240 



E. Y. GRAYEVSKY, et cd. 



Ivanitskaya, 1956); (b) in a removed spleen (or its portion) left in the 

 abdominal cavity after exposure; (c) in a spleen whose nerve-vessel 

 bundle was clamped after irradiation. Typical necrobiotic processes 

 developed when the ligature was removed (Barakina, 1959b). 



2 4 6 



Time after irradiation (days) 



Fig. 2. — The average number of bone-marrow cells (b.m.c.) per field of vision (as a 



percentage of the normal number) in mice totally X-irradiated with 700 r. 

 1, irradiation only; 2, irradiation + intravenous injection of homologous b.m.c, 

 X-irradiated with 700 r in vitro; 3, irradiation -f intravenous injection of intact homo- 

 logous b.m.c. 



These data suggest that the death of irradiated cells is jirobably due 

 to the loss by the injured, inti*acellular substx'ate of the ability to per- 

 form some function specific to it under normal conditions. If one can 

 create conditions ]5reventing the function of damaged substrate one 

 can succeed in prolonging the life span of the irradiated cells. 



5. The early mass death of haematopoietic cells and those in intesti- 

 nal crypts is not related to mitosis or to chromosome rearrangements. 



About 60 per cent of bone-marrow cells underwent necrosis after 

 X-irradiation of the mouse with 700 r (Barakina, 1957, 1959c, and 

 Eig. 3). Mitotic index in the mouse bone-marrow is equal to 1 per cent, 

 and the duration of the resting stage is 4 to 6 days (Widner et al., 

 1951). Taking into consideration that the exposure to 700 r sharply 



