POSTIRRADIATION TREATMENT OF MiCE AND RaTS 143 



compatible with its being cellular. To test this further 

 we have adopted one of the schedules recommended for 

 the preservation of living cells (Smith, 1954), i.e. storage 

 of the material in glycerol at — 79° C, and found that 

 the activity is preserved for 80 odd days at least (Barnes 

 and Loutit, 1955). 



(5) The activity is destroyed by a dose of a few hundred 

 rontgens of X-rays in vitro (Cole et al., 1953) and in 

 vivo (Barnes and Loutit, 1954) which again is more in 

 favour of its being of a cellular rather than a chemical 

 nature. 



(6) In most laboratories it is not possible to keep the sur- 

 vivors of animal experiments for the rest of their lives. 

 We have had sufficient accommodation to allow us 

 to do so. We have thus accumulated information on 

 the overall survival of the normal unirradiated CBA 

 mice of our colony (these are not strictly controls in 

 the temporal sense), and mice irradiated with 950 r 

 and treated with isologous (CBA) spleen, spleen from 

 homologous strain A mice and heterologous bone 

 marrow from Wistar rats. The median survival time 

 of the unirradiated mice is 900 days. For the irradiated 

 animals only those which survive the conventional 

 30 days are included for scoring. Routinely they 

 come to experiment at about the age of 100 days. The 

 median survival time for those given isologous spleen 

 is a further 400 days and for those given homologous 

 spleen approximately 40 days. From the Hmited data 

 for heterologous transfer, the survival seems much the 

 same as for homologous. 



(7) The previous result suggests .that antigenic differences, 

 such as occur between cells of various origin, are im- 

 portant. We have another similar observation in that 

 CBA animals, previously immunized by intravenous 

 injections of tissues from mice of strain A, will no 

 longer recover following irradiation with 950 r if treated 

 with spleen from strain A (Barnes and Loutit, 1954). 



