404 JANSSEN ET AL. 



Between 9 and 16 days, there were more filling gaps in the vascular tree in 

 the irradiated zone (Fig. 13B), more evident degenerative changes in the 

 walls of smaller vessels, fibrinoid necrosis and swelling in the walls of occa- 

 sional arterioles in the band, and fusiform and saccular microaneurysms. 

 During these stages the hemorrhages increased in number and size and had 

 a linear arrangement in the band of cerebellar and cerebral damage. Hemor- 

 rhages were occasionally seen below the band. After 18 days, they were 

 rare. In the brains of 2 animals which survived 30 days, the capillary net- 

 work in the band was as rich as in the adjacent cortical tissue. Vessels just 

 above and just below the band were still dilated. At 4 and 5 months, at a 

 time when the band was greatly shrunken, the same vascular conditions 

 prevailed. 



Vascular Permeability to Fluorescein-Labeled Serum Proteins 

 (FLSP) AND Sodium Fluorescein 



Altogether 54 rats (38 for FLSP and 16 for sodium fluorescein studies) 

 were exposed to a 6,000 rad surface dose of alpha particles. FLSP is innoc- 

 uous and imder normal conditions does not penetrate vessel walls. In the 

 cerebellum, penetration of vessels by FLSP was first noted at 72 hours in 1 

 of 3 animals studied. The disturbance of vascular permeability was striking 

 in that intrafolial white matter below the Bragg peak zone showed extensive 

 green fluorescent mottling. In the granular layer within the irradiated zone 

 and below the zone, widespread glial cells contained FLSP inclusions, and 

 in the molecular layer at corresponding levels small FLSP globules were 

 foimd about a few capillaries. The final stage at which increased permeation 

 of FLSP was visible in the cerebellum was in an animal sacrificed 18 days 

 after irradiation. 



In the cerebrum the first microscopically detectable vascular penetration 

 by FLSP was at 48 hours and consisted of small, bright-green fluorescent 

 droplets of FLSP along the outer surface of a few capillaries in widely 

 scattered areas of the exposed cerebral cortex (Fig. 14). At 72 hours the 

 capillaries exhibiting increased permeability to FLSP were much more nu- 

 merous in the cortex, and many neuroglial cells in the imderlying white matter 

 were studded with FLSP inclusions. One cerebrum showed an irregular 

 green fluorescence throughout the imderlying white matter. Subsequently, 

 intraparenchymal FLSP was conspicuous aroimd the blood vessels in the 

 cortex, especially those in the zone. In the underlying white matter, protein 

 inclusions were found in the glial cells, and in some regions the white matter 

 exhibited irregular, mottled FLSP fluorescence. FLSP transport occurred to- 

 ward the pial and ependymal smfaces, as judged by the collection in these 

 regions of protein inclusions. In the cerebrum of 1 of 2 rats sacrified at 36 



