CROUPOUS PNEUMONIA. 185 



contact with the side of the chest but only in such a case the percus- 

 sion-sound is deadened, and during the act of percussion an increase of 

 resistance is felt over the point struck. This is because a hepatized 

 *ung, like any other compact body void of air, cannot be made to 

 vibrate. The thicker and wider the hepatized region lying in contact 

 with the chest, so much the more marked are the dulness and resist- 

 ance. When the dulness is but slight, it will generally be perceived 

 that the sound is also hollow ; when the sound is perfectly dull, the full 

 and hollow tones cannot be appreciated. When the seat of the dis- 

 ease is central, that is to say, at the roots of the lung, very extensive 

 hepatization of the lung may exist without alteration of the sound upon 

 percussion. 



Auscultation during the stage of engorgement usually affords a 

 crackling sound to the ear, like that which is heard when one throws 

 salt into the fire, or when a few hairs are rubbed between the fingers 

 before the ear. This crackling (Laennec's rdle crepitant), which is 

 formed in the minute spaces of the bronchial terminations and pul- 

 monary vesicles, is the finest of all the moist rdles, and, as the fluid in 

 which it arises is extremely viscid, it is also the dryest of the moist rales. 

 Then* mode of origin perhaps is, that the vesicular walls, which during 

 expiration became glued together, are forcibly separated by the air 

 which enters upon inspiration. As soon as that portion of the lung 

 which touches the thoracic wall is completely infiltrated, vesicular breath- 

 ing is arrested, as the vesicles there are impenetrable to the air. In- 

 stead bronchial respiration is heard, that is to say, we hear the sound 

 which the to-and-fro movement of the air in the trachea and larger bron- 

 chi is always making, but which is not transmitted to the ear through 

 the healthy lung, the structure of which, consisting of alternations of 

 air and vesicular wall, furnishes a poor conducting medium. When, 

 instead of this bad conductor of sound, a uniform medium lies between 

 the ear and the bronchi, these bronchial sounds become audible ; always 

 provided, that the bronchi communicate with the trachea, so that the 

 air may either pass to and fro in them, or that the air which they already 

 contain may be set in vibration with every breath. Moreover, the bron- 

 chi in the condensed part of the lung form better conductors of sound 

 than those which traverse the normal lung. If the bronchi should be 

 filled up by accumulated secretion, as often happens temporarily in the 

 third stage of pneumonia, the bronchial breathing ceases, and does not 

 again become audible until the bronchi have become emptied by 

 coughing. 



Bronchophony arises under conditions similar to those under which 

 bronchial respiration is produced. The vibrations of the vocal chords 

 iuring speech are conducted along the column of air in the larger bron- 





