244 PATHOLOGICAL VARIATIONS OF THE PERCUSSION SOUNDS. 



separated from the chest-wall by the thin anterior margins of the lung, 

 percussion gives a muffled sound, while further outwards a clear lung 

 percussion sound is obtained. During deep inspiration, the inner 

 margin of the left lung reaches over the heart as far as the insertion 

 of the mediastinum, whereby the dull sound is limited to the smallest 

 triangle, t, i, i'. Conversely, during very complete expiration, the 

 margin of the lung recedes so far that the cardiac dulness embraces 

 the space, t, e, e. 



115. Pathological Variations of the Percussion 



Sounds. 



The normal clear resonant percussion sound of the lungs becomes muffled when 

 infiltration takes place into the lungs, so as to dimmish the normal amount of air 

 within them, or when the lungs are compressed from without, e.g., by effusion of 

 fluid into the pleura. The percussion sound becomes clearer when the chest-wall 

 is very thin, as in spare individuals during very deep inspiration, and especially 

 in emphysema, where the air-vesicles of certain parts of the lung (apices and 

 margins) become greatly dilated. 



The pitch of the percussion sound ought also to be noted. It depends upon the 

 greater or less tension of the elastic pulmonary tissue, and on the elasticity of the 

 thoracic wall. The tension of the elastic tissue is increased during inspiration and 

 diminished during expiration, so that even under physiological conditions, the 

 pitch of the sound varies. 



The sound is said to be tympanitic (Skoda) when it has a musical quality 

 resembling the timbre of a sound produced on a drum, and when it has a slight 

 variation in pitch. If a caoutchouc ball be placed near the ear, on tapping it 

 gently, a well-marked tympanitic sound is heard, and the sound is of higher pitch 

 the smaller the diameter of the ball. A tympanitic sound is always produced 

 on tapping the trachea in the neck. A tympanitic sound produced over the 

 chest is always indicative of a diseased condition. It occurs in cases of cavities 

 or vomicse within the substance of the lung (the sound becomes deeper when the 

 mouth, or, better, the mouth and nose, are closed), when air is present in one 

 pleural cavity, as well as in conditions where the tension of the pulmonary tissues 

 is diminished. The tympanitic sound resembles the metallic tinkling which is 

 heard in large pathological cavities in the lungs, or which occurs when the pleural 

 cavity contains air, and when the conditions which permit a more uniform reflec- 

 tion of the sound-waves within the cavity are present. 



When percussing a chest, we may determine whether the substance lying under 

 the portion of the chest under examination presents great or small resistance to 

 the blow, either of the percussion-hammer or of the tips of the fingers, as the case 

 may be. 



Phonometry. If the stem of a vibrating tuning-fork be placed on the chest- 

 wall over a part containing air, its sound is intensified ; but if it be placed over a 

 portion of the lung which contains little or no air its sound is enfeebled (von 

 Baas). 



Historical. The actual discoverer of the art of percussion was Auenbrugger 

 (t!809). Piorry and Skoda developed the art and theory of percussion, while 

 Skoda originated and developed the physical theory (1839). 



