, 2. portion of the division delay after moderate doses expressed as a block in Gy. More detailed comparis 25 will not be made here. It appears evident, howev that work on the naturally ~ynehronized cell syst: of dividing sea urchin eggs is pertinent to the prc lem of division delay in irradiated mammalian cells. The assistance of Regina Rigoni in carrying these studies is gratefully acknowledged. CONTROL DIVISION TIMES 14 -4- REFERENCES 1. Henshaw, P. 8. Further Studies on the Action of Roent; Rays of the Gametes of Arbacia punctulata. Am. Reentgenol. 48, 899-993 (1940). 0 i 10 a 20 1d 3000 40 i 50 ba 60 70 ! BO MINUTES AFTER FERTILIZATION Fic. 31-—The sensitivity to radiation-induced cleavage de- lay as a function of the postfertilization time Arbacta zygotes are irradiated. The dashed curve shows the effect of incubation at 15.2° C for 30 min right after fertilization. tion treatment. It is hoped that further study of the effects of various agents on the recovery and modification processes will lead to a better understanding not only of the processes themselves, but also of the underlying radiation response. Mitotic or division delay in mammalian cells also varies as a function of the time during the generation cycle irradiation takes place. The subject has been reviewed recently by Sinclair.? The form of response appears similar to that found chin eggs in that the maximum delay the cells are irradiated during the period thesis, S. For cells not irradiated in S, with sea uroccurs when of DNA synthe principal 2. Henshaw, P. 5. Studies of the Effect of Roentgen Rays the Time of First Cleavage in Some Marine Invertebr Eggs. I. Recovery from Roentgen-Ray Effects in Arba Eggs. Am. J. Roentgenol. 27, 890-898 (1932). 3. Failla, P. Reeovery from Radiation-Induced Delay Cleavage in Gametes of -irbacia punctulata. Science 1 1341-1342 (1962). 4. Failla, P. Recovery from Division Delay in Irradia Gametes of Arbacia punctulaia. Radiat. Res. 25, 331(1962). 5. Failla, P. Division Delay in Irradiated Gametes of . Urchins. Argonne National Laboratory Radiologi Physics Division Annual Report, July 1966 through J 1967. ANL-7360, p. 78. 6. Failla, P. Division Delay and Recovery in Irradiated : Urchin Gametes. Argonne National Laboratory Rac logical Physies Division Annual Report, July 1967 thro: June 1968. ANL-7489, p. 138. . Cormack, D. H. Site of Action of Ribonuclease during Inhibition of Egg Cleavage. Nature 209, 1864-1365 (19% 8. Rustad, R. C. and Burchill, B. R. Radiation-Indu. Mitotic Delay in Sea Urchin Eggs Treated with Puroms and Actinomycin D. Radiat. Res. 29, 203-210 (1966). ~I RADIATION- INDUCED CLEAVAGE DELAY IN MINUTES oo ho mar icle a ut oe aladsht 9. Sinclair, W. K. Cyclic X-Ray Responses in Mammal Cells in Vitro. Radial. Res. 33, 620-6438 (1968). THE RETENTION OF 3Ba IN BEAGLES J.E. Farnham and R. FE. Rowland Barium, like the other alkaline earths, is a bone-seeking element. These studies, which started some ten years ago, were designed to examine the whole-body retention and the plasma clearance of Ba’ in beagles of various ages, with the aim of comparing these parameters with the values found for calcium, strontium, and radium. This is the final report of this study. INTRODUCTION The retention of barium in the skeleton and in the blood, like that of the other alkaline earths, is of interest becauseit 1s closely related to the calcium metabolism of bone.“-® Knowledge of the differences and similarities in the metabolism of barium and calcium should elucidate the norma] processes of skeletal n tabolism. Furthermore, the chemical similarity barium and radiuminsures that extending our mea: knowledge of barium metabolism will contribute our understanding of the toxicity of radium in n. and animals. In June of 1959 we began a long-term study to me: ure the whole-body retention ofBa in two bea dogs over a period of several years. Progress data h: been given in three earlier reports. * ®) Subsequer we have injected three additional beagle dogs w the 13%Ba isotope to measure the short-term upt: and retention of barium, and to measure the radi