SEGMENTARY HETEROCHROMIA IN FOETUSES 



249 



(iii) The frequency of heterochromia of the iris is much greater among 

 irradiated than among non-irradiated, x^ is 36 for one degree of freedom 

 (after Yates' correction). 



4. Time of irradiation 



The time distribution of irradiation among the heterochromic children is 

 strilvingly different from that of the general irradiated population. 



Table II shows a highly significant cluster of heterochromia for an irradia- 

 tion age of 4 to 6-9 months in utero. This does suggest the existence of a 

 sensitive period, a fact largely established in embryology. 



Table II. The age of the foetus at the time of the irradiation in utero. The 

 distribution among children of the second enquiry is very comparable to that of the 



first 



5. Dose of irradiation 



Due to the mode of ascertainment, all radiological procedures are known 

 precisely, at least with the accuracy of the transcription. The calculation of a 

 mean dose is thus possible, with a general restriction concerning its precision. 



From the actual data we can conclude that the mean probable dose 

 received by the whole sample is of the order of 2 to 3 r. The mean dose 

 received by the children showing heterochromia is also of the order of 2 to 3 r. 



The main interest of these findings is, in our opinion, to show that even 

 smaU doses of radiation have a somatic effect, which can be detected if 

 induced at a sensitive period of embryonic development. 



