Blood alcohol and impairment of judgment.

1. The cerebral depressant effect of 30 ml of aqueous ethanol diluted to 25% and administered orally to 16 volunteer subjects was compared with a control group of 15 volunteer subjects. 2. The two parallel forms of the Watson--Glaser Critical Thinking Appraisal tests were employed as a measure of cerebral function. 3. The control group showed a small but statistically insignificant improvement on retesting with Watson--Glaser test form ZM after preliminary administration of form YM. 4. The relationship between the blood alcohol time curve and the alcohol effect was analysed for each individual subject, each subject being used as his own control. 5. The main peak cerebral depressant effect was substantial and occurred on average 25.5 min before the attainment of the peak blood alcohol concentration. 6. There was no significant correlation between blood alcohol concentration and contemporaneous cerebral impairment (r = -0.01). 7. There was a highly significant correlation (r = 0.60) between the effect upon cerebral function and the gradient of the blood alcohol curve at that time.