228 Barbara E. Holmes 



sense that mitoses occur at 27-28 hours after the hepatectomy. 

 These are fewer than in the control and show many chromo- 

 some breaks and the DNA synthesis rate is lower. It is 

 plain that this question of the irradiation of the resting liver 

 tissue should be further investigated. 



It is worth mentioning that Dr. Koller, who carried out 

 cytological investigations on squashes of the irradiated liver 

 material, found a very high chromosome breakage rate 

 (percentage numbers in Fig. 1) in the belated mitoses after 

 irradiation at 12 hours after hepatectomy. This early stage 

 is not usually supposed to be a sensitive stage as regards the 

 production of chromosome breaks. (All the mitotic counts 

 were done by Dr. D. Cater.) 



In much of the work on regenerating liver, described in the 

 literature, whole body irradiation is used. For our experiments, 

 irradiation was given immediately over the area of the right 

 hand liver lobe and the rest of the abdomen was screened with 

 lead rubber. In early experiments we removed food from the 

 cages and gave both control and irradiated animals injections 

 of glucose saline. More recently we have found that the 

 irradiated animals will eat quite well and we have not taken 

 any such special steps. Animals showing any adverse symp- 

 toms, or lack of muscular tone, or which have lost an unusual 

 amount of blood at operation or have subsequently injured 

 the muscle scar by struggling, cannot be used. These conditions 

 cause delay in regeneration. 



In experiments with regenerating rat liver, as with Jensen 

 rat sarcoma, it is found that irradiation inhibits the ^^P 

 uptake into DNA but not into RNA. Ord and Stocken (1956) 

 agree with this, but point out that in some tissues RNA 

 synthesis is also affected. Abrams (1951) found some inhibit- 

 tion of 22P uptake into the RNA fraction of some mouse 

 tissues after whole body irradiation. In normal as well as 

 regenerating liver Kelly (1952) has found that whole body 

 irradiation will cause a depression of ^^P uptake into nuclear 

 RNA but an increase in cytoplasmic RNA. 



Kelly and Payne (1953) also studied the effect of whole 



