AUSCULTATION. 519 



monary tissue, which thereby becomes a better conductor of 

 sound, and enables us to hear the sound of bronchi over a 

 greater extent of surface. 



Diminution, like augmentation, of the sound may be partial 

 or general. Partial diminution commonly results from pul- 

 monary congestion, is accompanied by a supplementary mur- 

 mur in other parts of the lung, and is succeeded by the 

 humid crepitant rale, which announces the onset of inflamma- 

 tion. It is likewise an accompaniment of emphysema in 

 which air readily enters the dilated air sacs, or adventitk^is 

 vesicles, but cannot be expelled in consequence of the lung 

 tissue having lost its elasticity. 



General diminution of the murmur may depend on nu- 

 merous causes, and frequently such as do not directly impair 

 the thoracic viscera. Thus it may depend on certain diseases 

 of the brain causing sluggish respiration. Ansemia or low 

 fevers may, by their prostrating influence, lead to a similar 

 result. The same remark applies to enteritis, peritonitis, or 

 any violent abdominal pain which renders the breathing slow 

 and careful. Obstructions in the glottis or trachea may act 

 in a similar way. Percussion will enable the practitioner to 

 ascertain the healthy condition of the lung in these various 

 cases. The cause may, however, reside within the thorax, as 

 tuberculosis with calcareous deposition, catarrhal bronchitis 

 with an abundant secretion which blocks up the greater part 

 of the small bronchial tubes, or general emphysema, in which 

 the lung has lost its elasticity. In the case of the last lesion 

 there is generally consistent bronchitis, and percussion detects 

 an abnormal resonance. 



Various other modifications of the respiratory murmur are 

 occasionally met with. Thus the sound may be absent at the 

 commencement of respiration, but appears towards its con- 

 clusion; this seems to result from some obstruction, as mucous 



