According to their effects on man, the author distinguishes between four different noise zones, the transition to the next zone being characterised by the appearance of an additional effect. These are: psychic reactions, vege tative reactions, injuries to the internal ear, and, finally, mechanical de struction of ganglion ceIls. The author gives examples of psychic reactions, depending not only on the nature of the noise but also on the mental attitude of the person per ceiving the noise towards its source. The most characteristic re action is a constriction of peripheral blood vessels,...