390 JANSSEN ET AL. 



Fig. 4. Alpha particle radiation, 1,5UU rad surface dose; sacrifice at 216 days. 



A. Cerebral cortex, illustrating a faint nerve-cell-poor band (arrows) extending later- 

 ally from the region of interhemispheric fissure. The meninges appear unaffected. X65. 



B. Lamina in the region of the interhemispheric fissure. Numerous nerve cells have 

 disappeared and others are faded. Two nuclei, presumably those of nerve cells, are 

 enormously enlarged. X410. Van Gieson-hcmatoxylin stain. 



plotted against the Brago curve, coincided with the energy given ofT along 

 the slopes and at the peatc of the curve (Fig. 6) if the assumption could be 

 made that the cerebellum had undergone linear shrinkage by a factor of 

 35% as the result of processing. Measurements were made to test this as- 

 sumption. The maximal width of the cerebellum in the stained section in 

 which the pyknotic cells were counted was 7,590 ju,; when this figure was in- 

 creased by 35%, the value was 11,660 /x. In a control rat of the same age as 

 the experimental animal, the maximal width of a fresh cerebellum immedi- 

 ately after autopsy was 10,120 fx. Thus, the assumption was approximately 

 correct. As to the cerebrum, its width on the stained section was 7,084 /a, 

 and in the imfixed fresh brain, 8,602 ix. Thus, linear tissue shrinkage was 

 relatively less for the cerebrum than the cerebellum. 



Alterations in Structural Elements with Respect to 

 Time-Dose Relationships 

 Nerve cells 



At surface doses of 50, 250, and 750 rad, observations up to 216 days 

 (Table I) failed to re\eal any neiuonal changes. The lowest surface dose at 

 which alterations were seen was 1,500 rad, and then not until the 216 day 

 stage. In the cerebral cortex at this stage, a faint, narrow nerve-cell-poor 

 band was detected (Fig. 4A) . Adjacent to the interhemispheric fissure, the 



