12 PHYSICAL PROCESSES IN LIVING MATTER 



domain, the actual energy transfer from radiation to tissue matter is 

 not simple in nature. The discussion of such a complex physicochemical 

 system in detail is beyond us; add the evident subtlety of the biological 

 problem, and you will see why facile all-embracing explanations find little 

 favor with physicists. But it is equally clear that the construction of 

 models, like the very important and general target model, and the 

 elaboration of such models both in concept and by experimental changes, 

 are the only means of progress. By the steady growth and test of our 

 oversimple ideas we will weed out of the whole picture those features 

 which are decisive in each of the many problems which interest the radio- 

 biologist. We know already the importance of energy density for many 

 processes; we know the importance of diffusing products for others. It 

 is the hope of the physics panel, as the other essayists continue to fill in 

 the details of the physical picture I have sketched, that from this snap- 

 shot of the events within an atomic collection workers in the other fields 

 will be able to create a colorful and penetrating set of artistic and 

 convincing portraits. 



REFERENCES 



1. See, for example, the discussion of N. Bohr in the monograph on stopping prob- 

 lems, Kgl. Danske Videnskab. Selskab, Mat.-fys. Medd., 18: 8, 1948. 



2. The standard treatment is that due to H. A. Bethe, Handbuch der Physik, vol. 

 24/1, pp. 491 ff., Berlin, 1933. 



3. Compare H. A. Bethe, Revs. Modem Phys., 22: 213, 1950, and 9: 261, 1937. 



4. Bohr, A., Kgl. Danske Videnskab. Selskab, Mat.-fys. Mcdd., 24: 19, 1948. 

 Halpern, O., and H. Hall, Phys. Rev., 73: 477, 1948. 



5. Gray, L. H., Brit. J. Radiol., Supplement 1, p. 7, 1947. 



6. Lea, D. E., Actions of Radiations on Living Cells, Cambridge, 1946. 



7. Jaffe, G., Ann. Physik, xlii: 303, 1913. Read, J., Brit. J. Radiol, 23: 504, 1950. 



8. See the discussion and paper by R. Platzman, p. 158 in this volume. 



