890 



RADIATION BIOLOGY 



70 per cent reduction in the number of germ cells in both sexes and some- 

 what reduced masculinization in the external genitalia of males, which 

 would point to the lack of some normally available trophic influence or to 

 a general toxic effect (e.g., in the blood) caused by the localized radiation. 

 The experiment of Kaven (1938b) forms a transition between those 

 concentrated on a particular stage and those concentrated on a certain 

 group of abnormalities. His concern was with the latter — namely, 

 meningocele and possibly related changes — but his earlier experiment 

 (1938a) had yielded information on the effective treatment stage. The 

 pertinent features of Kaven's experiment may be read from Table 13-6, 



Table 13-6. Incidence of Brain Abnormalities and of Mortality in Fetal 

 Stages and at Birth Foi lowing Irradiation of 7- or 8-day-old Mouse Embbyos 



(Kaven, 1938b) 



Irradiated day 7 



Day observed : 14 



Number of litters . 



Number of fetuses 



Per cent dead 



Per cent extrakranielle 



Dysencephalie 11 



Per cent meningocele" . . 



Average litter size: 



Total- 



Expected at term''. . . . 

 Found at term 



31 



237 

 65.8 



4.9 

 



7.6 



2.6 



17 



24 



182 

 72.0 







17.3 



7.6 

 2.1 



Birth 



39 



166 

 11.4 





 2.4 



4.3 



Irradiated dav 8 



13-16 



17-19 



40 



169 

 30.8 



3.4 

 19.7 



7.2 

 4.4 



Birth 



47 



219 

 13.7 





 16.1 



4.7 



Control 



Birth 



306 



2066 



1.7 





 



6.8 



a Percentages for prenatal observations are based on living fetuses only, in order to 

 make them more comparable with results at birth, when the majority of prenatally 

 dead animals will not be counted. 



b That is, living and without "extrakranielle Dysencephalie." 



which was compiled from information scattered through his paper. The 

 results show that brain hernias (more correctly, meningoceles) at birth 

 are significantly more frequent following irradiation on day 8 than on 

 day 7 (they were never obtained from later stages — Kaven, 1938a), and 

 that this abnormality becomes macroscopically apparent only late in 

 prenatal development (all cases but one after the sixteenth day). A find- 

 ing entirely unexpected from the birth data was the presence, in dissected 

 uteri, of fetuses with "icepack" brains, i.e., pseudencephalics. This 

 abnormality, referred to by Kaven as "extrakranielle Dysencephalie," is 

 about five times as frequent in 13- to 16- as in 17- to 19-day fetuses and 

 is apparently missing in litters not observed until shortly after birth. 



