26 



CLIXICAL DIAGXOSTICS. 



The Qualities of Percussion-Sounds. 



A body can only then produce a sound when it has lost 

 its equilibrium and vibrates by virtue of its elasticitv. Two 

 principles form the basis of percussion : 



1. Solid, airless parts of the body give forth a flat sound 

 of short duration and little intensity. Such a sound is called 

 dull, femoral or empty. 



Fig. 2. Fig. 3. Fig. 4. 



2. If an air-containing organ is set in vibration it pro- 

 duces a sound of considerable intensity, duration and tone, 

 the so-called resonant sound. 



The clearness of the sound depends upon the volume of 

 the air-containing organ which is vibrating. 



a. The stronger the percussion the larger is the part 

 which vibrates and the fuller the sound (Fig. 2). 



b. The thinner the over-lying tissue of the thoracic wall 

 the more lung tissue will vibrate and the fuller the sound 

 (Fig. 3). 



c. If the volume of the air-containing organ is small in 

 itself then the sound is correspondingly less intensive (Fig. 4). 



This explains the varying intensity of the sound over dif- 

 ferent portions of the chest wall when the percussion blows 

 are applied with equal force. The resonant sound gradually 

 merges into the dull femoral as we approach the forward and 

 upper portions. 



