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Medical examinations were carried out on the spot on 3, 076 persons of dust-producing worksnops in Gunma Prefecture, and 306 cases (9.98%) were found suffering from silicosis.Distribution of the grade of the disease was as follows : 214 (6.97%) of grade I, 66 (1.96%) of grade II, 19 (0.62%) of grade III, and 13 (0.43%) of grade IV.The order of the incidence rate for different kinds of work was earth and stone work (the highest) lignite mining work, and metal work.In all kinds of work, the incidence rate increased with increase in age and years of occupation.

With rats of Wistar strain, investigation was made on change in I131 uptake by the thyroid produced by local X-ray irradiation on it, and the following results were obtained :1) I131 uptake by the thyroid (30 minute value) declined in both sexes in parallel with the dose of the irradiation. The decrease was significant when the dose was 1000 and 6000r.2) Temporal change in the I131 uptake was followed for 2 hours after the irradiation and it was found that in a dose of 200 r no difference was observed from controls, but that in doses of 1000 and 6000r, the uptake showed significant decrease from control values. And the decrease was nearly in parallel with the dose of the irradiation.3) Temporal change in the I131 uptake (30 minute value) during 24 hours after the irradiation varied according to the dosage.4) Relatively long observation (2 hours to 7 days) of the I131 uptake (2 hours value) after the irradiation in doses of and 1000 and 6000r revealed that the uptake was inhibited in the early period, but that later it was conversely increased.

As experimental materials we used solutions of dyes belonging to tryphenyl methan, azo anthraquinon. cyanin, thlazin and nitro groups, which were irradiated with the following results : The colors of aqueous and chlorform solutions of these dyes faded or changed when irradiated with X-ray, the latter being sensitive more markedly. This can be attributed to the indirect action of Cl-base which is produced from chloroform. Cyanin and aminoazobenzene dyes, which showed especially remarkable change, can be used for determing the chemical dose of the ray below hundreds of roentgen.