POSTIRRADIATION TREATMENT OF MiCE AND RaTS 141 



mental animal and the dog is the animal of election. Moreover 

 the results of Brecher and Cronkite can equally well be attri- 

 buted to the transfer of some factor in solution or colloidal 

 suspension in the plasma exchanged. Such a substance could 

 "detoxify" the damaged animal — an hypothesis which did 

 not appeal to the authors — or act as a stimulant for that 

 early regeneration of the recipient's bone marrow which was 

 observed. This histological finding by itself suggests that the 

 effect was more than that expected from the symptomatic 

 treatment of continuous transfusion with whole blood. Still 

 another suggested alternative was the possibility of a transfer 

 of blood-forming cells from the donor. 



Another surgical procedure has been much more widely 

 investigated. Jacobson and his colleagues (1949) first showed 

 that irradiation of mice with their spleens protected was much 

 less lethal than complete irradiation of the whole body plus 

 spleen. They proceeded to demonstrate (1951) that, in similar 

 fashion, a reduced mortality of the totally irradiated mouse 

 could be attained by implanting intraperitoneally spleens 

 from normal mice, accelerated regeneration of the haemo- 

 poietic tissues being identified as the fundamental effect of 

 this procedure. Similar, dramatic changes in mortality were 

 reported by Lorenz and his colleagues (1951, 1952) following 

 the injection of suspensions of bone marrow into irradiated 

 mice. Jacobson (1952), in a comprehensive review of the work 

 of his group and of Lorenz and colleagues, marshalled the 

 evidence in favour of his hypothesis that a humoral factor in 

 normal spleen and bone marrow (both haemopoietic tissues in 

 the mouse) was responsible for stimulating the recovery of 

 the irradiated animal's damaged haemopoiesis. Only one argu- 

 ment seemed to the present authors to be incontestably in 

 favour of this hypothesis, namely that heterologous material 

 from guinea pigs had, in the hands of Lorenz and colleagues 

 (1952), been effective. The principle was confirmed later by 

 Congdon and Lorenz (1954) who obtained positive results 

 using bone marrow from rats. 



Further evidence in favour of the humoral hypothesis 



