350 ANDERSSON, LARSSON, LEKSELL, MAIR, REXED AND SOURANDER 





Fig. 3. Myelin preparation showing extensive necrosis and multiple perivascular 

 hemorrhages 4 days after irradiation with a 10 mm high energy proton beam. Dose: 

 20 krad. Hcidcnhain. X 9. The photographs are published by courtesy of Acta 

 Radiologica. 



Transverse Lesion of the Cerebral Hemispheres 



Twenty rabbits were irradiated with a 1 .5 mm broad beam directed trans- 

 versely through the upper part of the frontal lobes. The dose was 20 krad. 

 The rabbits remained functionally unaffected during the time they were 

 allowed to survive, up to about 1 year. Macroscopic changes consisted of a 

 red or green groove on the anterosuperior surface of the brain, and in some 

 instances, on the medial surfaces of the hemispheres as well. No large hemor- 

 rhage was seen, and the leptomeningeal vessels in the groove were not throm- 

 bosed. Sagittal sections of the brain showed a well demarcated lesion in the 

 cortex, white matter, and caudate nucleus, which up to 3 months after irra- 

 diation was approximately restricted to the path of the beam. After 

 3 months the lesion was slightly broader than the beam (Fig. 4). 



