2 A. Haddow 



words, the passage of radiation through hving tissues obviously 

 initiates a long chain of events. We have the primary ioniza- 

 tions, the chemical consequences, and the biological events 

 which follow. Although the physical nature of the primary 

 actions has been well worked out, and the chemical con- 

 sequences have been established, at least in numerous simple 

 cases, the link between the chemical changes and the biological 

 consequences is almost completely unknown. Discussing the 

 radical initiated polymerizations of unsaturated substances, 

 Butler points out that the radical merely acts as a catalytic 

 agent in that it stimulates processes which can occur spon- 

 taneously. This recalls a recent impression that the chemical 

 carcinogens may simply expedite processes which occur 

 spontaneously at much lower rates. Again to quote Butler, 

 we are at the moment in the position of a man who tries to 

 elucidate the mechanism of a telephone exchange by throwing 

 bricks into it and observing some of the results. 



Our subject is at an elementary stage, yet it is always 

 dangerous to say what will not happen in science. Even 

 Lord Rutherford at one time thought little of the prospects 

 of the release of atomic energy. From the study of the influence 

 of ionizing radiations on cell metabolism may, however, flow 

 the most profound consequences for the theory of ageing, for 

 the theory of carcinogenesis, and for the theory of heredity. 

 J. J. Thomson once said that if he were to start life again he 

 would take up the study of biology, this being, as he thought, 

 at the same stage as physics when he started his early career. 

 Our own subject is the ideal region in which physics, chemistry 

 and biology meet. 



