1078 



RADIATION BIOLOGY 



tion (Jacobson, Simmons, Marks, and Eldredge, 1951) it was reported 

 that, if splenectomy was performed within 10 minutes after the irradia- 

 tion-spleen-shielding procedure, none survived. Further work, how- 

 ever, has shown that leaving the spleen in the circulation for as little as 5 

 minutes is sufficient to significantly increase the survival of mice exposed 

 to 1025 r (Jacobson, Simmons, Marks, Gaston, et al., 1951). Full 

 recovery of the blood-forming tissues is delayed longer in mice splenecto- 

 mized 5 minutes after irradiation than in mice splenectomized 24 hours 



6 9 12 15 19 22 



TIME AFTER X RAY, days 



29 



• • CONTROLS 



o -o SPLENECTOMY CONTROLS 



o » 1025 r WITH LEAD SHIELDING 



o o 1025 r WITH LEAD SHIELDING; SPLENECTOMY 



WITHIN 5 MINUTES AFTER X IRRADIATION 

 s s 1025 r WITH LEAD SHIELDING; SPLENECTOMY 



24 HOURS AFTER X IRRADIATION 



Fig. 16-22. Effect of splenectomy on the reticulocyte values of mice exposed to 1025 r 

 of total-body roentgen irradiation with lead shielding of the exteriorized spleen. 



after irradiation (Fig. 16-22). If the originally shielded spleen (whether 

 or not the pedicle is clamped during the irradiation) is not removed, com- 

 plete regeneration of hematopoietic tissue occurs earlier than in mice with 

 splenectomy 24 hours after the shielding procedure (Jacobson, Marks, 

 et al., 1951). These facts indicate that the intact spleen may release 

 enough of the factor in a few moments to enhance significantly the sur- 

 vival but that, if left in the circulation longer, an earlier and more com- 

 plete regeneration of hematopoietic tissue occurs. 



Total-body Exposure to 1025 r plus 200-r Increments to Spleen. Mice 

 have been exposed to 1025 r of total-body X irradiation, and the spleen 

 has been given various increments of the total-body dose. Doses up to 

 and including 200 r may be given to the spleen at the same time as 1025 r 



