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The pinnae of white mice, when exposed to high intensity airborne sound waves, exhibit an immediate inflammation followed by degeneration. Treated pinnae were compared histologically with normal pinnae, with pinnae treated with high temperatures, and with pinnae of mice which were depilated around the ears and treated with sound so that no heat could be produced by absorption of sound in the fur. The results showed that the major factor in destruction of the pinnae is heating in the fur, but some of the effects produced by sound are probably the results of mechanical agitation or a combination of heating and mechanical agitation.