RADIATION IN PRENATAL DEVELOPMENT 897 



twenty-nine mice 37-49 days old which had been irradiated with 300 r 

 on day 143-^ or 153^ postconception. He found reduction in size of 

 gonads and secondary sex glands, absence of the corpus callosum, and 

 absence of the gallbladder. Defects in the reproductive system could 

 also be produced by earlier irradiation (day 113^2, 123^, or 133^). 



Sterility has frequently been observed to result from irradiation during 

 fetal stages. Parkes (1927) raised twenty-five mice treated between days 

 10 and 18 postconception (mostly days 14 to 17). Only four of sixteen 

 females and neither of two males tested proved fertile. Kosaka (1928e) 

 found that, while irradiation between the seventh and thirteenth days did 

 not affect the fertility of survivors, irradiation after the fourteenth day 

 completely sterilized all but two males (totals not given). Even these 

 two (irradiated on the seventeenth day) were only temporarily fertile. 

 Sterility in all males was due to failure of sperm formation. Some 

 females too were completely sterilized but the majority was poorly 

 fertile and showed reduction in the number of mature ova formed. 

 Hanson (1923) mentions that "nearly all" rats (no numbers given) 

 irradiated in fetal stages proved sterile. Nurnberger (1920) found 

 sterility in the only one of his guinea pigs (a male) which survived the 

 early postnatal period. 



Two investigators have made observations on immediate effects of 

 irradiation during the period of the fetus. Kosaka (1928b, c) reports 

 findings on rat and guinea pig fetuses from fourteen and eighty-five 

 litters, respectively, sectioned 6, 12, 24, 48, 72 hours . . . (etc., to term) 

 after irradiation with ^-2 SED during the fetal period. In the rat, he 

 finds most tissue damage in the brain, retina, and thymus; liver and 

 spleen take second place, and skin third. In the guinea pig, results are 

 similar for irradiation in early fetal stages. Later in gestation, when the 

 guinea pig fetus is really comparable to a postnatal rat or mouse, brain 

 and retina lose some of their sensitivity but thymus remains in first 

 place. Hicks (1950) irradiated rat and mouse females in late pregnancy 

 (unfortunately without timing the stage of treatment) and observed the 

 resulting nervous system changes ^ to 96 hours after irradiation, as well 

 as at one day to several months after birth. He found 100 per cent 

 brain damage and usually also damage in the retina, cord, and ganglia 

 following doses of 200, 400, or 600 r. With 150 r, the degree and incidence 

 of damage was less; and no necrosis at all was found below 100 r. Acute 

 stages of necrosis were observable as early as 2 hours following irradiation. 

 The periventricular neuroblasts and other regions of rapid growth in the 

 brain, the neuroblastic layer of the retina, and the dorsal gray columns of 

 the cord were affected. Changes seen 2 to several days after irradiation 

 were classed as early malformations. These consist of the formation of 

 ependymal canals and rosettes in brain, cord, and retina, and are there- 

 fore interesting in comparison with the results of Kosaka, of Wilson, and 



