200 NORBERT SCHUMMELFEDER 



of the damaged brain tissue in the form of numerous gitter cells. Within 

 the preserved tissue only slight glial reaction had occurred. 



Partial Necrosis of Cerebellar Tissue Following Exposure to X-ray 

 Doses from 10,000 to 4,000 r 



At radiation doses from 10,000 r down to 4,000 r, there was necrosis only 

 of the granular layer and a loss of single nerve cells in the other parts of 

 the cerebellar cortex. The latent period between irradiation and the develop- 

 ment of morphologic changes was longer than with higher doses. 



Thus, with a dose of 5,000 to 4,000 r, the first morphologic changes 

 appeared at approximately 12 hours. At this time only a few scattered 

 pyknotic nuclei of granular cells were observed. The other parts of the 

 irradiated cerebellar tissue were not modified. 



At 5 days the more superficial part of the granular layer had undergone 

 partial dissolution. Only adjacent to the Purkinje cell layer was there a 

 zone of preserved pyknotic granule cell nuclei, and it was narrow. Occupy- 

 ing regions in which granule cells had undergone dissolution were numerous 

 gitter cells and i.solated pigment-bearing scavenger cells. Purkinje cells were 

 destroyed only in the most severely damaged regions of the irradiated field. 

 In their place, proliferated glia were seen. Other Purkinje cells were being 

 phagocytized. The cerebellar white matter was loosened strikingly, and in 

 some foci the white matter was completely destroyed. Some of the blood 

 vessels, especially the capillaries, were greatly dilated and were surrounded 

 by a mantle of mononuclear cells including a few neutrophilic leucocytes. 

 Endothelial cells of occasional blood vessels were swollen. 



At 10 days after irradiation the destroyed Purkinje cells were replaced 

 by glial shrubbeiies ( Gliastrauchwerk) extending from the Bergmann layer 

 into the molecular layer. The uppermost part of the molecular layer showed 

 decided shrinkage, as did other parts of the cortex (Fig. 8). 



At 20 days after exposure to 5,000 r, extensive perivascular hen:iorrhages 

 were often found in damaged cerebellar tissue. Shrinkage, pronounced glial 

 proliferation, and cicatrization (gliosis) occurred in the irradiated tissue. 

 The glial fibers within the damaged molecular layer, particularly those of 

 the Bergmann cells, were thickened remarkably. These coarse fibers could 

 easily be demonstrated by Lendrum's (1947) method. 



Persisting Piukinje cells and nerve cells of the inolecular layer often 

 showed regressive changes, e.g., swelling of cytoplasin and nucleus or 

 chromatolysis. Even at this time interval, some of the granule cells in the 

 irradiated area were pyknotic. Such pyknosis had probably developed in 

 the course of the radiation damage. The periphery of the most severely 

 damaged area was marked off by pronounced vascularisation. The vessels 



