One of the outstanding features of radiation damage is the difference between embryonic and adult tissues and their reactions and the manner in which these reactions are manifested (Hicks*; Russell4; Wilson and Karr5; Wilson, Jordan, and Brent,6 and Warkany and Schraffenberger7 ). The sequence of x-ray-induced developmental abnormalities and a strict timetable of their genesis have been established in rats and mice by Hicks.3 He demonstrated a certain resistance of the embryonic tissue toward x-ray doses in the range of 100-200 r during the first eight days of gestation. No measurable damage resulted, and the newborn rat appeared normal. Doses ranging from 300-400 r and administered to the rats during the first eight days either destroyed the embryos or resulted in normal newborn rats. The same doses applied at a later time led to definite developmental defects.
In Anderson's textbook of "Pathology,"8 the lymphoid tissues,