³²P-retention in DNA was enhanced with increasing irradiation time when wet DNA was irradiated at -78°C. This suggested an extreme complexity of the mechanism underlying the retention. Thus, the effects of various solvents on the retention were examined as an approach to the elucidation of the mechanism of ³²P-retention. When DNA was irradiated with alcohols, ³²P-retention in DNA was decreased markedly. This suggests that hot ³²P atoms were caught by alcohols or alcoholoriginated radicals to yield the acid soluble fraction. From the experiments in which the other organic or inorganic compounds were added, the mechanism of ³²P-retention in DNA was discussed.

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Experimental study on the behavior of uranium on soils was carried out using three kinds of soil; volcanic ash, alluvial and sandy soils. The results are as follows ;
1) Uranium dissolved in water (1-100 μeg as U/ml) was almost completely adsorbed on every soil examined.
2) The desorption of uranium from soil with salt solutions was extremely difficult especially from volcanic ash soil.

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Aqueous solutions of catalase were irradiated with ⁶⁰Co gamma-ray. Protective action of adenosine and its derivatives was examined under the conditions where the yield of the enzyme inactivation was independent upon the initial concentration of the enzyme. By increasing the concentration of the protective substance, a maximal protection was observed. The level of the maximum was dependent on the chemical structure of the protective substances. Addition of excess amounts of adenosine decreased the effectiveness of its N₆-hydroxyethyl derivative which was more protective, by itself, than adenosine. Based upon these observation, it was assumed that the binding of the protective substance to the enzyme molecule was the basis of the protection of the enzyme.

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A basic substance was obtained from calf thymus by acid extraction and further purified by CM-cellulose column chromatography. The material showed a significant prolongation of survival and a promotion of recovery of lymphoid tissues of mice exposed to lethal dose of ionizing radiation, when administered intraperitoneally 10 minutes before irradiation. Furthermore, it was capable of inhibiting the occurrence of radiation-induced leukemia in mice. The most active material (CM3), purified by CM-cellulose column chromatography accelerated the recovery of nucleated cells of bone marrow in irradiated mice. This active fraction, CM-3, was found to be stable after heating at 100°C for 15 minutes and a basic protein with molecular weight of approximately 20, 000.
We also obtained similar fractions from calf liver and spleen by the same extraction procedure. The spleen extract showed the survival effect to some extent in irradiated mice, but the liver extract was ineffective.

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The fate of HeLa cells irradiated with X-rays and fast neutrons was followed by cine and continual photographic procedures. The following interestings were made through detailed analysis of the films.
(1) No differences could be observed between X and neutron irradiated cells as to the types of cell abnormalities as well as modes of cell disintegration.
(2) Cell fusion played an important role in reproductive cell death. Furthermore, cell fusion was observed between cells other than sisters, cousins, aunts or nieces.
(3) In the pedigree of cells with colony-forming ability, these was a tendency for both cell death and normal cell division to occur in clusters of closely-related cells.

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Studies on translocation of ionic and colloidal ³²P in gravid mice show that placental discrimination against the former is negligible in comparison to the latter. Ionic ³²P is deposited in fetus against a concentration gradient. An important feature of the distribution of radiophosphorus in maternal tissues is that the colloid is localized predominantly in liver with the other tissues having considerably less radionuclide burden whereas ionic ³²P is distributed more or less evenly in the tissues. The accumulation of ionic ³²P in tissues of pregnant mice is greater than in the tissues of non-pregnant mice and vice versa with respect to colloidal radiophosphorus.

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Egg-white lysozyme was irradiated in 0.5% aqueous solution with cobalt-60 γ-rays. The resulting samples were fractionated by gel-filtration of Sephadex G-100 and treated with mercaptoethanol in order to clarify the polymerization caused in radiation-inactivated lysozyme.
Gel-filtration pattern of irradiated lysozyme revealed two protein fraction. The first peak of them showed no enzyme activity and higher molecular weight than intact lysozyme. The second corresponded to intact lysozyme. Mercaptoethanol-reduction studies showed the conversion of inactive polymerized component of irradiated lysozyme into a form derived from intact lysozyme by this treatement.
These evidences suggest that a large part of inactivation of lysozyme by γ-ray irradiation proceeds in a polymerization caused by intermolecular disulfide bond and the polymerized component is responsible for radiation-inactivation of lysozyme.

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Leakage γ-ray energy spectra up to about 9 MeV were measured by using of a 3"φ × 3"L NaI (TI) scintillation counter at two points in the reactor room of KUR (Kyoto University Reactor), and leakage low energy γ-ray (between 10 and 200 keV) spectra were also measured at the reactor power of 5 MW by using of a measuring system which consisted of a 25 mmφ × 2 mm thick NaI (TI) scintillation counter, a collimator, and a logarithmic amplifier.
Distinct peaks were not found in the observed γ-ray energy spectra up to 9 MeV except O W. In the case of O W, the distributions in the spectra were not found in the energy range above 2.8 MeV.
Peaks at the energies about 200 keV and between 60 and 100 keV were found in many low energy γ-ray spectra. The energy of the former peak corresponds nearly to single back-scattered γ-rays (scattering angle θ, 180°), and the latter one to multiple-scattered. The low energy γ-rays which leaked directly through the shielding wall of the reactor were observed below 30 keV. It was considered that low energy γ-rays leaked through the shielding wall were comparatively weak in intensity, and that high energy γ-rays, when leaked, became to low energy by scattering in the air.

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There is no conversion of λ DNA into the twisted circular form DNA molecules when E. coli cells were infected with ultraviolet-irradiated λ phages.

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