CELL DAMAGE IN THE MAMMALIAN RADIATION SYNDROME 



239 



and iiialignaiit human and animal (;ells when irradiated lost their 

 ability to foi-ni macrocolonies aiter explantation and died, ])rol)ably, 

 because of chromosomal aberrations. The \A),i^ for these cells ranged 

 from 50 r to 150 r. 



Fig. 1. — Mouse bone-marrow 6 hr after total-body X-irradiation with 700 r. (a) shielded 



portion ; (b) irradiated portion. 

 Hematoxylin and eosin. x 400. 



Most mouse bone-marrow cells are known to undergo destruction 

 after total-body irradiation with 700 r. At the same time a susijension 

 of these cells in vitro did not undergo desti'nction when exposed to 

 700 to 1000 r. However, such cells lost their ability to restore haema- 

 topoiesis after injection into lethally-irradiated mice (Fig. 2) which 

 may probably be explained by the death of these cells in the host 

 organism. x\.s a matter of fact cells irradiated iii vitro and injected 

 directly into the spleen of a normal monse soon nnderwent destruction 

 (Barakina, 1959b). McCulloch and Till (1960) injected lethally irra- 

 diated mice with isologous bone-marrow cells X-irradiated in vitro or 

 in vivo with various doses. They fonncl that the LD37 for these cells 

 was 105 rad. The LD37 for monse leukemia cells is equal to 160 r of 

 y-rays of 6OC0 (Hewitt and Wilson, 1959). 



4. Cell destruction after irradiation does not take place in artifi- 

 cially isolated parts of the haematopoietic system. 



No destruction of cells was observed: (a) in portions of spleen ex- 

 planted in tissue culture or incubated iri vitro after exposure and also 

 in an irradiated suspension of bone-maiTow cells (Barakina, 1959b; 



