1062 RADIATION BIOLOGY 



In general, the number of morphologic abnormalities observed are 

 directly proportionate to the radiation dosage sustained by the blood- 

 forming tissue. There is little evidence that cells are injured in the 

 peripheral blood (Furth et al., 1951). The injury that results in the 

 observed abnormalities in the peripheral blood is undoubtedly sustained 

 or produced by the irradiation effects on the various maturation stages of 

 the precursors in the blood-forming tissues. With doses in the LD 50 

 range or above, an anemia was invariably produced in all the species of 

 laboratory animals that have been investigated. In the presence of an 

 anemia, anisocytosis, poikilocytosis, macrocytosis, microcytosis, and 

 polychromasia were found. The degree of these red-cell abnormalities 

 depends, in general, on the type and chronicity of the anemia. 



Nucleated erythrocytes were observed soon after exposure but reached 

 a maximum between the tenth and twenty-fifth day after irradiation. 

 This represents the period of maximum anemia in the peripheral 

 blood and the stage of maximum regeneration of erythropoiesis in the 

 marrow. 



Degenerative morphologic changes in the platelets were found by 

 Jacobson, Marks, and Lorenz (1949) in the peripheral blood of animals 

 following median lethal doses and above of roentgen radiation. Giant 

 platelets were frequently seen concomitant with reduction in platelet 

 values. Except for increased size and distinctive granular degeneration, 

 no further morphologic alterations were found in the platelets of the 

 peripheral blood. Only on rare occasions were megakaryocytes found in 

 the peripheral blood after total-body roentgen irradiation in the LD 50 

 range. 



The morphologic changes in the lymphocytes of the peripheral blood 

 increased with increasing amounts of radiation. Clumping of nuclear 

 chromatin was seen early. Histologic studies indicate that this change, 

 which occurred with relatively small doses (~50 r), may actually be 

 reversible in some lymphocytes (Jacobson, Marks, and Lorenz, 1949). 

 As it became more pronounced, pale bluish opaque areas were encount- 

 ered. In addition, lymphocytes were seen with rounded chromatin 

 masses seemingly free within the nuclear membrane. At the time of 

 maximum lymphocyte reduction in the peripheral blood after irradiation, 

 mononuclear cells with a somewhat basophilic cytoplasm and with 

 nucleoli were often prominent. These latter cells are indistinguishable 

 from "blast" forms. Occasionally mitotic blast cells appeared after 

 semilethal or higher doses. Other lymphocytes appeared to have split 

 nuclei and nuclei with considerable fragmentation. With the LD 5 o range 

 of acute total-body irradiation, these destructive changes were more pro- 

 nounced. Remnants of nuclear fragments, without nuclear outline and 

 which could not be distinguished as belonging to either the myeloid or 

 lymphoid series, appeared. Many lymphocytes were bilobed, whereas 



