362 



MALIS, ROSE, KRUGER AND BAKER 



Fig. 3. Section adjacent to that shown in figure 2. Schultze's silver stain for fibers. 

 Laminar lesion (1) is filled with nerve fibers which form a dense striation and inter- 

 rupt the orderly radial arrangment of the fiber bundles. Notice the near normal appear- 

 ance of the remaining portion of the cortical field. X 60. 



pared with a \ariety of histologic techniques i from brains of animals surviv- 

 ing from several days to 18 months after irradiation, we concluded that many 

 nerve fibers in the laminar lesion must be new sprouts. 



We have reported on the technique as well as on the histologic appear- 

 ance of the laminar lesions and the problem of fiber growth in considerable 

 detail elsewhere (Malis ct al., 1960; Rose ct al., 1960). However, consider- 

 ing the interest in the problem of the radiation dose, we will repeat a few 

 points concerning the technique as well as some problems arising in regard to 

 the determination of the dose. 



All irradiations were carried out with the beam from the 60 in. cyclotron 

 at Brookhaven National Laboratory, which delivers 20 Mev deuterons, 10 

 Mev protons, or 40 Mev alpha particles. Irradiations were done mostly with 

 the deuteron beam, because its range in the brain (about 2.5 mm) is twice 

 as large as the ranges of available protons or alpha particles. Figure 5 illus- 

 trates the irradiation arrangement. The evacuated beam pipe brings the col- 



