A mathematical model of a phantom simulating the body and major internal organs of a Japanese adult has been developed for use in computer calculations of radiation dose. The total body height of the mathematical phantom is 162 cm, and the total body mass is 55 kg based on densities of 0.3, 1.4, and 1.0 g/cm³ for the lung, skeleton, and bulk tissues of the body, respectively.

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Rate constants for reactions of hydroxyl radicals with nucleosides and related compounds were determined by a p-nitrosodimethylaniline method. The obtained rate constants of nucleosides were found to be generally smaller than the sum of those for free bases and ribose, of which the nucleosides are composed. An attempt was made to explain the reduced reactivity of nucleoside in terms of steric hindrance of reaction sites due to other part of the same molecule. The steric hindrance was estimated by solid angle admitted to the radical attack. The observed reactivity was found to be well interpreted by the calculated reactivity according to the following equation,
k_nucleoside =ƒ₁k_base + ƒ₂k_ribose
where ƒ₁ and ƒ₂ are steric factors estimated from the solid angles.

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The whole-body retention of ⁶⁰CoCl₂ and ⁵⁸Co-cyanocobalamin after oral and intravenous administration was investigated in young and adult rats. The whole-body retention of ⁵⁸Co-cyanocobalamin was considerably higher than that of ⁶⁰CoCl₂ in rats of all age groups and the younger rat showed higher retention of both CoCl₂ and cyanocobalamin than the adult rat. The biological half life in slowly decreasing phase after oral administration of ⁶⁰CoCl₂ and ⁵⁸Co-cyanocobalamin was approximately equal among all age groups and estimated to be about 10 and 25 days, respectively. These results suggested that the whole-body retention of orally administered ⁶⁰CoCl₂ and ⁵⁸Co-cyanocobalamin in rats of various ages depends mainly on the intestinal absorption rather than endogenous excretion rate. The excretion pattern of ⁵⁸Co-cyanocobalamin, i. e., F/U ratio etc., is very different from that of inorganic cobalt and it is therefore assumed that ⁵⁸Co-cyanocobalamin is rather stable in the body.

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Ultraviolet light (UV) irradiation of vegetal hemispheres of many anuran eggs results in an elimination of primordial germ cells in the tadpoles. Quantitative studies were performed on this phenomenon. In this report, UV irradiation experiments were performed on the eggs just before the first cleavage division, and a dose-response curve was obtained at the stage. The results supported the probabilistic model for germ cell determination process, previously presented by the authors.
Cell diameter analysis suggested that the germinal plasm-containing cells (i. e. presumptive primordial germ cells) divide at the same rate as ordinary endodermal cells during stage 10-33. This led to a calculation of the doubling time of presumptive primordial germ cells, odtaining its value as about 30 hrs at 20°C. Finally, a scheme for the proliferation kinetics of germ cells in Xenopus laevis embryos was presented.
Several UV experiments on the vegetal hemisphere of anuran eggs have presented favorable evidence that histologically identifiable germinal plasm contains the UV-labile germ cell determinant. Their significance was also discussed.

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Various statistical models designed to determine the effects of radiation dose on mortality of atomic bomb survivors in Hiroshima and Nagasaki from specific cancers were evaluated on the basis of a basic k(age)×c(dose)×2 contingency table. From the aspects of application and fits of different models, analysis based on the additive logit model was applied to the mortality experience of this population during a 22 year period from 1 October 1950 to 31 December 1972. The advantages and disadvantages of the additive logit model were demonstrated.
Leukemia mortality showed a sharp rise with increase in dose. In particular, the dose response relationship suggests a possible curvature as the log linear of the dose estimated to be more than 600 rad was set arbitrarily at 600 rad and then the average dose in the 200+ rad group would change from 434 to 350 rad. In the 22 year period from 1950 to 1972, a high mortality risk due to radiation was observed in survivors with doses of 200 rad and over for all cancers except leukemia, cancer of the gastrointestinal tract, lung cancer, cancer of respiratory system and other cancers. On the other hand, during the latest period from 10, 65 to 1972 a significant risk was noted also for stomach and breast cancers. Survivors who were nine or less in age at the time of the bomb (ATB) and were exposed to high doses of 200+ rad appeared to show a high mortality risk due to all cancers except leukemia, although the number of observed deaths is yet small.
A number of interesting areas are discussed from the statistical and epidemiological standpoints, i. e., the numerical comparison of risks in various models, the general evaluation of cancer mortality by the additive logit model, the dose response relationship, the relative risk in the high dose group, the time period of radiation induced cancer mortality, the difference of dose response between Hiroshima and Nagasaki and the relative biological effectiveness (RBE) of neutrons.

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