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MALIS, ROSE, KRUGER AND BAKER 



produce a restricted lesion deep in the cortex with a single irradiation, since 

 one can take advantage of a sharp increase in the number of ionizations pro- 

 duced for a short distance near the end of the beam path, just before all 

 ionizations drop abruptly to zero as the particles are stopped by the tissue 

 (Malis t'^ al., 1957, 1958). 



Figure 1 illustrates a typical laminar lesion 65 days after irradiation with 

 20 Mev deuterons. The laminar lesion is a sharply demarcated strip com- 

 pletely free of nerve cells. There is a noticeable loss of nerve cells in cortical 

 layer IV just above the laminar lesion; the still more superficial cortical lay- 

 ers (II and III) and the cortical zonal lamina (layer I) appear substantially 

 intact. 



A laminar lesion covers an area commensurate with the aperture used. Its 

 dorsoventral dimensions are always limited, though the width of the lesion is 

 a function of the radiation dose. With smallest effective doses, the width of 



Fig. 1. Laminar lesion (1) in the striate (St) and peristriate (Ps) areas of a rabbit. 

 The extreme edge of the lesion just extends into the posterior limbic region (PI). 

 Due to the scatter of the beam, the lesion is narrower in the peristriate than in the 

 striate field. 65 days after irradiation. Peak dose: 33,000 rads; average dose: 12,000 

 rads; surface dose: 7,000 rads; number of deuterons per cm": 8.8 X 10" I=lst 

 cortical layer, II — IV=cellular cortical layers. X 30. 



