400 JANSSEN ET AL. 



had long- processes which extended up to the lower edge of the band. Sub- 

 sequently, the astroglial reaction was present in the subcortical white matter 

 and corpus callosum, particularly in the region adjacent to the interhemi- 

 spheric fissure (Fig. IIC). In later stages after irradiation (up to 5 months), 

 the zone of tissue destruction became increasingly narrowed and was de- 

 void of astrocytic elements; however, along the upper and lower surfaces of 

 the zone hypertrophic astrocytes persisted. 



Oligodendroglia in both cerebellum and cerebrum were diflficult to im- 

 pregnate. Data on their vulnerability are, thus, not available. 



Reactive changes of microglia in the cerebellum and cerebrum in Hortega- 

 Penfield preparations were first noted at 48 hours after irradiation. In the 

 cerebellum at this time there were scattered reactive microgliacytes in the 

 cortex. Subsecjuently, they were noted over a wide irradiated area (Fig. 12A) . 

 A similar microglial response was observed in the cerebral cortex, being 

 particularly evident in the white matter beneath the mesial cortex, i.e., in 

 the region adjacent to the interhemispheric fissure. At earlier stages hyper- 

 trophied microglia were noted here and there at various levels of the cortex. 

 With the development of a band of nerve cell damage, microglia appeared 

 within the band as well as in the underlying cortex and white matter. 

 Changes in the cerebral cortex at the 4 day stage are illustrated in Fig. 12B. 

 Subsecjuently, most of the microglia were in a hypertrophic state and occa- 

 sionally appeared ameboid. Gitter cell forms were few. After the first week 

 following irradiation, the zone usually contained microglial cells which, 

 when their cell body was round, could be distinguished from oligodendro- 

 cytes by the short thorny spikes on their main cytoplasmic processes (Fig. 

 12C). In adjacent areas, most conspicuously just above the band, diffusely 

 scattered hypertrophic cells, including rod cells, were noted. 



Mesenchymal elements 



In general, both histiocytic and fibroblastic reactions occurred in the 



Fig. 11. Alpha particle radiation, 6,000 rad surface dose. Cajal preparations of 

 cerebrum. ^. (5 days) In the band (the clear region in the middle of the photograph), 

 there are occasional necrotic nerve cells and astroglia. In the part of the zone about 

 the band, nerve cells have vanished or are in a necrobiotic state ; astrocytes, which are 

 hypertrophic, are disintegrating. Beneath the band the astrocytes are hypertrophic 

 and have prominent processes oriented toward the band. X335. B. Astrocytes in the 

 corresponding area of a normal control rat. X400. C. (16 days) A fairly wide band 

 extends across the cortex. In the middle of the photograph some nerve cells beneath 

 the band are damaged, and hypertrophied astroglia are to be noted from the level 

 just beneath the band down to, and including, the corpus callosum, where an area of 

 the white matter is pallid. Vascular dilatation is most prominent in the region of the 

 zone and the band just above the area of damage beneath the band. X44. 



