HISTOPATHOLOGY OF CNS RADIATION 185 



the choroid plexus are about equally affected (Clemente et al., 1960; Hay- 

 maker et al., 1958) . 



Dilatation of the ventricular system has been seen after radiation 

 (Clemente et al, 1960; Demel, 1926), but this is variable from animal to 

 animal. It is greatest in young animals. 



In the pituitaiy, both anterior and posterior lobes are severely damaged in 

 head or whole-body radiation f Haymaker et al, 1958; Mogilnitzky and 

 Podljaschuk, 1928: Vogel et al., 1958). 



Comment 



In spite of numerous disagreements in the results of various workers, a 

 general pattern of degeneration and repair is beginning to be defined in the 

 tissue reactions of the central nervous system to gamma and roentgen radia- 

 tion. It is quite possible that further advances can be made by particular 

 study of points where contradictions in results now exist. 



The series of studies re\iewed ha\e been carried out on widely dixergent 

 species of animals, ranging from goldfish to monkey. It is not certain how 

 many of the contradictory results are dependent on species variation or to 

 what characteristics of indi'.idual species these differences arc related. The 

 demonstration of certain constant features in a wide range of experimental 

 animals suggests that species differences may be more related to details than 

 to the general pattern of response. The high degree of sensitivity of the 

 brainstem in animals far apart in the phylogenetic scale is an instance in 

 point. 



In nearly all experiments re\iewed and in personal material, there are 

 e\en more puzzling variations from animal to animal when radiation source, 

 experimental conditions, and other technical aspects have been kept as 

 constant as possible. Special studies of the animals which are particularly 

 sensitive or resistant in a given set of experimental conditions may suggest 

 factors not well recognized. 



Some such factors may involve the biologic state of the animal at the time 

 of radiation. Rugh ( 1958) has stated, "Probably the most effective physical 

 factors which influence irradiation sensitivity at any biological level are: 

 (a) state of hydration, (b) degree of oxygenation, and (c) amount of 

 activity or movement." The abolition of early cerebellar effects by bar- 

 biturate anesthesia, as demonstrated by Alvord and Brace (1957'i, may be 

 related to such factors. The apparently simple question of what is the 

 minimum dose of radiation which produces damage to the central nervous 

 system is actually one of great complexity. 



