976 ADVENTURES IlSr RADIOISOTOPE RESEARCH 



to a similar extent to that in the tumoui^^*) under the effect of ionizing 

 radiation. Hardin Jones's results^^^) in this field are instructive. He 

 compared the depressing effect of whole-body radiation on blood-cell 

 counts with the reduction in the turnover rate of formation of labelled 

 deoxyribonucleic acid in tumour and liver. Some of his results are seen 

 in Table 7. They show similar figures for percentage depression of blood 

 corpuscles, which is at least partly caused by inhibition of deoxyribo- 

 nucleic acid formation in the bone marrow, and deoxyribonucleic acid 

 formation in the tumour and liver. 



Table 7. — Depkessing Effect of Irradiation with a Dose of 1 r of X-rays 



(Hardin Jones) 



System investigated 



Percentage depression 

 due to irradiation 



White corpuscle count or lymphocyte count 



Red corpuscle count 



Formation of labelled deoxyribonucleic acid in tiunour 

 Formation of labelled deoxyribonucleic acid in liver . . . 



0.23 

 0.3 

 0.18 

 0.28 



INDIRECT RADIATION EFFECTS 



The work of Dale^^^^ and others on the effect of X-rays on enzyme 

 suspensions led to the result that part of the effect of irradiation on 

 enzymes is caused by the production of noxious agents in the solvent. 

 Inactivation of the enzymes is to a large extent caused by the interaction 

 of these noxious agents produced in the water with the enzyme. Dale 

 found that with a given dose inactivation is obtained of a considerably 

 smaller fraction of a concentrated than of a dilute carboxy-peptidase 

 solution. This observation suggests the explanation, and the only feasible 

 one, that the number of inactivating atoms or molecules produced under 

 the effect of w^eak doses of X-rays in the solvent suffices only to inactiv- 

 at3 a restricted number of enzyme particles. The primary process in 

 the action of radiation on water is detachment of an electron and its 

 subsequent transfer from the ion to one of the neighbouring molecules 

 or ions(37). For pure water the primary process is (HO)~H+ -{-radia- 

 tion :^ HO + H. 



Most of these decomposition products have an exceedingly short life 

 and may recombine to form water or react wdth protective molecules 

 present before they reach the enzyme surface. Besides the existence of 



(34) Ahlstrom, Euler and Hevesy, Arkiv Kemi 19, A Nr. 9 (1944). 

 ^^^' Proc. Oberlin College Radiation Biology Meeting, in press. 

 *'3«) Biochem. J. 34, 1367 (1940). 

 ■37) Weiss, Nature 53, 748 (1944). 



