NEW EVIDENCE ON THE MECHANISM OF RADIATION LEUKAEMOGENESIS 



45 



Regarding the "bone-marrow effect" in radiation leukaemogenesis, one 

 experiment, involving injections of isologous bone-marrow following urethane 

 treatment, after an initial total-body radiation, has already been described. 

 A further experiment is in progress, in which the action of urethane is being 

 tested in relation to partial-body radiation. From as yet incomplete results, it 

 would appear that urethane can produce at least a partial "reversal" of the 

 inhibition of shielding. 



Table III. Influence of hone-marrow injections on X-ray leukaemogenesis in 

 C57BL/6 mice, with and without urethane treatment 



Group 



Primary 

 treatment"!" 



Secondary 

 treatment"!" 



No. of 



mice 



used 



Leukaemia 

 incidence 



Leukaemia incidence, 

 excluding generalized 

 nonthymic leukaemia 



"!" Irradiation: single total-body exposure to 400 r. Urethane: 0-2 ml of 10% solution 

 (20 mg) injected intraperitoneally and repeated ten times at weekly intervals (totalling 200 mg). 

 A suspension of isologous bone-marrow, injected intravenously once only in groups 4 and 5 

 (20-24 hr after irradiation), and repeated ten times in group 2 (24 hours after each urethane 

 injection). Interval between irradiation and first vu-ethane injection was 2 weeks. 



Another experiment, designed to investigate the role of the thymus in 

 relation to the two-stage system, showed that the inhibition resulting from 

 thymectomy could not be reversed by subsequent urethane treatment. 

 Further work is in progress, to determine the phase in the two-stage process 

 at which re-implantation of normal thymus becomes effective in reversing the 

 inhibition caused by the initial thymectomy. It is still too early to report on the 

 finduigs of this experiment. 



The most interesting series of experiments to be reported, however, are 

 those designed to investigate the possible role of a virus in radiation leukaemo- 

 genesis. 



The relevant data from previous work are (i) the demonstration by Gross 

 (1951, 1958) of a viral agent in leukaemic tissue of high-leukaemia strains of 

 mice, that is capable of transmitting the disease to newborn mice of a low- 

 leukaemia strain; (ii) the subsequent observation by Gross (1959) that such 

 an agent can also be demonstrated in leukaemic tissue of a low-leukaemic 



