336 RADIATION STANDARDS, INCLUDING FALLOUT present. Ever since 1915, abnormalities of this same kind had been known in fruit flies and had been found to be increased in frequency by radiation. They havealso been described more recently in connection with certain abnormal types in mice. These errors of chromosome number, which might be called a sort of mutation, arise in two general ways. The commonest is probably what is called nondisjunction; that is, the failure of two matched chromosomesto separate from each other and go singly into the reproductive cells. The result would be formation of one reproductivecell with an extra chromosome and another with one chromosometoo few. The other way in which such errors arise is through the loss of the chromosome from thefertilized egg. Recent studies at the Oak Ridge National Laboratory by Liane Russell and C. L. Saylors show that when a sperm of the mouse is irradiated, it is usually this second sort of error that occurs, 100 roentgens yielding 5.2 percent of cases of Joss of the sex chromosome from the newly fertilized egg, but only about 0.2 percent when the sperms are irradiated before fertilizing the egg. Losses of other chromosomes than the sex chromosomesare fatal mm early development in the mouse and presumably in humans losses of most chromosomes except the sex chromosomes and the smaller chromosomes of other sorts are likewise fatal. Many are now known to cause multiple congenital defects resulting in neonatal death. In any event, in addition to the previous estimates of mutations arising from a given dose of radiation, we must now add something for this novel and previously unsuspected type of human damage. At the present time one cannot say how many mongoloid idiots and sexual aberrant types have been produced by radiation. It may indeed be a small proportion of the total. Yet until we know more about the relation of these conditions to radiation dosage, we must be exceedingly cautious, for there is no reason to doubt that radiation will cause such defects, particularly if administered to the female or her just-fertilized egg cell. Until quite recent years all radiation exposures in genetic investigations were for some reason restricted to males. Gradually evidence began to accumulate from fruit fly experiments to show that just as there are differences in sensitivity between immature and mature reproductive cells in a single sex, so, too, there are differences in sensitivity to radiation between the male and female reproductive cells. W. L. Russell at Oak Ridge has nowobtained information bearing on the production of mutations in the oocytes of female mice. <Although the data are still insufficient or scanty, it appears at present that at a high dose rate—80 to 90 roentgens per minute-—the female germ cells are more sensitive than spermatozoa, whereas at a low dose rate—90 roentgens per week—they yield even fewer mutations than the male germ cells do. Moreover, there is some indication that the mutations in the female germ cells differ qualitatively from those in the male germ cells. Clearly, if an adequate idea of the sensitivity of a population to radiation is to be obtained, we will need to have sufficient data on both sexes and forthe entire lifespan. The most. unexpected and most discussed development during these recent years in the study of mutations produced by radiation has been the demonsiration by W. L. Russell and his Oak Ridge colleagues SGRRSRIRITIERCCsousHebetsOYpieah ieeeEgae