870 



RADIATION BIOLOGY 



1. MORTALITY 



a. Prenatal. Mortality is reported by almost all investigators, at least 

 for the higher dose series. For doses comparable to those which were 

 used during the preimplantation period by investigators whose work 

 spans both periods, prenatal death, however, is of decreased importance 

 (Job et al., 1935; Russell, 1950; Bagg, 1922; Parkes, 1927). Russell 

 (1950) showed that complete interruption of pregnancy, which often 

 follows irradiation during the preimplantation stages, occurs only rarely 

 as a result of later irradiation. This is obvious from the almost 100 per 



Table 13-3. Percentage of Copulations Resulting in Pregnancy in Controls 



and Following Irradiation with Different Doses at Different Stages in 



the Prenatal Development of the Mouse 



Dose, r 





 100 

 200 

 300 

 400 





 200 



Observation 



Term" 

 Term" 

 Term" 

 Term" 

 Term" 



10^, lSy 2 PC" 



ioy 2 , 13^ PC b 



Yield of litters following treatment on postcopulation day 



Mr^i 



5H-8H 



Pregnancy not diagnosable 



Per cent 

 \v. litter 



72.2 

 100 

 69.0 

 0.0 



w-mi 



Pregnancy 

 diagnosable 



No. 9 9 

 treated 



17 



19 



4 



Per cent 

 \v. litter 



94.1 



94.7 



100.0 



"Russell, 1950. 



6 Russell and Russell, 1950a. 



PC = postcopulation. 



cent yield (see Table 13-3) from females treated with 200, 300, or 400 r 

 in stages when pregnancy can already be diagnosed externally (days 9^2 

 and 10^2 usually; days 11^ through 13^2 invariably) and no less appar- 

 ent from comparison with controls of those females irradiated with 

 200 r at a time when it is unknown whether copulation was fertile (days 

 5}^-S}4)- The question of whether there is prenatal death of individuals 

 within litters, as judged by decrease of average litter size at term, is more 

 difficult to answer since, with the necessarily limited numbers available 

 after subdivision into stage and dose groups, standard errors are large. 

 To diminish this difficulty, data accumulated at this laboratory from 

 several morphological investigations, in which litter size was only an 

 incidental result, have been pooled in Table 13-4 to give a total popula- 



