1116 » RADIATION BIOLOGY 



four doses, dead spermatogonia are seen; 24 hours after nine doses, 

 spermatogonia are rare and there is a marked decrease in spermatocytes ; 

 after 14, 20, 24, and 35 daily doses of 80 r, there is a gradual elimination of 

 spermatogenesis until only the Sertoli cells remain. 



In the testis of guinea pigs exposed daily to 8.8 r of y rays from a 

 radium source, there is early destruction of some spermatogonia while 

 others develop into spermatocytes and eventually into spermia. With 

 continued irradiation, no regeneration of spermatogonia occurs and the 

 damage is progressive. After 37 daily treatments (326 r) spermatogenesis 

 is absent (Heller, 1948b). After 46 exposures (405 r) and 81 exposures 

 (713 r), only Sertoli cells remain and nearly all cellular debris has been 

 removed from the lumens of the tubules. From 37 days on, large 

 vesicular cells resembling fibroblasts are prominent around the tubules 

 and among the interstitial cells. However, after 81 exposures the 

 epididymis still contains spermia. 



Histologically, the findings are the same in mice similarly treated, but 

 complete cessation of spermatogenesis is less rapid. Although there is 

 considerable generalized degeneration after two months of irradiation 

 (8.8 r per 8-hour day), practically complete depletion of the tubules 

 (except for Sertoli cells) is not observed until the eight-month interval 

 (Eschenbrenner, 1946; Spargo et at., 1951). In mice irradiated with 4.4 r 

 per day, the testis shows only slight degenerative changes up to 10 

 months. Twelve to 16 months of treatment cause slight but progres- 

 sively increasing degeneration. Irradiation at the rate of 1.1 r per day 

 produces no visible changes in the testis up to 16 months. 



Exposure of rabbits and mice to fast neutrons in comparable fractions 

 of the LD 50 30-day level results in similar but even more severe damage 

 to the testis than X irradiation (Heller, 1948b; Lawrence and Tennant, 

 1937). In addition to these degenerative and regenerative changes in 

 the tubules, the interstitial connective tissue in the mouse contains focal- 

 ized masses of plasma cells and some areas of hematopoiesis. There is 

 also some inflammation in the epididymis. The testes of young rabbits 

 show the peak of damage at 21 days, when every tubule contains a dense 

 amorphous material and an occasional huge basophil cell. In the sur- 

 rounding connective tissue there is frequently considerable extravascular 

 and intravascular erythropoiesis. 



Beta rays from an external P 32 source produce extensive damage at 

 the periphery of the testis near the source of the radiation. The damage 

 decreases toward the interior of the organ. In the least damaged por- 

 tions regeneration is rapid, but the outside margin is incompletely 

 recovered 28 days after exposure to 2500 rep. Besides the dead cells in 

 the severely injured marginal tubules, giant and bizarre cells are often 

 prominent (Heller, 1948b). 



Although the effects of internally administered radioactive isotopes are 



