874 RADIATION BIOLOGY 



trol figures are cited, the operation itself may have contributed to the 

 prenatal death. It is otherwise hard to imagine how Warkany and 

 Schraffenberger (1947) could have obtained as large a yield as they did 

 with the very much higher doses of 190-1120 r. Summing all treatment 

 stages (days 9-15), 3 75 per cent of their 144 irradiated females had litters 

 at term and the average litter size was 5.26. Since results for different 

 doses are, in general, not reported separately, it is difficult to compare 

 stages. Table 13-5, however, makes it clear that, as in the mouse, there 

 is more prenatal death from irradiation of the earlier stages. In general 

 keeping with this trend is the report by Kosaka (1928b) that only }$ SED 

 suffices to kill all embryos irradiated during the "first stage" (days 5-10), 

 while during the second stage (days 11-15) 1 SED is required to produce 

 100 per cent mortality. Similar results are obtained in guinea pigs 

 (Kosaka, 1928c). In over-all sensitivity, Kosaka's rat embryos appear 

 intermediate between those of Job and those of Warkany. 



In summary, it may be stated that extensive data on the mouse reveal 

 that, for comparable doses, irradiation during the period of major organo- 

 genesis causes considerably less prenatal death than does treatment 

 during the preimplantation period. Furthermore, within the period of 

 organogenesis, susceptibility to prenatal killing probably decreases fairly 

 rapidly with embryonic age. This is shown by the mouse results as well as 

 by individual investigations on the rat, although the latter differ greatly 

 amongst themselves with regard to absolute sensitivity of the embryo. 



b. Neonatal. Only two investigators have reported in a quantitative 

 manner on death at birth following irradiation during the period of 

 organogenesis. In both cases, this is more frequent than prenatal death 

 observed by them in the same sample. Kaven (1938a) reports stillbirth 

 of over three-fourths of those newborns which had been irradiated 

 on day 10, 11, or 12 postfertilization with 178 r. Irradiation on the 

 immediately preceding or following day results in a smaller proportion 

 of death at birth. 



A pooling of several experimental series (involving different genetic 

 strains) by Russell and co-workers is represented in Fig. 13-2. This 

 shows that, while 100 r and below has no effect on survival at birth, 200 r 

 (a dose comparable to Kaven 's) applied on any one of days 7% through 

 11}-^ inclusive causes neonatal mortality, with a sharp peak for days 9^ 

 and 103^ (75 and 67 per cent respectively). Raising the dose to 300 r 

 increases neonatal mortality in general, the curve paralleling the 200 r 

 curve and the peak reaching 100 per cent (days 9}£ and 10^2) • These 



3 Throughout this review an attempt will be made to name the stage according to 

 the actual time elapsed since fertilization — a procedure which is followed in the 

 publications of Wilson, and of Russell et al. Following this system, Warkany and 

 Schraffenberger 's "10th day" will be referred to as day 9 (if irradiation took place 

 in the afternoon, it was day 9J><$), e tc 



