EFFECTS OF WHOLE-BODY IRRADIATION 255 



sensitivity of erythrocyte synthesis (perhaps aided by reflection and strong 

 absorptions of X rays within the long bones; and (2) the rather subtle, and 

 perhaps more serious, sensitivity of the central nervous system itself. In the 

 first case, changes in blood count have been measured. In the second, the 

 appearance of new and changed peaks in the electroencephalogram have 

 been observed. The meanings of these peaks in terms of effects on memory, 

 judgement, irritability, etc., are only vaguely understood so far. 



Accumulation of all this information — effects on both human beings and 

 animals — has provided rough rules-of-thumb which are very useful. One 

 can be sure, however, that they are by no means final. For instance, it is 

 known from studies of persons connected with radiation therapy in hospi- 

 tals that doses of less than 1 rem/wk produce definite symptoms of irradia- 

 tion damage over several years. Yet a complete diagnostic X-ray examina- 

 tion of thorax and intestines, even when done under the responsibility of a 

 very competent radiologist, delivers about 1 rem to the tissues being studied. 

 Since long-term genetic effects are indicated by what information is avail- 

 able, and since the genetic results really are not yet known for humans, 

 maximum permissable dose and dose rate have been arbitrarily chosen for 

 radiologists, patients, and workers with ionizing radiations in industry and 

 government. For X and gamma radiation, the current value is 0.3 rem/wk 

 (or 0.3 rem individually to the blood-forming organs, to the gonads, to the 

 lens of the eye, to other organs and tissues), and it may soon be revised 

 downward. If the rate is 0.02 rem/hr the work is considered very hazardous. 

 However, these tolerances, as well as the minimum shielding requirements, 

 are now very carefully controlled by the governments of most countries, and 

 the symptoms and necessary precautions are continuously being revised and 

 published as new information bearing on these questions accumulates. 

 However, background irradiation from rocks, cosmic rays, tritium in the 

 water, etc., amounts to 0.15 to 0.4 r/yr, and because of long-term genetic 

 effects which may result from even small doses to humans, physicians, es- 

 pecially, should be aware of the potential harm of needless and incompetent 

 clinical exposure to diagnostic X rays, and aware of the possible effects 

 which may result from an ever-increasing background. In these terms the 

 probable effects of all-out or even limited nuclear war are distasteful to dis- 

 cuss. One could mention especially those effects from radioactive gases 

 which could enter the lungs; and those from dust-carried "fallout" contain- 

 ing such isotopes as Sr 90 which can enter the bones and teeth, and, having a 

 low turnover rate there and being a hard beta-emitter (0.54 and 2.26 Mevs) 

 with a long half-life (25 yrs), could irradiate the human body continuously 

 from within — and nothing could be done about it, except to try to chelate it 

 out by some chemical process .... However, one can provide for himself 

 some protection (see Fig. 9-9). 



