266 



H. HAGER, W. HIRSCHBERGER AND A. BREIT 





.k \\n- Ak 





.gbM 



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Fig. 6. Cerebral cortex, 45 hr after exposure to 15,000 r. Tangential section through 

 a small vein. The perivascular space (PVS), bordered by glial (GBM) and vascular 

 (VBM) basement membranes, is filled with exudate and also contains a monocyte 

 (Mo). Ex, exudate within partially necrotic tissue; Er, diapedetic erythrocytes; As, 

 astrocytic processes containing densely osmiophilic inclusions. X 4,500. 



though polymorphonuclear leucocytes have been literally caught in the act 

 of passing through the vascular basement membrane. This process has been 

 discussed elsewhere (Nelson et al., 1960), but we are still ignorant of the 

 factors that prevent or permit such cellular movement. Plasma exudate is 

 also seen outside the confines of the perivascular space, but it is difficult to 

 determine whether this is in the intercellular space, as are the erythrocytes, 

 or if it is partly intercellular in these incompletely necrotic tissue. A rather 

 common finding is the occurrence of densely osmiophilic inclusions in astro- 

 cytic cytoplasm. Figure 7 shows exudate associated with more definite early 

 necrosis, with dissociation of the normal, intricately arranged components of 

 the neuropil and a disruption of some of their membranes. Nerve cells, such 



