RADIATION IN PRENATAL DEVELOPMENT 911 



in success of X-ray abortion is due to variability in the physical factors 

 of irradiation or to biological variability in the subjects cannot here be 

 determined, but it is clear, both from the animal results discussed in 

 earlier sections and the human cases summarized above, that damaged 

 embryos or fetuses do come to term in a large number of instances. Sur- 

 vival of these monsters is, moreover, fairly frequent. Murphy (1929) 

 found no stillbirths among seventy-four cases of postconceptional irradi- 

 ation which went to (or near) term; yet 34 per cent of the children were 

 grossly deformed. Postnatal viability may be estimated from the lists 

 of Goldstein and Murphy (1929) and of Schall (1933) : only 7 of 26 (27 per 

 cent) and 11 of 38 (29 per cent), respectively, of the malformed children 

 died between birth and two and a half years of age ; the rest, alive at the 

 last report, ranged from several weeks to twelve years with about two- 

 thirds of the group (in Schall's list) two or over. 



The possibility of damaging the human conceptus indirectly through 

 radiation injury of the mother has been stressed by Flaskamp (1929, 1930) 

 and by Faerber (1933), who report abnormal children following irradiation 

 during pregnancy to nonabdominal sites or with the uterus shielded. 

 Schall (1933) evaluates the four cases cited by Flaskamp and three addi- 

 tional ones and comes to the conclusion that, in at least five of the seven, 

 the uterus probably received scattered radiation. Results with experi- 

 mental animals (discussed earlier) make it likely that at least the 

 majority of the abnormalities are due to the action of radiation on the 

 embryo itself and would thus be avoided by appropriate shielding if non- 

 abdominal regions of a pregnant woman had to be irradiated. 



SUMMARY 



1. Radiation has proved to be an excellent tool in mammalian experi- 

 mental embryology and radiation-embryological studies on mammals 

 have yielded results which have important clinical implications. 



2. Most of the experimental work in the field has been concerned with 

 rodents and with radiation from an external source. Various degrees of 

 shielding and localization of the beam have been used, ranging from none 

 at all to the exposure of only selected parts of individual embryos. 

 Almost all of the early experiments, and even a few of the more recent 

 ones, suffer greatly from lack of timing of the developmental stage at 

 which radiation was applied. 



3. Recent experiments have shown that the stages at which radiation 

 is applied to the embryo can be conveniently grouped by broad end result 

 into (a) the preimplantation period, (6) the period of major organogenesis, 

 and (c) the period of the fetus. Experiments concerning these three 

 periods are reviewed in turn. 



4. Irradiation during the preimplantation period causes a high rate 



