IONIZING RADIATIONS: EFFECTS ON EMBRYO, FETUS 5 



ionizino; radiations, and. as Ions; as it survives, it too should accumulate 

 effects until an intolerable composite of the damasje would result in its death. 

 In the somatic cell, exposure effects short of lethality may not be so s^raphi- 

 cally demonstrable as those produced by a mutated oerm cell. Such a change 

 in the somatic cell might never be detected. There is as yet no direct proof, 

 but it may be conjectured that squamous cell carcinoma of the skin is more 

 likely to follow repeated, accumulated, but tolerable exposures, than a single 

 exposure. This presumption is based on the knowledge that squamous cell 

 carcinoma, which can be produced by ionizing radiations, can result from 

 tolerated exposures. 



The human embryo or fetus, and to some extent the adult, have powers of 

 sloughing off the undesirable or dead cells so that the only place that cumula- 

 tive effects can be detected is in the progeny of surviving somatic and germ 

 cells. This is why the low and tolerable exposures are so important. To kill 

 is clear cut. To maim for the duration of life may be biologically tolerable, 

 but psychologically and sociologically intolerable. 



Finally, one must emphasize the difference between the somatic and the 

 genetic effects. Since ionizing radiations can alter the central nervous system 

 either through the germ cells or through direct irradiation, we are concerned 

 with both genetic and somatic efTects. Neither is apt to be immediate; both 

 can be subtle and long delayed. 



When the embryo or fetus is inadiated it must be realized that both the 

 de\eloping central nervous system and the developing gonads of the organism 

 may have been exposed. Congenital effects resulting from direct irradiation 

 of the de\eloping organ primordia cannot have genetic corollaries except by 

 coincidence, which is \ery unlikely. Congenital effects following direct 

 irradiation cannot be inherited. However, concomitant with somatic exposure 

 there may be germ cell exposure which may well result in different and 

 possibly e\en more severe effects, but ones which cannot become apparent 

 until they appear in a succeeding generation. Somatic exposures alone may 

 alter the soma of one generation, but germ cell exposures may alter all suc- 

 ceeding progenies. 



Effects on the Embryo or Fetus 



In analyzing the embryonic effects one must have in mind lour special 

 situations: 



1. The medium of the embryo is acjuatic. and there is reason to believe 

 that this enhances its radiosensiti\ity. 



2. The embryo is a mosaic of acti\ely differentiating centers with con- 

 stantly changing but high mitotic indexes, both conditions enhancing radio- 

 sensitivity. 



