28 CLINICAL DIAGXOSTICS 



normal lung when the chest walls are covered with heavy 

 muscles, fat, or edematous swellings. 



The sound is comparatively dulled when air-containing 

 parts of limited dimensions are percussed (borders of the lung, 

 and under thick thoracic wall) or if small airless spaces lie 

 amid those containing air (nodular thickenings in the lung). 



During the application of percussion we should note the 

 resistance the part offers to the hammer or striking finger. 

 [To understand what is meant by this the student should 

 strike with the plexor some solid object, as a brick wall, and 

 compare it with the feeling experienced when the human chest 

 is percussed]. By placing the index finger on the back of the 

 hammer the resistance can be better appreciated. From the 

 resistance the amount of vibration that can be induced in the 

 underlying parts may be determined, the greater the former 

 the less developed the latter. For this reason solid, airless 

 parts like muscle give a shallow percussion-sound and causes 

 the hammer to suffer a jar when they are struck. 



Tactile Percussion. 



The combination of palpation and percussion is called 

 tactile percussion. Through this method we endeavor to ar- 

 rive at the physical condition of deep-lying parts by stroking 

 the tissues covering them. 



METHOD. The wrist and fingers should be held slightly 

 flexed and fixed. The parts to be examined should be pressed 

 firmly with the finger tips, exerting an interrupted stroke. 

 After such a stroke the fingers should be allowed to dwell for 

 a moment to note the recoil of the under-lying tissue the con- 

 sistency of which we wish to determine. In practicing this 

 form of percussion bear in mind that the deeper rather than 

 the shallower tissues are to be felt. 



Tactile percussion may also be practiced with the plexor 

 and pleximeter, the index finger being rested upon the back 



