558 WERNER K. NOELL 



the destruction of visual cell life. These two efTects of x-radiation on the 

 visual cell probably have no more in common than that both are the 

 consequence of the basic action of x-radiation, in the physical sense. It 

 would appear, however, that the simple ERG technique used for detection 

 of the photoexcitatory effect (Figs. 13 and 14) might provide a sensitive 

 tool for the evaluation of interactions of x-radiation and biologic matter. 



Conclusion 



The outstanding result of these studies is the close association of visual 

 cell death from x-irradiation with the effects on the sensory function of this 

 cell and on energy-yielding metabolic activities. With the exception of the 

 photoexcitatory action of x-rays, all effects required about the same critical 

 dose. They all seemed to develop at about the same time, as if the whole 

 cell in all aspects of its function suddenly failed. It thus would appear that 

 x-irradiation affects a critical region of the cell, a region on which all the 

 measured activities intimately depend. 



The visual cell characteristically comprises several distinct compartments, 

 each probably having its own distinct function. If this critical region of 

 x-ray action were the nuclear region, then the fact that the ERG disappeared 

 within a few minutes (its main components disappearing simultaneously) 

 would be difficult to understand, since it is well established that the a-wave 

 is closely related to the integrity of function of the outer segment, and not 

 so much to that of the more proximal parts of the visual cell. 



On the other hand, were the outer segment the essential site of the action 

 of x-irradiation, a close association of the ERG effect with cell death would 

 be improbable because destruction of the outer segment is compatible with 

 visual cell survival. 



The only region of the visual cell which intimately might support all 

 other parts of the cell and their functions is the distal portion of the inner 

 segment to which the mitochondria of the cell are confined. The difficulty 

 in assuming that this is the "critical" region derives from the well supported 

 finding that poisons which affect the respiratory chain, and anoxia, have 

 notably little capacity to produce visual cell death. The visual cells of the 

 rabbit, for instance, survive ocular ischemia lasting 75 minutes. 



In view of these difficulties in defining a "critical" region, it seems more 

 probable that x-irradiation affects a dynamic system which is essential 

 everywhere in the cell and which structurally may be represented by the 

 plasma membrane or cytomembranes. In any case, I believe that whatever 

 the system or cell component which x-irradiation affects in the visual cell, 

 a similar or the same system must be an important site of action of x-irradi- 

 ation throughout the nervous system. 



