896 RADIATION BIOLOGY 



complete inhibition of the very sharp rise which normally takes place at 

 birth: while control counts increase from 350 to 5800 by the tenth day, 

 irradiated animals stay at the fetal level except for a temporary rise to 

 1100 on the fifth day. The deficiency of polynuclear cells is somewhat 

 greater than that of mononuclear cells, the former averaging only about 

 29 per cent of the total white count for the period from birth to ten days 

 instead of the normal 43 per cent. 



2. MORPHOLOGY 



Irradiation during the period of the fetus does not lead to the striking 

 changes or malformations in newborns which are produced by irradiation 

 with comparable or even lower doses during the period of major organo- 

 genesis (Job, 1935; Kaven, 1938a; Russell, 1950). It is, however, 

 erroneous to assume that exposure during the latter part of pregnancy is 

 without morphological effects. It must be remembered that there is less 

 chance for any damage to express itself as a gross change by the time of 

 birth, for not only is the irradiation-to-observation interval shorter, but 

 the rate of development averages considerably less over that period than 

 over the interval from earlier exposure to birth. On these grounds, it 

 may be expected that gross changes will become expressed later in life and 

 these have indeed been reported by a number of authors (Bagg, 1922; 

 Kosaka, 1928e; Kaven, 1938a; Russell, 1950; Hicks, 1950; Grobman, 

 personal communication). Several studies on fertility point in the same 

 direction (Parkes, 1927; Kosaka, 1928e; Hanson, 1923). The immediate 

 damage which may lead to later gross changes was demonstrated by 

 Kosaka (1928b, c) and Hicks (1950). General growth retardation has 

 also been reported (Kosaka, 1928e; Job et al., 1935). Some of the studies 

 enumerated will be briefly described in the rest of this section. 



Delayed morphological effects of irradiation during the fetal period were 

 first noticed by Bagg (1922) in survivors from the group in which acute 

 radiation death had been described (see p. 893). Externally, these 

 animals exhibited opaque pupil and atrophied lens. At autopsy at about 

 a year of age, Bagg also noted smallness of the cerebral hemispheres, 

 especially the neopallium (occasionally even complete absence of the 

 cortex), and arrest of the gonads, ovaries and testes alike. Kosaka 

 (1928e) also found very marked hypoplasia of the cerebrum and the 

 gonads, and occasionally a smaller degree of arrest in lung, liver, heart, 

 and kidney in surviving mice (or rats ?) irradiated after the fourteenth 

 day postconception with % SED. Both Kaven (1938a) and Russell 

 (1950) report later development of skin defects and of cataracts resulting 

 from irradiation during the period of the fetus but it is not known whether 

 that period is critical for the production of these changes since mice 

 exposed earlier were not kept alive in large enough numbers after birth. 

 Working on the same Fi hybrid used by Russell, Grobman autopsied 



