1006 RADIATION BIOLOGY 



effects of heat and blast and the lack of precise information regarding 

 conditions of exposure. The accident cases, on the other hand, represent 

 uncomplicated radiation injury. 



The disturbance consequent to irradiation assumes a distinctive time 

 course, which depends not only upon the dosage, duration, and manner 

 of irradiation but also upon the temporal relation between injury and 

 recovery of particular cells and their rate of utilization by the organism. 

 The initial damage leads to a complex chain of events, some of which 

 are a direct result of the primary injury while others are secondary to it. 

 Alteration in the cellular constituents of peripheral blood is an example of 

 the former; in fluid balance, of the latter. All the changes are dis- 

 tinguished by their lack of specificity. 



Supralethal irradiation is followed by a shocklike reaction and death 

 within a few days. Severe intestinal damage and central nervous system 

 disturbances are prominent sequelae of massive irradiation. After 

 median lethal irradiation, there is an initially mild disturbance, a brief 

 period of apparent respite, and a final phase of progressive injury with 

 death or recovery. The waves of mortality that occur after moderate 

 irradiation suggest that multiple factors may be involved. These have 

 not been defined satisfactorily. It is apparent, however, that leukopenia, 

 septicemia, hemorrhage, and gastrointestinal damage constitute the most 

 important insults to the irradiated organism. 



Medical management of the radiation syndrome may be resolved into 

 three basic components: (1) correction of the panhematopenia, (2) pre- 

 vention or treatment of infection, and (3) maintenance of adequate nutri- 

 tion and fluid balance. Although irreversible tissue injuries occur soon 

 after intensive irradiation, there are indications that it may be possible to 

 prevent effectively certain of the radiation changes and to facilitate the 

 regenerative capacity of critical tissues. It is noteworthy, for example, 

 that morbidity and mortality are influenced by procedures that promote 

 recovery of blood-forming tissues or prevent bacteremia, e.g., spleen and 

 marrow transplants, and antibiotics. Data pertaining to biological pro- 

 tection against the acute syndrome by means of organ shielding are most 

 impressive and should encourage further attempts to influence tissue 

 recovery with humoral agents (cf. Chap. 16). From a practical point of 

 view, it is imperative to establish the role of blood transfusion, hemato- 

 poietic and antihemorrhagic factors, and parenteral feeding. Early 

 venesection and blood replacement have been shown to reduce radiation 

 mortality in dogs; periodic blood transfusions, on the other hand, mini- 

 mize anemia but apparently do not influence other radiation sequelae or 

 mortality. 



Specific chemical protection against many of the effects of ionizing 

 radiation is of considerable theoretical importance. Elucidation of these 

 protective mechanisms may reveal the nature of the early chemical 



