402 JANSSEN ET AL. 



meninges and in the sheaths of larger vessels in the meninges and in the 

 cerebellar and cortical substance; the histiocytic phase occurred earlier and 

 the higher the dose, the more pronounced it was; the reactions were usually 

 most advanced in the region corresponding to the Bragg peak, and in time 

 they advanced upward in accordance with the irradiation dose. After a con- 

 siderable latent period following exposure to the 3.000 and 6.000 rad sur- 

 face doses, blood vessel walls frequently underwent fibrohyaline change or 

 hyalinosis (Fig. 2C). 



Circulatory and Vascular Changes as Brought Out by Stains 



Sections from 83 brains exposed to alpha particles and from 30 exposed 

 to protons, all at the 6,000 rad surface dose level, were stained by the Pick- 

 worth-Lepehne method from 1 hour to 5 months after irradiation. 



In sections prepared by routine methods, no vascular changes, hemor- 

 rhages, or plasma transudates were encountered in brains exposed to surface 

 doses of 50, 250, 750, 1,500, or 3,000 rad. At 6,000 rad surface dose, the 

 v^arious circulatory and vascular changes produced by alpha particle and 

 proton irradiation were the same, whether in the vessels of the cerebellum 

 or cerebrum. At various times through 18 hours, no vascular dilatation was 

 observed within the region presumably irradiated. It was noted in a rather 

 wide zone of irradiation in both cerebellum and cerebrum at 24, 36, and 

 42 hours. 



In Pickworth-Lepehne preparations, the earliest dilatation of vessels ob- 

 .served in the cerebellum and cerebrum was at 48 hours. It was diffuse in 

 the irradiated region from the pia downward. By 2.5 days, it had become 

 concentrated in the region corresponding to the upper slopes and the peak 

 of the Bragg curve. The lower border of the zone of vascular dilatation was 

 fairly sharp and corresponded to the lower border of the zone of tissue 

 damage, as seen in Van Gieson-hematoxylin preparations. At 3 days, the 

 cerebellum and cerebrum in 1 of 3 rats contained tiny hemorrhages predom- 

 inantly in the "'Bragg peak" area. At 4 days, capillaries within the band had a 

 suggestively swollen basal membrane, while others had collapsed. Within the 



Fig. 12. Radiation, 6,000 rad surface dose. Hortega-Penfield preparations. A. (30 

 days) Proton radiation. Cerebellum. The maximal depth of irradiation is at the level 

 of the highest Purkinje cell. Microgliosis has occurred in the granular layer, intrafolial 

 white matter, and the molecular layer, and Bergmann cells are hypertrophic. XI 10. 

 B. (4 days) Alpha particle radiation. Cerebral cortex. The light area at the top of 

 the photograph is the band of damage. Beneath it are increased numbers of hyper- 

 trophic microgliocytes. X310. C. (30 days) Proton radiation. Region of interhemi- 

 spheric fissure of cerebral cortex, showing a fairly wide band of damage in which 

 great numbers of microgliocytes are congregated. X 145. 



