Leopold Auenbrugger (1722-1809) discovered the diagnostic value of percussion in Vienna in 1781. He tapped the chest or another body part and listened to the resonant quality of the sounds. When a healthy patient’s chest is tapped it produces a hollow sound. Fluid congestion or certain diseases alter the sound to a dull, flat thud. This is an example of a combined pleximeter and percussor. It was developed by Francis Sibson (1814-1876) in the 1850s. The ivory pleximeter was held on the skin. It was tapped with the hammer-like rubber-tipped percussor suspended within the instrument. The belief was this gave clearer sounds than using the fingers.