16 ROBERTS RUGH 



TABLE IV 

 X-Irradiation of the Early Mouse Embryo * 



^ 



c< 



iii 



i^ 



0.5 52 58 42 



1.5 90 95 5 



2.5 95 73 24 3 



3.5 76 88 9 3 



4.5 53 92 8 



5.5 37 77 17 6 



6.5 77 92 8 



7.5 25 96 4 



8.5 51 96 4 



9.5 12 90 10 



568 85.7 12.3 2.0 



" This table gives data from an extensive study of the effect of 50 r x-iays on the mouse embryo at 

 various days from 0.5 to 9.5. In any somatic study 50 r would be considered a low level exposure, but 

 from this study, when such an exposure kills 42% of the embryos at 0.5 days and large percentages at 

 2.5, 5.5, and 9.5 days, it is obvious that 50 r to the early developing mouse embryo is a high level 

 of exposure. Of course, exencephalia was produced, the largest per cent being at 5.5 days. 



Figs. 21-27 are on pages 14 and 15. 



Fig. 21. An enlarged \'iew of exencephaly (brain hernia) in the mouse. This is a 

 protrusion of the mesencephalon through the cranial roof. 



Fig. 22. Three members constituting an entire littt r, all .showing severe exencephalic 

 maldevelopment. This followed exposure of 50 r at 2.5 days. 



Fig. 23. Note the same group of 3 congenital anomalies in a field including a 

 normal control mouse fetus of the same age. This demonstrates that in addition to 

 congenital anomalies there is often a stunting of the irradiated embryos. 



Fig. 24. This shows an entire litter, as found in the bicornate uterus of the mouse 

 at 18.5 days, following an exposure of 200 r at 8,5 days. Note that 5 of the 11 litter 

 members exhibit exencephalia. 



Fig. 25. This shows 4 members of a litter exposed to 50 r at 3.5 days. These are 

 to be compared with a single control above. Note not only congenital anomalies but 

 stunting of every member. 



Figs. 26 and 27. These mice were exposed to 50 r fractionated to 25 r each at 

 two times during embryonic development, one exposure occurring before implantation 

 and the second after implantation but before the completion of neurogenesis. Note the 

 bizarre form of the extruded mesencephalon. The 2 litter members appear to be normal 

 but are stunted. 



