RADIATION IN PRENATAL DEVELOPMENT 909 



given, among others, by Robinson (1927 — twenty-three cases collected 

 from the literature), Lacomme (1931 — two cases), Jones and Neill (1944 — 

 seven definite and twenty-eight questionable cases), and Hobbs (1950 — 

 one case), and have been stressed by various authors as showing that 

 damage need not invariably or even frequently follow prenatal irradiation, 

 there can, of course, be no question, both from experimental and clinical 

 findings, that the human embryo is subject to severe radiation injury. 

 The types of human abnormalities enumerated in the case literature 

 include microcephaly, blindness, microphthalmia, coloboma, cataract, 

 chorioretinitis, ankyloblepharon, strabismus, nystagmus, mental defi- 

 ciency, hydrocephaly, coordination defects, mongolism, spina bifida, 

 skull malformations, ossification defects of the head, cleft palate, ear 

 abnormalities, deformed arms, club feet, hypophalangea, genital deform- 

 ities, and general mental and physical subnormality. Microcephaly is 

 present alone or in combination with other changes in 16 of 28 abnormal 

 cases listed by Goldstein and Murphy (1929), and in 27 of 38 tabulated 

 by Schall (1933). It is probable that this classification includes a 

 variety of head abnormalities. Next on the list in Schall's tabulation 

 are various eye defects (14 of 38 cases). Central nervous system abnor- 

 malities other than microcephaly are frequent as a group. Thus, the 

 tissues believed to be radioresistant in adult humans are especially sensi- 

 tive in the embryo. 



By equating human and mouse gestation periods developmentally 

 (rather than chronologically, since, e.g., the first one-fourth of mouse 

 prenatal life is equivalent to only the first one-thirtieth of human) , as has 

 been done by Otis (1952), it should be possible to predict when the 

 critical period for the production of abnormalities determined in the 

 mouse (see preceding sections) should occur in man. This type of predic- 

 tion is substantiated by one of the few human cases where stage of irradia- 

 tion is accurately known (Feldweg, 1927) : irradiation during the fourth 

 or fifth week caused arm abnormalities of the newborn similar to those 

 which can be produced in the mouse by treatment at the corresponding 

 stage, day 10^2- The period of major organogenesis in man, correspond- 

 ing to days 6^ to 13^2 m the mouse, comprises weeks 2-6. It may be 

 predicted from the animal results that irradiation during those stages will 

 lead to a high percentage of conspicuous abnormalities, while later 

 irradiation will yield a lower incidence, at least insofar as immediately 

 recognizable changes are concerned. Confirmation comes from the 

 tabulation of Kraemer (1930) who found that all of 11 cases of irradiation 

 within the first two months resulted in damage, while only 7 out of 11 

 (64 per cent) irradiated between the third and fifth months and 3 out of 

 13 (23 per cent) irradiated between the sixth and tenth months were 

 abnormal at or near term. In Schall's (1933) tabulation, which, in 

 contrast to Kraemer's, lists only positive cases, 57 per cent (20 of 35) were 



