Florence Heys

An Analysis of the Effects of the Different Rays of Radium in Producing Lethal Mutations in Drosophila

EXPOSURE of fruit flies to radium rays produces both lethal and visible mutations. With heavy treatment the lethals are so numerous as to lend themselves to exact quantitative analysis. Hanson and Heys2 showed that when flies were treated for six hours with 140 milligrams of radium the percentage of lethal mutations was S.2 per cent. And, further, that when the alpha and beta rays were completely absorbed by a lead filter the gamma rays alone produced 2.8 per cent. of lethals, although in this latter case it is highly probable, in the light of work reported below, that it was a secondary radiation of beta particles produced by the passage of the gamia rays through matter that was the effective agent in causing mutations. In unpublished work on visible mutations due to radium rays it has been found that the gene mutations are, in general, in the same direction and of the same nature as those occurring spontaneously in the fruit fly and also parallel exactly the results obtained by Muller3 with X-rays. Darwin-and most writers on evolution since-have emphasized the importance of discovering the cause or

Duration of the Effects of X-Rays on Male Germ Cells in Drosophila melanogaster

DURING the past two years it has been abundantly established by Muller,2 Stadler,3 Weinstein,4 Whiting,5 Hanson and Heys6 and others that X-rays and radium produce gene mutations in the several organisms studied. In Drosophila both visible and lethal mutations result from such treatment. In Mullers earliest experiments the flies which hatched from eggs laid seven to twelve days after raying of the sperm which fertilized them showed the same percentage of mutations as those hatching from eggs fertilized by sperm during the first six days following treatment. This raises the interesting problem of the duration of the effects of irradiation upon mature sperm and also whether there is a differential effect of the same dose upon the various stages of spermatogenesis. The first of these questions has been answered by some experiments of B. B. Harris, of the University of Texas. Dr. Harris has kindly allowed me to refer to his results in advance of their publication. He found that when sperm are aged in the male and no copulation allowed

On Ovarian Regeneration in the Albino Rat.

Numerous cytological papers on germ cell origin have led to the view that the primordial germ cells are not the ancestors of the functional germ cells, although work is not lacking in which the older view is upheld that germ cells form a continuous stream throughout the individual life cycle and from generation to generation. Davenport, 1 spaying mice, found that, after a lapse of from 8 to 45 weeks, regeneration of the ovary occurred in 64% of his animals. Complete removal of the ovary was claimed, but cytological evidence was not secured in support of this. Macroscopic examination of masses of tissue at or near the site of the operation was the criterion for regeneration of the ovary. Haterius 2 secured 4 cases of regenerated ovarian tissue in mice out of 76 operations, and attributed these to incomplete ovarian extirpation. Parkes, Fielding and Brambell 3 had 121 cases of double ovariotomized mice. After ovariotomy the oestrous cycle (vaginal smear method) ceased. But in 11 cases spontanoeus oestrus subsequently occurred, and this was taken to indicate regenerated ovarian tissue. In 8 of these 11 cases the presence of new ovarian tissue was demonstrated histologically. We are able to add data of a similar nature from the albino rat. Both ovaries were removed from 105 rats and each ovary preserved for sectioning. The animals ranged in age from 10 to 200 days at time of operation. The period allowed for regeneration ranged from 90 to 180 days. There were 8 cases of ovarian regeneration as determined by sectioning the regenerated masses of tissue. The 8 original ovaries removed from these sites of regeneration were then sectioned to determine whether the whole ovary had been removed.

Radium and Lethal Mutations in Drosophila Further Evidence of the Proportionality Rule from a Study of the Effects of Equivalent Doses Differently Applied

Experiments planned with a view to determining within what limits the proportionality rule holds show again a strict correspondence existing between the amount of radium administered and the consequent biological effect, the induced mutation frequency obtained varying directly with the dosage. A series of dosages as nearly exactly equivalent as possible but applied in different ways gave approximately equivalent results, dependence being merely upon the total energy absorbed. Whether the treatment consists of a high intensity and a short exposure or low intensity and long exposure the dosage expressed in r-units is remarkably constant. Within the limits set for the present investigation (2 mgms radium for 150 hours to 300 mgms radium for 1 hour) a small amount of radiation does not seem to have a disproportionately great effect owing to its being applied over a long period of time. Perhaps disproportionality begins outside even these wide limits, and, if so, there is still a possibility that a small amount of natural radiation acting over a very long time might be sufficiently effective to account for natural mutations.

The Relation of the Induced Mutation Rate to Different Physiological States in Drosophila melanogaster: I. Irradiation After Starvation

In two series of experiments, one in which male Drosophila were treated and one in which females were treated, flies hatched from cultures having minimum food supply and completely starved for a period of 8 hours preceding treatment were given an exposure of 300 milligram hours, gamma radiation only. The results obtained differ significantly in two respects from those in unstarved treated controls: sterility of the parent and F1 generations and lethal mutation rate. Mortality in the starved parent generation, based on the number dead by the second day after exposure, was high as compared with no mortality in the treated controls. The percentages of sterility in both generations and the rate of lethal mutation were significantly lower. Possibly these results may be explained by the fact that the cells of starved tissues are less actively dividing and perhaps, therefore, less susceptible to the effects of radiation. The authors take this opportunity to acknowledge, with appreciation, efforts of Professor E. Faure-Fremiet, of the College de France, in securing laboratory space in which to carry on the experimental work and to thank him for his constant interest in its progress. We take pleasure also in expressing our appreciation to Dr. A. Lacassagne, of the Radium Institute, and to the Radiological Clinic of the Curie Foundation for arranging the radium treatments.

Experimental Transmission of Saint Louis Encephalitis to White Swiss Mice by Dermacentor variabilis.

Summary 1. The virus of Saint Louis encephalitis was recovered from the bodies of engorged larval ticks which had fed in infected adult Swiss mice. 2. Under experimental conditions the Saint Louis encephalitis virus was transmited to young Swiss mice by larval ticks. 3. Normal adult mice upon which infected, full-grown ticks had fed developed considerable resistance to intracerebral inoculation of virus.

The Relation of the Induced Mutation Rate to Different Physiological States in Drosophila Melanogaster: II. Irradiation during Complete Anesthesia

In preliminary studies of the physiology of mutation production, males and females of Drosophila were irradiated during complete anesthesia by di-ethyl ether. Unlike the results reported in the first paper of the series where the flies had been irradiated after starvation, both males and females exposed under anesthetic to gammaradiation of 300 milligram-hours showed no mortality in the treated parent generation, but gave high percentages of sterility and a high rate of lethal mutation as compared with treated controls. In controls exposed to anesthetic alone no signs of sterility were observed, and no lethal mutations occurred. There was a slight difference in the response of the two sexes to identical conditions of irradiation, the females being consistently a little less sensitive. These differences are, however, not statistically significant. The experiments are being continued with a view to analyzing just how the effect is produced and to determining to what extent the results obtained are due to increased sensitivity of the gonadial tissues and to what extent, if to any, to mechanical effects. The authors take pleasure in expressing their appreciation to Drs. A. Lacassagne and G. Gricouroff, of the Radium Institute, and to the Radiological Clinic of the Curie Foundation for arranging the radium exposures.

DOES REGENERATION FOLLOW COMPLETE OVARIOTOMY IN THE ALBINO RAT

These two experiments seem to show that in the rat it is easily possible to be certain of getting out the entire ovary in young rats (under forty days old) and that upon complete removal no regeneration occurs.