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Fio. 1. Mouse thymus, (a) Lymphocyte 34 minutes after whole-body X-irradiation with 

 600 r — N, nucleus with slight derangement (patchy condensation) of the chromatin pattern; 

 C, clear zone in cytoplasm; | , centriole; M, mitochondria. X 20,000. 



(b) Thymic medulla, 1 hour after whole-body X-irradiation with 600 r — | , perinucleolar 

 halo. Various discrete stages of nuclear chromatin derangement and margination. X 5,000. 



(b) 



