RADIATION IN PRENATAL DEVELOPMENT 901 



observed poor postnatal development of the young. (This may very 

 well have been due to a disturbance of maternal lactation brought about 

 through radiation injury of the pituitary.) Driessen (1924), who irradi- 

 ated only the left half of the abdomen, found that the more severely 

 affected embryos were as often in the shielded horn as in the exposed one. 

 The work of Wilson and Karr (1950, 1951), in which only individual 

 implantation sites were exposed, should make it clear that a high inci- 

 dence of prenatal death can be caused, even with relatively low doses, by 

 direct action on the embryo, though indirect effects of certain degenera- 

 tive changes produced in the placenta (Kosaka, 1927) can even here not 

 be definitely excluded. The possibility of interaction between embryos of 

 the same pregnancy has not been considered in any experiment to date. 

 It is, however, quite conceivable that radiation-induced death of several 

 individuals within a uterus may adversely affect the remainder of the 

 litter, the viability of which was not directly influenced by radiation. 



As far as the production of abnormalities is concerned, there seems little 

 doubt that the maternal body need not act as an intermediary in causing 

 damage to the embryo, for similar changes have been produced in ovip- 

 arous forms. Moreover, in mammals, the methods of several investi- 

 gators, reporting a variety of malformations, have included shielding of 

 either the anterior half of the mother (Murphy and de Renyi) ; or of all 

 nonabdominal regions (Kaven; Warkany and Schraffenberger) ; or of 

 everything except a selected implantation site (Wilson and collaborators) ; 

 or part of an embryo (Raynaud and Frilley). In investigations where 

 part or all of the mother was exposed, it is, of course, not inconceivable 

 that a few of the embryonic abnormalities had an indirect causation, but 

 two pieces of circumstantial evidence, added to the evidence derived from 

 analogy with oviparous forms, make it likely that the majority of abnor- 

 malities are due to the action of radiation on the embryo itself: (1) since 

 "radiation sickness" of the mother is not sharply limited to a day, any 

 major influence of maternal pathological conditions on the development 

 of the embryo would presumably result in a much more blurred relation 

 between time of disturbance and effect than is actually encountered in the 

 well-defined critical periods (Russell, 1950) ; (2) it is unlikely that effects 

 via the mother would become apparent within 2 hours (Hicks, 1950, for 

 changes in neuroblasts). 



The only serious evidence against the above arguments is presented by 

 Job et at. (1935) who obtained only normal offspring (192) from 22 rat 

 females irradiated with shielding of the anterior half, while 23 other 

 females, irradiated in the same stages of pregnancy and receiving approxi- 

 mately the same dose of whole-body irradiation, produced 73 abnormal 

 young among 175. This result is puzzling in the light of later evidence 

 by Warkany and Schraffenberger, and by Wilson and collaborators, who 

 dealt with the same organism in comparable stages of pregnancy. 



