THE NORMAL RESPIRATORY SOUNDS. 221 



as when the pleural cavity contains air, when the conditions are suitable for a more 

 uniform reflection of the sound-waves within the cavity. When a percussion- 

 stroke is made over cavities, especially in the upper anterior part of the lung, 

 the air at times escapes with a peculiar ringing and hissing sound the cracked- 

 pot sound (or coin-sound). 



In practising percussion it should be observed by the sense of touch whether 

 the underlying parts offer a feeling of greater or lesser resistance to the stroke ; and 

 at the same time the vibratory power may be noted. Under normal conditions 

 small vibratory power is associated with a well-developed bony framework, thick 

 soft parts, and tense muscles. Pathologically, lessened vibration always occurs in 

 connection with an airless condition of the lungs, and is associated with a dull 

 percussion-note. Diminution of the resistance to the percussion-stroke is found 

 normally in slender chests. Pathologically, it occurs when there is a considerable 

 amount of air under the chest-wall, hence in the presence of pneumothorax and 

 of abnormal expansion of the lungs by means of air. 



If the handle of a tuning-fork be placed upon the chest-wall, the fork will 

 sound loud over spaces rilled with air, and will yield a weak note over spaces 

 containing little or no air (Baas' phonometry). 



THE NORMAL RESPIRATORY SOUNDS. 



By listening over the chest- wall, either directly or by means of a 

 stethoscope, the vesicular murmur can be heard during inspiration, 

 wherever the lungs are in contact with the walls of the thorax. The 

 character of this sound can be imitated if the mouth be placed in the 

 position necessary for the act of sipping, and a sound between f and v 

 be softly emitted. The sound is a sipping, rustling, hissing one. It 

 is due to the sudden expansion of the pulmonary vesicles by the entrance 

 of inspired air (hence the term vesicular) and also to the friction of the 

 air passing through the alveoli. The sound is at times softer, at times 

 louder. It is constantly louder in children under the age of twelve 

 years, as the air- vesicles are one-third narrower than in adults, and 

 cause greater friction with the entering air. 



During expiration the air, when leaving the vesicles, gives rise to a 

 weak puffing sound of an uncertain soft character. 



The cardiopulmonary murmur heard in the vicinity of the heart when the 

 latter contracts during systole likewise has a vesicular character. 



Bronchial breathing may be heard in the larger air-passages during 

 inspiration and expiration, and resembles the sound of a loud, sharp h 

 or sh. Outside of the neck (larynx and trachea) it may be heard be- 

 tween the shoulder-blades at the level of the fourth dorsal vertebra 

 (point of bifurcation), especially during expiration. It is somewhat 

 louder to the right, on account of the larger caliber of the right bronchus. 

 In all other parts of the thorax it is obscured by the vesicular murmur. 

 The bronchial breathing arises entirely in the larynx, from the forma- 

 tion of air- vortices, by reason of the marked constriction of the air- 

 passage at the glottis. This laryngeal stenosis-sound causes a resonance 

 of the tracheo-bronchial air-column, and thus produces the specific 

 character of bronchial breathing, which the listener hears transmitted 

 along the large tubes of the bronchial tree. 



It has been maintained that, if the air-filled lungs of an animal be applied 

 to the neck over the larynx or trachea, the bronchial breathing produced there 

 will become vesicular. In that case it must be supposed that vesicular respiration 

 arises from a weakening and acoustic transformation of tubular respiration by r 

 transference through the air- vesicles. Added to this is the fact that it is impos 

 to produce any sound by forcibly driving air through narrow straws. 



