380 D. C. VAN DYKE, P. JANSSEN AND C. A. TOBIAS 



provide evidence as to the mechanism involved in the acquisition of stain- 

 abihty of brain tissue following" irradiation. 



It should be emphasized that the results presented in this paper both for 

 fluorescein staining' and morphologic changes represent acute changes follow- 

 ing high doses of irradiation and are for the most part confined to observa- 

 tions during a 3 week postirradiation period. The possibility of profound 

 changes occurring in the central nervous system many months or years after 

 relatively low doses of irradiation has been adequately emphasized by other 

 studies (Arnold ct ai, 1954c; Lindgren, 1958) and has not been considered 

 in this work. 



The doses of alpha particle irradiation which must be given in order to 

 produce changes in the central nervous system have been found to be rela- 

 tively high (above 5,000 rad ) . Parallel studies done by Janssen et al. (1961) 

 using alpha particle irradiation confirm the finding that a dose in excess of 

 5,000 rad (6,000 was the minimum effective dose found by these authors) 

 must be given before morphologic changes are observed at any postirradia- 

 tion inteival in the rat. However, Hicks and Montgomery (1952) have shown 

 that 6 to 24 hours after x-ray doses of as little as 1,200 rad to the head of 

 rats, necrotic oligodendroglia cells were found scattered through the white 

 and gray matter. 



The greater radiosensitivity of the primate brain as compared to that of 

 the rodent brain which was found in this study both by the fluorescein 

 staining technique and gross or microscopic morphologic examination, has 

 been observed and emphasized by Arnold ct al. ( 1954a,b,c) and by Lindgren 

 (1958) . The work of these authors indicates that the greater radiosensitivity 

 of the primate brain occurs not only in the early postirradiation period after 

 high doses, as was the case in this study, but also after long postirradiation 

 periods and relatively low doses. Lindgren (1958) has emphasized that the 

 radiosensitivity of the brain appears to vary from one region to another, 

 cortex and the medullary region immediately underneath it being less radio- 

 sensitive than deep-seated parts of the white matter ( Markiewicz, 1935; 

 Pennybacker and Russell, 1948; Zeman, 1950). The radiosensitivity of the 

 white matter also appears to vary from region to region, as is suggested by 

 the disseminated appearance of the lesions on uniform irradiation of the 

 entire brain (Scholz and Hsu, 1938) and by lesions seen in the midbrain 

 (Arnold vt ai, 1954b). One must be cautious in generalizing about brain 

 tissue as a whole, and cautious in comparing work done with diflferent types 

 of radiation, different species, and different postirradiation intervals, until 

 more data have accumulated. 



Monkeys given 11,000 rad showed a response greater than that loimd in 

 rats after 26,000 rad, suggesting that at this dose the brain tissue of the 

 monkey is almost 3 times more radiosensitive than the brain tissue of the 



