Effects of Continuous Radiation on Chick Embryos and Developing Chicks

THERE IS INCREASING demand for exact knowledge regarding the biological effects of continuous prolonged irradiation. The use of radioactive isotopes in medical therapy and exposure to radioactive substances in industry and scientific work (probably one of the greatest hazards today) presuppose such a knowledge, which actually is fragmentary and ill-defined. The following experiments were planned for the purpose of plotting out the effects, on different tissues, of large and small doses of radiation in relation to time intervals of exposure, and to establish the lethal threshold for cells of various types at different stages of development. Since very little work has been done with avian tissues, particularly in relation to the nucleated red blood cells, chicks were utilized. Materials and Methods The agent chosen was the radioactive isotope P32, and the subjects, chick embryos and growing chicks. The source of radiation, the isotope P32 (combined as KH2PO4 in an aqueous solution containing from 1,000 to 2,000 μc/c.c. of solution), has a half-life of fourteen days which insures sustained radiation.2 P32 emits relatively soft beta rays, half of them being absorbed by 3 mm. of tissue and all of them by 8 mm. of tissue. The chick embryo was an ideal subject for insuring continuous irradiation with measured amounts of radioactive material, since this could be administered easily by intra-yolk injections and there was no loss through excretion during incubation. All of our eggs were taken from the same flock of White Leghorns over a three-month period. Incubation was carried out under the usual conditions, 38 to 39° C, 70 to 80 per cent relative humidity. The incubation period varied from twenty to twenty-one days. To obtain an accurate and continuous picture of the radiation effects on the developing chick we used several groups of incubated eggs and chicks at various stages of development; each group was given a different dose of P32. The amount of radiation administered and the ages of the subject at injection and when killed are given in Table I. Our experiments may be divided into three groups. In the first group are the embryos given a single injection. A sterile solution of P32, as KH2PO4, was injected into the yolk from the fourth to the fourteenth day of incubation in amounts varying from 47.5 to 300 μc. In the second group are the chicks from one to thirty-seven days old given a single subcutaneous injection with approximately isotonic solutions of P32, as KH2PO4, in amounts from 115 to 1,050 μc. The third group consists of those chicks receiving multiple injections, the limits of total dosage being 180 μc. and 3,696 μc Chicks were killed by decapitation at intervals designed to give a continuous picture of the radiation effects.