336 A. J. S. DAVIES, ANNE M. CROSS, AND P. C. ROLLER 



cases injection of bone-marrow hastened recovery towards normal. It is also 

 apparent that as early as 10 days after irradiation, if bone-marrow were given, 

 the level of recovery was almost independent of the radiation dose. It should 

 however, be remarked that the number of cells given was high in relation to 

 the number reqiured to ensure survival (see Table II) and therefore the number 

 of cells available was unlikely to have been a factor luniting speed of recovery. 



Table II. The survival at 30 days of BALBjC mice given first 700 r, total-body, 

 then within 24 hours various numbers of isogenic bone-marrow cells 



Table II records an example of experiments in which the number of cells 

 injected after irradiation was varied. There were at least 30 mice in each group. 



Table III. The peripheral blood values {as percentages of control) of BALBjC 



mice that had 10 daijs previously received 700 r, total-body, followed closely by 



various numbers of isogenic bone-marrow cells intraveneously 



It appears that survival is more or less independent of the number of cells 

 injected between 10* and 10^ but if 10' cells are given survival can be 100 %• 

 A possible explanation for this finding can be adduced from the data in Table 

 III in which the effects, upon the peripheral blood values, of varying the 



