966 RADIATION BIOLOGY 



by radiation (Patt et al., 1950, 1952). Its protective action on blood is 

 probably not specific for the hematopoietic tissues but appears rather to 

 be related to an increase in the threshold for radiation effects generally. 

 Enhanced recovery of blood-forming tissue is also apparent when gluta- 

 thione is administered before irradiation (Cronkite et al., 1951). Vita- 

 mins and other nutritional factors have been used experimentally with 

 rather disappointing results (Simmons et at., 1946; Adams and Lawrence, 

 1947; Steamer, 1948; Goldfeder et al., 1948; Cronkite, Tullis, et al, 

 1950; Carter, Busch, and Strang, 1950). Many of these substances are 

 apparently useful in clinical radiation sickness (Shorvon, 1949). Post- 

 irradiation anemia in dogs can be minimized by frequent transfusions of 

 whole blood ; granulocytopenia and thrombocytopenia are not influenced, 

 however, nor is survival (Allen et al., 1951). 



ABNORMAL BLEEDING 



Abnormal bleeding is usually, but not always, associated with the 

 panhematopenia of acute irradiation. The bleeding tendency has been 

 variously attributed to the thrombocytopenia (Shouse et al., 1931; Dun- 

 lap; 1942; Holden et al., 1949; Cronkite, 1950; Rosenthal and Benedek, 

 1950; Penick et al., 1951; Dillard et al., 1951), blood vessel damage 

 (Rekers and Field, 1948; Field and Rekers, 1949a), and the presence of a 

 circulating anticoagulant (Allen and Jacobson, 1947; Allen et al., 1948). 

 It is probable that each of these factors contributes to radiation hemor- 

 rhage, though to a different degree, depending upon species and conditions 

 of irradiation. While hemorrhage is an almost invariable feature of the 

 acute radiation syndrome, the extent and distribution of bleeding may 

 vary considerably among the different species and among animals of the 

 same species. Its severity depends, moreover, upon the completeness of 

 irradiation and the dosage and manner of exposure. 



Purpura and petechiae, though evident in the mouse, rat, and rabbit, 

 are most severe in the dog, man, and probably the guinea pig; bleeding 

 from the body orifices is not uncommon in these species (Allen and 

 Jacobson, 1947; Allen et al., 1948; Rekers and Field, 1948; Field and 

 Rekers, 1949a; Kohn and Robinett, 1948; Rosenthal and Benedek, 1950; 

 Shields Warren and Bowers, 1950). Hemorrhagic manifestations are 

 first seen about a week after irradiation in the median lethal range and 

 reach their peak during the second and third weeks. Extravasation of 

 red cells results in a bloody lymph which becomes manifest several days 

 after exposure and reaches a maximum during the period of greatest 

 bleeding (Bigelow et al., 1951). Bleeding may be widespread but is more 

 often localized in various subcutaneous sites and in the gastrointestinal 

 and urinary tracts, heart, and lungs. In general, the sites most subject 

 to trauma bleed first. The distribution of hemorrhage apparently differs 



