CELL DAMAGE IN THE MAMMALIAN RADIATION SYNDROME 



241 



decreases the rate of cell multiplication it seems evident that only a 

 small number of cells have time to undergo division in 24 hr (the i^eriod 

 when the early death is completed). Some differentiated cells (lympho- 

 cytes) and differentiating ones which had lost the ability to divide 

 (neuroblasts in brain) also underwent destruction after irradiation 

 (Trowell, 1952; Hicks, 1953). 





Fig. 3. — (a) Destruction of bone-marrow cells, X-irradiated with 700 r in vitro and in- 

 jected into the spleen of an intact mouse; (b) absence of destruction of normal bone- 

 marrow cells, injected into the spleen 4 hr after injection. 



Hematoxyline and eosin. x 600. 



Early cell death is probably not the result of some radiation-in- 

 duced chromosome aberrations (or breaks). There are a number of 

 tissues whose cells do not undergo early death despite the fact that most 

 of the irradiated cells have chromosome injuries. Thus the number of 

 cells with anaphase bridges and acentric fragments in mouse cornea 

 is about 90 per cent after exposure to 700 r and 60 per cent in rat liver, 

 after treatment with 500 r of X-rays. Destruction of these cells prior 

 to mitosis does not occur, however, even after irradiation with con- 

 siderably higher doses (Shapiro, 1959; 1960). 



Intensive processes of mitosis and differentiation are peculiar for 

 most cells undergoing early death. In this case mitosis was shown not 

 to bring about early cell death. Possibly it is the differentiation which 

 realizes a latent radiation injury and causes cell destruction. 



6. One of the main radiation effects is an inhibition of mitosis. Radia- 

 tion-induced decrease in mitotic activity is related to nuclear injury. 



This thesis may be proved by : (a) an almost equal delay of the first 



