1034 



RADIATION BIOLOGY 



comparable. Although individual animals in all these species may have 

 a reduction in the circulating heterophils after exposure to 100 r, a 

 significant reduction in well- controlled experiments occurs only after 

 exposure to 200 r or more. The relatively great sensitivity of the blood- 

 forming tissue of the guinea pig, cat, and dog, however, is reflected in a 

 significant heterophil reduction even after exposure to dosages of 200 r 

 or less. Aubertin and Beaujard (1908) reported an initial rise in the 

 polymorphs following exposure to dosages in the LD 50 range, with a 

 return to about normal in 24 hours and a maximum depression by 2-4 

 days. This was confirmed by Jacobson et al. (1947), who showed, in 

 addition, that actually two separate elevations occur in the rabbit in the 



12,000 



12 16 20 24 28 32 

 TIME AFTER EXPOSURE, hours 

 -* CONTROLS o o iQOr a * 500 r 



36 40 



Fig. 16-2. Effect of single doses of total-bod y roentgen irradiation on the heterophil 

 values of the peripheral blood of rabbits. 



first 24 hours after exposure (Fig. 16-2). A heterophil rise in the first 24 

 hours is characteristic of all species studied, but this rise may be entirely 

 masked in species in which lymphocytes constitute the larger percentage 

 of the circulating leukocytes. That the initial rise in granulocytes is 

 followed by a reduction after exposure of rabbits to dosages of 500 r or 

 greater is shown in Fig. 16-3. Recovery is usually complete in 12-21 

 days even with dosages of 800 r. An "abortive rise" in the heterophil 

 value is characteristically seen after dosages of 500-800 r. This tem- 

 porary elevation appears between the fourth and eleventh day. A similar 

 elevation is observed in lymphocyte values during the same postirradia- 

 tion period (Fig. 16-1). 



The mechanism of the leukocytosis within the first 24 hours after 

 exposure is not well understood. Isaacs (1934) and Wuensche (1938) 

 described a hastening of maturation of granulocyte precursors in the bone 

 marrow and have suggested that the release of these cells into the circula- 



