D. W. VAN BEKKUM 



the spleen after a dose of 50r, some cell debris is clearly recognizable in most 

 of the lymph follicles, while in an occasional one very little if any sign of 

 damage is to be found. After lOOr, a greater number of nuclear fragments 



c6 



"o 



E 



^60 



■50 



-30 

 20 - 

 10 



I 



Jl 







C 



Figure 2. Oxidative phosphorylation of rat spleen mitochondria at 4 hours after 



various doses of total body irradiation. Black bars : phosphate uptake in 



(jimol/mgN ; white bars : oxygen uptake in [xatoms/mgN 



and pycnotic nuclei have been observed, but the damage is markedly less 

 than after the larger doses of radiation. 



In thymus slices only a small amount of nuclear fragmentation could be 

 observed at 4 hours after 50 r and mitotic figures were still present. After 



^60 



"a so 



"I liO 



ri- 

 30 



20 



10 





__ 



1 



n 



C i- c ^ c ^ 



Ci O Q> 



cs Ci C> 



^ Co ^ 



m 



C f- c 



1 



u 



(7 f- C f- 



Figure 3. Oxidative phosplwrylation of rat thymus mitochondria at 4 hours after 



various doses of total body irradiation. Black bars : phosphate uptake in 



[xmol/mgN ; white bars : oxygen uptake in [xatoms/mgN. 



lOOr the signs of destruction were more extensive, although many apparently 

 normal nuclei and a few mitotic figures remained. Although no accurate 

 estimation of the amount of visible damage has been attempted, it appears 

 that the minimal doses of total body irradiation required to produce morpho- 

 logical evidence of nuclear damage in a sizable number of cells and those 



203 



