As a preliminary step to furnish date for determining the MAC value of acetone, some biological reactions were checked on subjects who under went "one-day exposure", i.e. exposures in the morning and afternoon for three hours each in a day, to acetone. Twenty-five healthy male students about 22 years old were selected as the subjects, being divided into 5 groups. Four groups were exposed to 1000, 500, 250 and 100 ppm acetone respectively for 6 hours with 45 minutes' intermission in the middle, the remaining group being the control. Responses of the subjects to acetone were observed for 56 hours after the beginning of the exposure. 1) Subjective symptoms Odor of acetone was more or less recognized by all the exposed groups, but while the exposure lasted the subjects seemed to get used to the sense of smell. Irritation on the mucous membranes was recognized by most of the 1000 and 500 ppm groups, but only a few recognized it in other groups. The organs on which the subjects recognized irritation most were nose, and then eyes, throat and trachea in the decreasing order. Chiefly in the 1000 and 500 ppm groups, some complaints of a physical disorder were noted in the following morning. These complaints were a feeling of tentin, general weakness, heavy eyes, lacking in energy, etc. In the 250 ppm group persons corresponding to about half the complainants in the 500 ppm group in number complained the above symproms, whereas almost none in the 100 ppm group made a complaint. 2) Acetone concentration in the blood and urine In the 1000, 500 and 250 ppm groups, acetone concentration in the blood had obviously increased since the beginning of the exposure, and it reached the maximum value in 7 hours, i.e. 15 minutes after the exposure was completed. It decreased to the ordinary value in 48 hours, i.e. in the morning after next, in the 1000 ppm group, in 32 hours in the 500 ppm, and 24 hours in the 250 ppm. There is a certain correlation between the acetone concentration in the blood and that in the air in each group, but not a direct proportion. Almost the same changes were noted in acetone concentration in the urine. 3) Behavior of leucocytes Leucocyte counts of the peripheral circulating blood increased after the beginning of the exposure more than the daily fluctuation in the 1000 and 500 ppm groups, but in the other groups they did not so much. In the classification of leucocytes no distinctive signs were noted even in the two former groups. Circulating eosinophil counts increased in the 1000 and 500 ppm groups in contrast with the daily fluctuations of the other two exposure groups and the control. They decreased to the ordinary value in 32 hours. Phagocytic activity of neutrophils reduced after the beginning of the exposure in the 1000 and 500 ppm groups, recovering to the previous value in 48 hours. A slight decline of phagocytic activity was observed in the 250 ppm group, but not in the 100 ppm group. 4) Other findings in the urine Some abnormal signs were found in the reaction of urobilinogen in the urine in the 1000 ppm group, but not in the other groups. The findings were obtained in the evenings of the day of the exposure, i.e. 7 hours after the beginning of the exposure, and of the next day, i.e. 32 hours after. Regarding urinary protein and hemoglobin content, no distinctive features were found in any group. As stated above, some significant signs were observed even in the 500 ppm group under the conditions of our experiments. Therefore, it seems that the MAC value of acetone of 500 ppm, determined by the Japan Association of Industrial Health, must undergo further consideration.
