1064 RADIATION BIOLOGY 



changes in the hematopoietic tissue of the shielded body part if the 

 general toxicity produced by the irradiation is severe. 



"STIMULATION" OF BLOOD-FORMING TISSUE BY RADIATION 



The evidence that small or large doses of penetrating radiation stimu- 

 late blood formation directly is unconvincing (Bloom, 1948). On the 

 other hand, secondary or "compensatory" increases in certain of the 

 cellular constituents of the peripheral blood and in the blood-forming 

 tissue have been observed repeatedly. Such compensatory "stimula- 

 tion " is invariably preceded by a reduction of certain cellular constituents 

 of the peripheral blood and destruction or inhibition of cells within the 

 blood-forming tissue (Bloom, 1948; Jacobson, Marks, and Lorenz, 1949; 

 Murphy, 1926). These findings are based on histologic or hematologic 

 observations and are to be differentiated from chemical or metabolic 

 changes within cells that may occur after irradiation and that might be 

 labeled "stimulation." This is also true when the problem of indirect 

 effects of irradiation is considered. 



MEASURES MODIFYING DESTRUCTIVE EFFECTS OF IRRADIATION 



OR AFFECTING RECOVERY 



Many substances that have been used to treat hematologic disorders in 

 the human being have also been screened for their possible prophylactic 

 or therapeutic value. Simmons et at. (1946) and Jacobson, Steamer, and 

 Simmons (1947) found that, in experimental animals, substances includ- 

 ing folic acid, liver extract, ascorbic acid, and pentnucleotide were of no 

 demonstrable value in reducing radiation injury or in hastening recovery 

 from this injury. 



Only those prophylactic measures that have shown conclusive evidence 

 of effect on the hematologic recovery pattern from radiation injury will be 

 discussed in the following sections. 



PROPHYLACTIC MEASURES 



Induced Hyperplasia of Blood-forming Tissue. Jacobson, Marks, 

 Gaston, Simmons, et al. (1948) reported that the induction of erythro- 

 blastic hyperplasia by a hemolytic agent (phenylhydrazine hydrochloride) 

 or by repeated phlebotomy prior to irradiation prevented or reduced the 

 atrophy of the bone marrow observed in normal adult rabbits after expo- 

 sure to 800 r of total-body X irradiation. As is shown in Figs. 16-4, 

 16-16, and 16-17, phenylhydrazine produced an anemia, a reticulocytosis, 

 and a hyperplastic bone marrow. Although an anemia was produced in 

 normal rabbits which reached a maximum in 14 days, no further anemia 

 occurred in animals with a phenylhydrazine-induced anemia at the time 

 of irradiation, and, as can be noted by examining the reticulocyte values 



