The experimental evidence that tends to establish the position of alcohol as an inhibitor and disturber rather than a promoter of mental activity has been gathered largely by German investigators. Many of their experiments are of a rather technical character, aiming to test the basal operations of the mind. Others, however, are eminently practical, as we shall see. The earliest experiments, made by Exner in Vienna so long ago as 1873, aimed to determine the effect of alcohol upon the so-called reaction-time. The subject of the experiment sits at a table, with his finger upon a telegraph key. At a given signal--say a flash of light--he releases the key. The time that elapses between signal and response--measured electrically in fractions of a second--is called the simple or direct reaction-time. This varies for different individuals, but is relatively constant, under given conditions, for the same individual. Exner found, however, that when an individual had imbibed a small quantity of alcohol, his reaction-time was lengthened, though the subject believed himself to be responding more promptly than before. These highly suggestive experiments attracted no very great amount of attention at the time. Some years later, however, they were repeated by several investigators, including Dietl, Vintschgau, and in particular Kraepelin and his pupils. It was then discovered that, in the case of a robust young man, if the quantity of alcohol ingested was very small, and the tests were made immediately, the direct reaction-time was not lengthened, but appreciably shortened instead. If, however, the quantity of alcohol was increased, or if the experiments were made at a considerable interval of time after its ingestion, the reaction-time fell below the normal, as in Exner's experiments.