Physical diagnosis, including diseases of the thoracic and abdominal organs : a manual for students and physicians .. . ed to the underlying lung,and a clear, well-defined pulmonary resonance is ob-tained, scarcely modified by the sound given off by thebony thorax. Percussion in children should thereforebe light, otherwise diffuse vibrations are set up and reso-nance is obtained from a large extent of lung tissue. As the bones of the thorax become more rigid, espe-cially in old age, the bony sound becomes more markedand there is a raising of pitch, so that it is described asa boardy or wooden
Physical diagnosis, including diseases of the thoracic and abdominal organs : a manual for students and physicians .. . ed to the underlying lung,and a clear, well-defined pulmonary resonance is ob-tained, scarcely modified by the sound given off by thebony thorax. Percussion in children should thereforebe light, otherwise diffuse vibrations are set up and reso-nance is obtained from a large extent of lung tissue. As the bones of the thorax become more rigid, espe-cially in old age, the bony sound becomes more markedand there is a raising of pitch, so that it is described asa boardy or wooden note. (3) Influence of the Pleura.—The normal pleura haspractically no effect on the vibrations produced by per-cussion, but pathological changes which canse thickeninginfluence them in a marked degree. 88 TEE RESPIRATORY SYSTEM. On account of the close relation that the pleura bearsto the ribs a very slight thickening is sufficient to inter-fere with the vibrations that are set up by percussion ofthe overlying structures. This is detected not only irthe sound elicited, but in a peculiar hard feeling im- Fig. 27. 1 and 2 show effect of weak percussion over pleurae. 3 and 4 showeffect of strong percussion over pleurae. PERCUSSION. 89 parted to the fingers. The ordinary springy condition ischanged to one of increased resistance and varies in de-gree accord in; to the character of the changes in thepleura. When the thickening is caused by now tissue homo-geneous with the pleura, then its influence is slight. Ifa thick layer of plastic exudation covers the surface thenthe dullness will be in direct proportion to its thickness: A collection of fluid within the sac renders the noteflat, the feeling being similar to that noticed when thethigh is struck. In order to determine whether or not the variation inthe resonance is due to pleuritic thickening or to changesin the pulmonary tissue, the effect of percussion ofdifferent degrees of force must be used. Light percussion will be mark
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