242 



E. Y. GRAYEVSKY, et ol. 



cleavage after exposure of gametes (Henshaw and Frances, 1936; 

 Shapiro et al. 1960); (b) the absence of delay after irradiation of the 

 anucleate half of the sea urchin egg and an inhibition of division after 

 the exposure of the nucleated portion of the egg (Henshaw, 1938); 

 (c) the absence of delay in the cleavage of the eggs [Misgurnus fossilis 

 L.) X-irradiated during cleavage or at the early blastula stage when 

 divisions proceed independently of nuclear structure preservation 

 (Shapiro and Lander, 1960a; Shapiro et al., 1960); (d) the absence of 

 mitotic delay after irradiation at the middle l)lastula stage of the eggs 

 if the nuclei were preliminarily strongly impaired by radiation. Ex- 

 posure of normal embryos at this stage always induced temporary- or 

 constant (depending on the dose of radiation) delay of division (Shapiro 

 etal, 1960; Shapiro and Lander, 1960b). 



2 5 



Time after irradiation (days) 



Fig. 4. — xiie average number of bone-marrow cells (b.ni.e.) per field of vision (as a ^jer- 



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

 1, iiTadiation only; 2, irradiation + intravenous injection of isologous b.m.c; 3, irra- 

 diation + intraperitoneal injection of isologous b.m.c. ; 4, irradiation + intravenous 

 injection of heterologous b.m.c; 5, irradiation + intraperitoneal injection of hetero- 

 logous b.m.c. 



7. Destruction and changes of mitotic activity developing as a 

 result of irradiation are not directly connected with changes in the 

 content of nucleic acid derivatives. 



The content of nucleotides and micleosides in the nuclei of mouse 

 bone-marrow cells was shown to decrease markedly in the very first 



