According to their effects on man, the author distinguishes between four
different noise zones, the transition ta the next zone being
characterised by the appearance of an additional effect. These are:
psychic reactions, vege- tative reactions, injuries ta the internal ear,
and, finally, mechanical de- struction of ganglion cells. The author
gives examples of psychic reactions, depending not only an the nature of
the noise but also an the mental attitude of the person per- ceiving the
noise towards its source. The most characteristic reaction is a
constriction of peripheral blood vessels, followed by a decrease in
circula- tion in the whole body. The degree of this reaction depends an
the intensity of the noise, but not an its frequency, though the width
of the noi se band plays an important r8le. As ta the vegetative
reactions, there is no adaptation to noise. In sleep they are stronger
than in a wakeful state. Exposure ta noise for years causes persistent
effects an the blood flow through the skin, but also an the heart action
and the regulation of the equilibrium. Noise of more than 90 phones may
prove injurious ta the auditory ap- paratus. Higher frequencies are more
detrimental than lower ones. The audiometric diagram allows ta
distinguish between traumatic injuries and those due ta old age.
Extraaural effects of noise are only ta be found among operators of jets
and rockets, especially at test-stands, and may be pre- vented by
wearing protective devices.