Many investigators have reported experimental malformations caused by different kinds of extrinsic factors acting upon the maternal animal during pregnancy and affecting various parts of the mammalian foetus, but few have described digital malformations in detail. In the author's experiments, digits in mice embryos and foetuses were studied after X-radiation of their mothers during pregnancy. The present paper will deal with:
(a) The relationship between the timing of X-radiation and the incidence of its resulting malformations.
(b) The relationship between dose and the frequency of the malformation, shown by an experiment carried out on the 12th day of pregnancy.
(c) The differences between the ddN- and the CF1-strains.
(d) The development of the digital malformations following irradiation.
The animals used were mice of the ddN- and the CF1 -strain, originally supplied by the Jikkendobutsu Chuo Kenkyujo, 90 days or older and weighing from 22 to 24 g. and kept at a room temperature of about 22–23° C. and 50–60 per cent. humidity.