354 SPECULATIONS ON CELLULAR ACTIONS 



the chemical standpoint a cell is about as impure a system as one is 

 likely to encounter. Accordingly the suspected process must be iden- 

 tified in the living cell. This is usually a difficult task, but with advances 

 in biochemistry, particularly in analyses of intact cells, we ma^^ expect 

 more information of this sort. 



Unfortunately, even if a suspected process can be demonstrated to 

 occur in the irradiated cell, this is far from adequate to establish its 

 relevance. As we have seen, it seems highly probable that most of the 

 processes initiated by irradiation are irrelevant to any single end effect, 

 although they may be relevant to other effects. Accordingly, the radio- 

 biological process suspected of relevance must be connected (3) by some 

 means with other processes and states, especially the observed end effect. 

 Since, as just noted above, we are in practice largely limited to indirect 

 methods, it appears that the modifiers of dose-effect relations are likely 

 to be our chief means of establishing connection. For instance, if we 

 were studying inhibition of cell division and found that peroxide w^as 

 formed in the irradiated cells before division was affected, and if further 

 it was found that each of the various modifying factors affected peroxide 

 formation and inhibition of cell division in essentially the same manner, 

 we could be reasonably justified in concluding that peroxide formation 

 was relevant to the action on cell division. 



In my foregoing remarks I have pointed out certain types of informa- 

 tion needed for an understanding of radiobiological mechanisms and 

 some of the general methods which might be employed to obtain such 

 information. However, I have not said much about methods at the 

 laboratory level. There is much room for advance here, as is obvious if 

 we cast a thoughtful glance at Figs. 1 and 2. 



In the first place, we have at present only a fragmentary knowledge 

 of the normal state of the cell. This situation wall improve as general 

 cellular biology improves. As radiobiologists we have an enormous stake 

 in the advance of general biology. 



About energy transfer (process A) we can infer quite a lot from ob- 

 servations on gaseous systems, but much valuable information is still 

 lacking, such as (a) the average energy required to activate a molecule 

 in the cell; (6) the relative numbers of ions and excited molecules pro- 

 duced; (c) the detailed distribution of individual energy transfers in the 

 ionization track; {d) the lifetimes of the initially activated molecules; 

 (e) the possible ways in which energy may be transferred from the 

 initially activated molecules to other molecules. 



At the other end of the story there is even more room for improve- 

 ment. Many of the end effects which we observe and try to measure are 

 probably the results of compHcated mechanisms involving relatively 



