Following the previous studies, similar biological reactions were checked on subjects exposed for longer days for the purpose of determining the MAC value of acetone. Male students 22 years old or thereabouts were exposed to acetone for 6 days, 6 hours a day, in the exposing chamber made by us for men, and were examined for 10 days since the beginning of the exposure. Acetone concentration in the air were set at 500 and 250 ppm respectively for different groups of six members each. On the 250 ppm and the control groups a working load of about 2 in the relative metabolic rate was imposed in separate experiments besides those without such load. The items and the methods of the experiments were selected according to the results of the previous studies. 1. Subjective symptoms were almost the same as those of the "one-day exposure". The complaints, e.g. objectionable odor and irritation on the mucous membrane during the exposure, and various physical disorders, which lasted until the next morning, were remarkable in the 500 ppm group but slight in the 250 ppm group irrespective of the working load. 2. Acetone concentration in the blood and the urine increased rapidly during the exposure. In the 250 ppm group it decreased to the ordinaty value in the next morning notwithstanding the working load, but in the 500 ppm group it remained fairly high at least 48 hours after the exposure. Moreover, in the 500 ppm group the course of the acetone concentrations revealed a characteristic trend with the lapse of days of the exposure. 3. Leucocyte counts of the peripheral circulating blood increased, phagocytic activity of neutrophils decreased, and eosinophil counts increased in the 500 ppm group. In the 250 ppm group almost the same results were obtained, though slight, irrespective of the working load. The difference between the 250 ppm groub and control was not statistically significant. 4. The simple reaction time showed a clear difference between the exposure groups and the control. In the 250 ppm group, the reaction time was found to delay as compared with that of the control at an early stage of the exposure, but it became nealy the same afterwards. In the 500 ppm group, though similarly the delay was noted during the exposure, the reaction time was even shorter than that of the contral during the recovery period. From the above results and those appearing in the literatures, we think that the present MAC value of 500 ppm, determined by the Japan Association of Industrial Health, is questionable, and that it is preferable to lower it tentatively to some 200 ppm.

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To search for a good medical care system for gastric and duodenal diseases in industry, mass screening examination system and out-patient clinic system were compared in terms of efficiencies for finding workers to be cared medically or to be kept under medical surveillance. Percentage of workers who needed further medical care among the total screenees was higher in the out-patient clinic system han in the mass screening system. The difference in the percentage of case-finding was most distinct in cases of gastric ulcers and scars, and was not so distinct in those of duodenal ulcers. Number of cases of interruption for, medical care after screening amounted to one fifth of the total number concerned in the both systems. From these facts the necessity of enforcement of health education program was discussed.

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