968 RADIATION BIOLOGY 



workers who fail to find consistent changes in the coagulability of whole 

 blood in a number of species, although the clotting time of plasma may 

 be increased and clot retraction diminished (Kohn and Robinett, 1948; 

 Kohn et al, 1948; Dixon, 1948; Holden et al, 1949; Cronkite, 1950; 

 Rosenthal and Benedek, 1950; Cohn, 1951). Cronkite (1950) believes 

 that the bleeding tendency and the coagulation defect when observed can 

 be attributed primarily to the severe thrombocytopenia and associated 

 phenomena. Whole hemophilic blood with normal platelet levels has 

 been found to accelerate the clotting of irradiated dog blood (Penick et al., 

 1951). This is not the case with platelet-poor hemophilic plasma. 

 Platelet transfusions have been shown to reverse the coagulation defect 

 and to prevent bleeding in an irradiated dog (Dillard et al., 1951). 

 Multiple transfusions of whole blood are ineffectual, however (Allen 

 et al., 1951). We cannot account for the lack of agreement regarding the 

 etiology of radiation hemorrhage, i.e., thrombocytopenia vs. heparin-like 

 substances. Some of the seemingly discordant observations may be 

 attributed to differences in experimental techniques, e.g., in the with- 

 drawal of blood and the determination of the various components of the 

 clotting mechanism, or in the species of animal and dosage of radiation. 

 Recent evidence indicates that thrombocytopenia is the chief factor in 

 the pathogenesis of abnormal bleeding. 



There is some evidence that alteration in vascular fragility also plays a 

 role in the hemorrhagic syndrome. This is largely indirect, however. 

 Petechiae may be induced more readily in irradiated than in nonirradi- 

 ated animals and bleeding is generally most severe at the points of great- 

 est trauma (Field and Rekers, 1949a; Allen et al., 1948). Bleeding cannot 

 always be related to thrombocytopenia and the delayed clotting reaction 

 (Field and Rekers, 1949a). Reference has already been made to the 

 flooding of lymph by erythrocytes, indicative perhaps of capillary damage 

 (Bigelow et al., 1951). Rutin, a flavonol glucoside that is considered by 

 some investigators to influence vascular fragility, has been shown to 

 hasten recovery of the skin of rats after local irradiation (Griffith et al., 

 1947) and to minimize hemorrhage and improve the survival of dogs after 

 total-body irradiation (Rekers and Field, 1948; Field and Rekers, 1949a). 

 To be effective, rutin must be given for a week or so before or preferably 

 both before and after irradiation. Since reduction of hemorrhage occurs 

 with rutin despite depression of the blood platelets and prolongation of 

 clotting, it has been proposed (Field and Rekers, 1949a) that rutin either 

 decreases the rate of vascular disintegration or increases its repair. It is 

 not known whether hyaluronidase plays a role in altered capillary fra- 

 gility. Hyaluronidase inhibitors have been tried in a few irradiated dogs 

 without success (Field and Rekers, 1949b). Bleeding is said to be dimin- 

 ished in guinea pigs that are fed a diet supplemented with cabbage, 

 possibly because of its high content of vitamins P and C (Lourau and 



