Leopold Auenbrugger (1722-1809) discovered the diagnostic value of percusion in Vienna in 1781, tapping the chest or another body part and listening to the resonant quality of the sounds. When a healthy patient's chest is tapped it produces a hollow sound, but fluid congestion or certain diseases alter the sound to a dull, flat thud. The pleximeter was held on the skin, and tapped with the hammer (percusor), such as this example which has a wooden handle and a rubber tipped metal head. It was believed that this gave clearer sounds than just using the fingers. The pleximeter shown has an ivory plate bearing a measuring scale.
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