1082 RADIATION BIOLOGY 



since whatever the spleen accomplishes under these circumstances must 

 be through the blood stream. That the factor (or factors) must be 

 supplied early is also strongly supported by the fact that, in mice given a 

 lethal dose of radiation, spleen transplants are more effective on the day 

 of irradiation than on the second day after irradiation. In other words, 

 supplying the factor responsible for initiating the functional repair in 

 some unknown minimum number of cells throughout the body must be 

 accomplished early enough to reverse the processes that ordinarily end in 

 death of the animal. Once the factor is adequately supplied, as is 

 clearly demonstrated by the splenectomy experiments, the process of 

 repair is initiated ; yet histologic evidence of repair or regeneration is not 

 apparent for 4 or more days. 



Indirect transfusion initiated on the fourth postirradiation day has 

 been reported to be unsuccessful in significantly increasing survival of 

 X-irradiated dogs (Allen et at., 1952). This apparent failure of whole- 

 blood transfusion to enhance survival and reduce morbidity effectively is 

 understandable if it is assumed that (1) the amount of the factor (or 

 factors) present in the blood per unit volume is small and therefore rela- 

 tively large amounts of blood would be necessary to initiate effectively 

 the recovery process or (2) the factor (or factors) was administered too 

 late and in too small a quantity after exposure of the recipient to initiate 

 the repair process in time and widely enough in cells of the body to have 

 a critical effect on morbidity and survival. The preliminary experiments 

 of Swisher and Furth (1951) indicate that the morbidity of dogs exposed 

 to dosages of X irradiation in the mid-lethal range is reduced if as little 

 as 250 cc of whole blood, collected in ACD solution from a compatible 

 donor, is administered to irradiated dogs shortly after exposure. The 

 ineffectiveness of cell-free extracts obtained from extirpated splenic tissue 

 or embryos may only indicate that too small an amount of the factor is 

 present or too small an amount of the factor is obtained in the extracts 

 from these tissues by present methods. A method of preservation or con- 

 centration of the factor (or factors) or a more sensitive method of assay may 

 be necessary before a positive result can be obtained by cell-free extracts. 

 If the factor is present in whole blood in a concentration sufficient to 

 alter the radiation syndrome even when given in relatively small amounts 

 soon after irradiation of the recipient, then varying the conditions and 

 methods of the administration of whole blood may supply important 

 clues to the identification of the factor (or factors). 



