240 C. P. SwANSON AND Bengt Kihlman 



later extension by Giles and his co-workers (reviewed by 

 Giles, 1954) which demonstrated the central role which 

 oxygen plays in governing the degree of chromosomal damage. 

 The radiochemical aspects of radiation and their relation to 

 chromosomal studies have been adequately treated elsewhere, 

 and it needs only to be recalled that the effects of radiation on 

 biological systems can be modified by a variety of experi- 

 mental conditions such that the chromosomal damage may be 

 amplified or diminished. Any initial complacency generated 

 by the knowledge of radiochemical events was of short dura- 

 tion, however, and it is now evident that the radiochemical 

 events are but a link which, in the living cell, connect the 

 physical events of radiation with the observable effects such 

 as aberrations. Latarjet and Gray (1954) have expressed 

 this in the following way: 



I II III IV 



Absorption Primary Chemical Observable 



of radiant — > radiochemical — > reaction — > lesions 

 energy reactions chains 



Step III constitutes the greatest unknown in the above 

 chain of events, and is the one on which our attention will be 

 largely focused. The inadequacy of the first two steps to 

 account for all of the parameters encountered in chromosomal 

 studies with ionizing radiations has been made evident by a 

 variety of observations: among others, the fact that oxygen 

 alone is capable of inducing aberrations (Conger and Fair- 

 child, 1952), the discovery of diff'erential rates of breakage and 

 rejoinability during the course of cell division (Sparrow and 

 Maldawer, 1950; Deschner and Sparrow, 1955) and the role 

 of metabolic inhibitors in modifying the final frequency of 

 aberrations (King, Schneiderman, and Sax, 1952; Wolff and 

 Luippold, 1955). These latter studies strongly suggest the 

 involvement of oxidative metabolism in the ultimate extent 

 and expression of radiation damage. 



Although the radiobiological experiments may make "good 



