686 



RADIATION BIOLOGY 



Much larger doses were required to damage all spermatocytes and 

 spermatids; and primitive spermatogonia, mature spermatozoa, and the 

 epithelial cells of the testis were found to be even more resistant. 



Differential sensitivity of cells of rodents in various stages of spermato- 

 genesis has been determined by fertility tests and by histological examina- 

 tion of the irradiated testes (see, for example, Snell, 1935, 1941; Snell and 

 Ames, 1939; P. Hertwig, 1938, 1941; Henson, 1942; von Wattenwyl and 

 Joel, 1941, 1944). Histological examination of testes of irradiated mice 

 by P. Hertwig (1938) showed that the sensitivity of the germ cells to 

 radiation decreased with their increasing maturity. The youngest cells 

 disappeared first, and the mature spermatozoa last (Table 9-14). Similar 



Table 9-14. Disappearance and Reappearance of Various Types of Spermato- 

 genous Cells in the Irradiated Testis of the Mouse 



(P. Hertwig, 1938) 



The symbol X indicates the presence of cells after a treatment of 800 r; the symbol * 

 indicates the presence of cells after a treatment of 200 r; the symbol indicates the 

 occasional appearance of the cells in question. Testes in the 200-r series were fixed 

 only 4, 6, 9, 13, and 21 to 46 days after irradiation. 



results were obtained in studies in which mice were irradiated by injection 

 of P 32 in isotonic saline (Warren, MacMillan, and Dixon, 1950). Females 

 inseminated by irradiated spermatozoa often produce abnormally small 

 litters (see, for example, Snell, 1935; Brenneke, 1937), which suggests 

 that the ionizing radiations induce dominant-lethal chromosomal aberra- 

 tions. Among the viable progeny fertility may be reduced. Snell (1935, 

 1941) attributed such semisterility to the presence of chromosomal aber- 

 rations, induced in the paternal gamete (see also P. Hertwig, 1941; 

 Roller and Auerbach, 1941). 



