PHYSIOLOGY OF RADIATION INJURY 965 



not fibrinogen. Since the sedimentation rate in dogs may be increased by 

 as little as 100 r to the whole animal, it is doubtful that this is a simple 

 reflection of bacterial invasion. 



In general, the sensitivity of blood and blood-forming tissues increases 

 from rabbits to rats, mice, and chicks and then to men, goats, guinea pigs, 

 and dogs (Jacobson, Marks and Lorenz, 1949). Since this is roughly the 

 order of increasing sensitivity to the acute lethal action of X rays, rather 

 comparable blood changes appear in each species after a median lethal 

 exposure. Differences in recovery exist, however; after comparable 

 hematologic injury recovery is more rapid in the rat than in the rabbit. 

 There are also indications that the acute lethal dose for a species may be 

 related to the sensitivity of its heterophils. Similar lymphopenias have 

 been observed in the rabbit and guinea pig following irradiation with 

 200 r (Brues and Rietz, 1948). The heterophils, on the other hand, are 

 decreased markedly only in the guinea pig with this dosage. Comparable 

 heterophil depression is not observed in the rabbit until its lethal range is 

 approached. That there may be some correlation between the heterophil 

 response and acute lethality is also indicated by the rapid recovery of 

 heterophils, but not of lymphocytes, in mice treated with estrogens prior 

 to irradiation (Patt, Straube, et al, 1949). 



While consistent hematological differences between survivors and 

 decedents are not always apparent, the clinical signs of acute intoxication 

 generally parallel the hematological findings (Rekers, 1949; Ingram and 

 Mason, 1950). It does not necessarily follow that death is due to blood 

 damage, but the fact that morbidity and mortality can be influenced 

 appreciably by procedures that presumably promote recovery of the 

 blood-forming tissues suggests that such damage is a substantial factor 

 in the radiation syndrome. 



A number of agents have been employed in an attempt to modify the 

 hematological response to radiation. Reference has already been made 

 to the effectiveness of spleen shielding (Jacobson, Marks, Robson, et al, 

 1949), spleen transplants and homogenates (Jacobson, Simmons, Marks, 

 and Eldredge, 1951; Cole et al, 1952), and bone marrow injections 

 (Lorenz et al, 1951, 1952). Increased resistance of erythropoietic tissues 

 has been noted following the production of a regenerative anemia by 

 phlebotomy, phenylhydrazine, and exposure to high altitude (Jacobson, 

 Marks, Gaston, Simmons, and Block, 1948; Schack and MacDuffee, 

 1949). It is of interest that hyperplastic erythroid tissue shows less 

 injury than normal tissue. Pretreatment with estrogens has been shown 

 to induce a rapid recovery from radiation granulocytopenia and to 

 minimize anemia in mice (Patt, Straube, et al, 1949). The estrogen 

 effect may be related to stimulation of activity, in this instance, of the 

 myeloid tissues, following an initial depression. Cysteine is an effective 

 prophylactic against the hematological changes induced in rats and mice 



