870 ADVEXTUKKS IN RADIOISOTOPE RESEARCH 



arrest can explain a decrease of not more than 5 per cent in the course 

 of three days (Soberman, Keating and Maxwell, 1951). If the addi- 

 tional decrease is due to haemolysis produced by irradiation or to leakage 

 through the capillary wall cannot be stated. 



By making use of radioiron as an indicator, extended studies were 

 carried out by Lamerton and his colleagues (cf. Baxter et al., 1955) 

 on the pattern of recovery from radiation damage and how this is in- 

 fluenced by shielding procedures. They demonstrated infer alia that 

 anaemia observed in animals given 450 r with one hind limb shielded 

 is less severe than in animals given the same dose of whole body radiation; 

 the bone marrow of the shielded limb shows a high degree of erythro- 

 poietic activity two to three days after irradiation. The spleen of a 

 shielded animal becomes actively erythropoietic much earlier than in 

 an unshielded animal. The hind-limb shielding is almost as effective in 

 lessening the severity of the anaemia in the splenectomized as in the 

 intact animal. 



GROWTH PROMOTION 



Determination of biochemical reaction rates with great accuracy may 

 reveal that every such reaction is influenced in some way by exposure 

 to radiation. In numerous cases which time prevents me from discussing 

 even in part, such influences were ascertained. The great radiation sen- 

 sitivity of the DNA molecule and its formation, the far-reaching con- 

 sequences of the radiation damage produced by such an interference, 

 and the important role radioactive indicators played in revealing the 

 depression of DNA formation under the effect of exposure to radiation 

 induced me to discuss this type of radiation damage more in detail. 



By making use of radiophosphorus as a tracer it could also be demon- 

 strated that growth going on in one organ may promote DNA formation 

 in other organs. Kelly, Lola, Payne, White and Jones (1951) investi- 

 gated the incorporation of ^^P into DNA of the organs of mice bearing 

 bilateral transplants of mammary carcinoma (cf. also Cerecedy, Lom- 

 BARDi, Reddy and Travers, 1952; Smellie, McIndre and Logan, 

 1953). As can be seen in Fig. 13, incorporation of ^^p into DNA of the 

 liver of the mouse, and thus DNA formation in that organ, is promoted 

 b)y the presence of mammary carcinoma, ^^P incorporation increasing 

 with the age of the tumour transplant, ^^p incorporation into DNA was 

 also found to be promoted in the spleen and kidney but not in the 

 intestinal mucosa of mice with mammary carcinomas. 



Kelley and Jones (1953) found furthermore that DNA turnover 

 can be increased in livers and spleens of normal mice by repeated injec- 

 tions of various fractions of homologous tissue mashes and also of cell- 

 free extracts of such mashes. 



