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



Fig. 1. Longitudinal section of rabbit's spinal rord; myelin jjicparation showing 

 localized damage 12 days after irradiation with a 1.5 mm beam of high energy pro- 

 tons. Dose: 20 krad. Heidenhain. X 9. The photographs are published by courtesy of 

 Acta RadioJoQica. 



stain was always negative. The occurrence of a small number of well pre- 

 served axons and myelin sheaths in the subpial region of the irradiated part 

 of the cord was remarkable and constant. 



To study the relationship between the breadth of the beam and the type 

 of radiation damage, a group of animals was irradiated with a beam 10 mm 

 broad, the dose being the same as in the first series. Three to 4 days after 

 irradiation, rapidly progressing paresis developed in the hind legs. These 

 animals were killed 1 to 6 days after irradiation. Macroscopically, hyperemia 

 of the meninges and spinal cord corresponding to the path of the beam was 

 seen 1 to 3 days after irradiation, and numerous petechial bleedings 3 to 6 

 days after irradiation. The earliest histologic changes foimd, at 1 and 2 days 

 after irradiation, consisted of dilated capillaries and veins containing large 



