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haploid instead of two diploid micronuclei, tion division from these haploid. nuclei lack a number of chrdmosomes, i,e,, they are even more deficient than products from heavily irradi-' ated nuclei. As train was obtained which had one diploid and two- '. . haploid dcronuclei, and it was found that the meiotic products from ' the diploid survived almost t o the exclusion of those from t h e haplbid. Apparently, the gross chromosomal deficiency of the meiotic products from the haploid put them a t a .marked selective disadvantage as corn-' ' pared with the complete products from the diploid. This selective ' disadvantage was almost eliminated by a dose of 5,000 r of X-rays-. Probably the relatively small chromosomal deficiencies i n the meiotic Strains of Paramecium can be obtained.nhich have two c The products ofthe reduc-
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BIOLOGY AND MEDICINE products from an irradiated diploid nucleus are sufficient t o reduce them t o equality with the grossly deficient products from the haploid. Thus, selective processes may be important a t low doses of X-rays but probably cease t o be very important as t h e dose increases. Results of experiments on the effects of various enzyme inhibitors and chemicals on the repair or rejoining of radiation-induced chromosome breaks i n the seed of the bean Vicia w e r e as follows: (1). Any inhibition of cellular respiration inhibits chromosome rejoining' (2) The uncoupling of oxidative phosphorylation from respiration, %y treatment *th dinitrophenol, also inhibits re joining; nitrogen mustard indicated t h a t the dose levels of 5-10 micromole hours, which are commonly used on the growing roots of Vicia, are too strong t o be applied t o the seed, Radiation ProtectionStudies made of t h e effects of protective chemicals @-mercaptoethanol,.cysteamine) on t h e X-ray-induced reversion rate of several mutant strains of E, coli were paqticularly successful duced by use of a preplate treatment t&hnique with yeast extract liquid medium following cyst ed ne treatment and X irradiation, These studies show that the recovery process i n increasing postirradiation survival also decreases the mutation rate t o a corresponding degree, and suggest t h a t the phenomena of radiation-induced mutagenesis is indirect and related t o the mechanism of killing of cells.by X-ray. Efforts are under way t o develop a synthetic recovery medium adquate Conditions have been described under which Escherichia cold B / r a r e able partially to overcome the damaging effects of X- andy-radiation. Comparisons of protein and nucleic acid synthesis a r e now being made on irradiated and nonirradiated c e l l s under favorable and non-favorable conditions for recovery, Pre- results indicate synthesis of ' deoqribonucleic acid (DNA) is more sensitive to ionizing kadiations than either ribonucleic acid (RNA) o r protein synthesis. also indications that the optimal conditions for recovery may influence DNA synthesis more than BNA or protein synthesis,. radiation (cob lt-60 source), photosynthetic rates are measured by .70 t o 80% reduction i n photosynthetic rate with IO-minute exposures I n studies on effects of ultraviolet and y fixation of Cft 02. Experiments w i t h Thatcher wheat demonstrated a to ultraviolet (2537A) (at the particular geometry used) o r 100,000 r ~00,000r produced no further significant effect on the rate. chromatographic investigation of the distribution of Ca in photosynthetic products formed directly after irradiation showed a significant increase( i n glycine and serine and a decrease i n sucroseo ~ Increased exposures up to 30-min ultraviolet o r
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Pathology and Physiology. egakaryocytes and blood platelets of irradiated rats concentrated S304 in a manner similar to t h a t of the nonirradiated controls a t 1, 2, 3 , 4, and 24 days after 750-r sulfate by the surviving megakaryocytes and by platelets was-not affected by irradiation, it is probab& that platelets continue t o be derived from megakaryocytes remaining viable after irradiation. The distribution of Cab5 i n bone marrow cells and blood platelets was studied in rats. The activity of the platelets declined in a manner parallel to that of t h plasma, and the cells of the bone marrow did ' not concentrate the CaE5. These results indicate an absence of firm incorporation of calcium into the structure of platelets or megakaryThyroidectomy by injection of radioiodine was found to enhance ( p e 0.001) the survival of AK mice rendered leukemic by inoculation of * AK lymphoid leukemia cells. tion of the thyroid glandirasprevented by thyroid hormone. The beneficial effect afforded by destzucon nucleic acid synthesis in-chick embryos. into the adenine of deoxyribonucleic acid (ENA) was not altered by :&.' On the other hand, the specific activities of the DNA tbphe and guanine were lower following treatmentvrith 5000 r o r more. results suggest t h a t adenine of DNA may exchange with other adenine independently of new synthesis of DNA, whereas thymine does not enter into DNA except when net synthesis of the polynucleotide takes place. The data do not necessarily require classification of the guanine i n Studies were concluded on influence ofy irradiat'onII; The incorporation of C irrah tion of the embryos up t o 20,000 of cobalt-60 the same category as tme,