FUNCTIONAL CHANGES INDUCED BY RADIATIONS 491 



higher level such as required in extreme emergency (e.g., sustained heavy 

 hemorrhage) . In the same way, we can think of the adaptiveness of kidney, 

 Hver, intestinal, epithelium, pituitary, testes, or skin, with performance 

 function at the normal level or at one of the extremes. Failure does not 

 always result in death. Failure of the testes, for example, results in sterility; 

 failure of the skin, in an open lesion or ulcer. 



Components of the nervous system and the system as a whole can manifest 

 different degrees of performance capability. As in other ecoentities, we 

 have impressions of what is meant by superior mental abilities, by "normal" 

 mental function, and by mental failure. We are aware that a certain level 

 of performance efficiency must be maintained for the nervous system to 

 provide for the usual needs of the organism and that the nervous system, 

 like other systems, has a reserve of capability which can be drawn upon 

 when requirements are excessive. In dealing with the influence of radiation, 

 attention must be given to the entire range of adaptiveness, if considerations 

 are to be at all comprehensive. There is, thus, a range of "wellness" or 

 reserve fitness, as well as a range of "sickness" or deficient fitness, separated 

 by a line designating the level at which there is no clinical evidence of 

 disease or abnormality. 



Determination of normalcy or satisfactory performance in the usual range 

 of freedom from disease is not in itself sufficient reason for saying that a 

 biologic system has not been affected by an agent such as radiation. Reserve 

 capacities must also be considered, if any analysis is to have full meaning. 

 This has particular significance in connection with the nervous system as an 

 information processing device. 



Effects on the Nervous System as a Whole 



Figure 2 shows a range of radiation dosages we wish to consider in relation 

 to treatment of the nervous system with penetrating radiations such as x-rays 

 or gamma rays. Each number is different from the one above or below by 

 a factor of 10. The digit 2 is used because it applies most satisfactorily, 

 especially at the extremes. 



Doses of 200,000 r applied to the head or the whole body of laboratory 

 animals usually result in spastic seizures and death in a matter of minutes. 

 Such killing has sometimes been called nervous system death, inasmuch as 

 death resulting from other kinds of irradiation damage requires a signifi- 

 cantly longer time. In relation to other systems, 200,00 r will interfere with 

 muscular performance, stop sperm motility, and cause measurable bio- 

 chemical changes. 



Doses of 20,000 r will cause rapid loss of motor coordination and seizures 

 of different kinds, leading to death in a matter of hours. The effects appear 



