[Analysis on x-ray-sensitivity of rabbit embryos (author's transl)]

The sensitivity of Day-4-blastocysts to total x-ray irradiation at a dosage of 130r is studied at developmental stages 10, 11, 12 and 17 days p. c., after the treated blastocysts could develop in synchronized foster mothers. The effects by 130r are compared to normal controls and other dosages of 90r and 250 r. A maximum of developmental failure is recorded particularly in 130 r --irradiated embryos. The following reasons are considered to being causally involved: 1. Reduced mitotic activity between Days 5 and 7. 2. Reduced growth of the embryonic disk at Days 6 and 7, such inhibiting differentiation and further formation of the embryo. 3. Increasing imbalances in the essential synchronisation demands of the embryonic and maternal systems. 4. Developmental retardation accompanied by a failure in the dissolution of the blastocyst coverings, by this resulting in a considerable number of degenerating blastocysts at Day 8 p.c. 5. Increased imbalances in the ratio of the differentiation and growth, specific for each embryonic stage. Growth of the embryo, in general, occurs more slowly than the process of differentiation. 6. Failure of adaptation to the chorionic-allantoic-placenta supply at Day 11. This investigation may be considered as a basis for further causal relationship studies to find out the reason for the more pronounced sensitivity to 130 r than to 250 r of Day 4 rabbit blastocysts.