216 



L. F. LAMERTON 



in these bleeding experiments between normal and irradiated animals was the 

 lack of a marked leukocytosis in the irradiated animals, suggesting that the 

 leucocyte stores in the body had been considerably reduced. 



At the moment it is not possible to say whether the megakaryocyte- 

 platelet and white cell systems differ with respect to the dose-rates that can be 

 tolerated. At the higher dose-rates of 415, 176 and 84 rads/day the low platelet 



Controls 



o 

 o 



20 

 16 

 12 



8 

 A 

 



A 

 



28 

 24 



20 



16 



12 



8 



4 

 



Haemoglobin 



Platelets 



Polymorphs 



Rats irradiated continuously 



at 50 rads/day 

 for 130 days before bleeding 



4 8 12 16 20 4 8 12 16 20 



Days after bleeding Days after bleeding 



Fig. 3. Response of rat to removal of one-third blood volume by cardiac puncture. Cora 

 parison between normal rats and rats irradiated for 130 days at 50 rads per day. 



count appears to be the major cause of death (leading to a rapid haemorrhage) 

 but at the same time the monoculear and polymorphonuclear counts are also 

 very low. 



Studies of cell proliferation in the bone-marrow, using tritiated thymidine 

 as a label for dividing cells, have given some indication, at 50 and 84 rads/ 

 day, that the mean proliferation rate is increased for both red and white cell 

 precursors (Lord, unpublished). More detailed studies of generation time are 

 at present under way, but one would suspect, from various Imes of evidence, 



