and in the vessel walls — signs of an advancing process, 

 which frequently remain long after the sclerosis within the area is complete. When, 

 finally, all indications of myelin degeneration have been removed, the transition zone 

 is markedly different from the adjoining sclerotic tissue on the one side, and the 

 normal tissue on the other — from the former in the lesser degree of glia fibril forma- 

 tion, and from the latter in the diminished number of myelin fibres, and the thinness 

 of the ring of myelin around such as persist in this zone. Again, as in the cord 

 area, there is a marked small glia cell proliferation in this transition zone (fig. 403), 

 together with a few enlarged glia cells (fig. 404). The latter may also be found 

 extending for a short distance into the surrounding, otherwise healthy tissue. In 

 this description of the evolution, few references have been made to the persistence 

 of the axis cylinders. Nowhere is the distinction more difficult to draw between 

 glia fibrils and axis cylinders than in such cerebral areas — not only with the ordinary 

 diffuse stains, but with Bielschowsky's method, which here so frequently stains the 

 glia fibrils — a finding which numerous writers have noted in cerebral areas. In two 

 areas stained by Cajal's method, there were found a very large number of persistent 

 axis cylinders ; in one case (fig. 430) the whole fine reticulum of axis cylinders and 

 their branches were retained, but in three other small areas no axis cylinders could 

 be found. By the diffuse stains, in numerous instances, it could be asserted that 

 almost the whole axis cylinder content of the area was retained. 



(ii) Cerebral area cut in longitudinal direction of the nerve fibres 

 (figs. 370-377). 



Such an area shows no essential changes from those described in the longitudinal 

 direction of a spinal cord area. In my experience the preserved axis cylinders were 

 very much less numerous than in the cord. Fig. 422, taken from an area at the base 

 of a medullary ray, shows the appearance presented in a specimen stained by the 

 Bielschowsky method. 



