878 RADIATION BIOLOGY 



ninth and eleventh days with 35-50 r yielded 160.6 males per 100 females 

 (i.e., 61.6 per cent males) without modifying the litter size. Control 

 ratios are not reported and even significance of the difference from a 1 : 1 

 ratio cannot be calculated since the actual numbers for this group are not 

 given. (In other groups, similar with respect to stages irradiated, the 

 sex ratio appears normal; e.g., treatment between the eighth and eleventh 

 days with 27-90 r gave 141 males and 132 females.) It may, however, 

 be pointed out that a 1 : 1 sex ratio is not necessarily expected at birth 

 even if it exists at conception. Russell (1950) reports 61.0 per cent new- 

 born males in one group of controls (difference from 50 per cent males = 

 2.5 X S.E.) in comparison with which the excesses of males in both 

 broad experimental categories (preimplantation and postimplantation) 

 are nonsignificant. 



Although it is, of course, quite conceivable that the sex ratio at birth 

 might be affected by prenatal irradiation — either through differential 

 mortality of one sex or through actual sex reversal (e.g., loss of one X 

 chromosome) — valid reports of such effects must to date be considered 

 lacking. 



Job et al. further claim that males are more susceptible to the induction 

 of abnormalities than are females. In the group irradiated between the 

 eighth and eleventh days, which yielded all the morphological abnormali- 

 ties reported, 37.4 per cent of 123 males and 24.8 per cent of 109 females 

 treated with 36-90 r were deformed. The difference is at the 5 per cent 

 level of significance (t = 2.07). The authors state, however, that only 

 one of the abnormal animals had been irradiated on the eighth day, the 

 other seventy-two between the ninth and eleventh, and the percentage of 

 males obtained following irradiation on these days (as given without 

 actual figures) is 61.6. The sex incidence of 62.7 per cent males among 

 the abnormals then seems as expected on the basis of random distribution. 

 The authors' claim must thus be considered unproved. Again, however, 

 it is quite conceivable that differential sensitivity of the sexes to the 

 induction of abnormalities will be found. 



4. MORPHOLOGY 



Even within the relatively limited literature on the subject a vast 

 number of abnormalities has been reported as resulting from the irradia- 

 tion of mammalian embryos during the period of major organogenesis. 

 It is, therefore, unfortunate that some authors failed to realize the impor- 

 tance of timing accurately the stage at which the embryos were subjected 

 to treatment, while others neglected to provide such pertinent informa- 

 tion as total numbers (for the calculation of percentage incidence) or 

 exact dosage. However, not many of the later publications fail in this 

 respect, and the earlier ones, which do, were nevertheless useful in demon- 

 strating that there existed a fertile field for future work. The earliest 



