Aiisailtation. 171 



dry, thickened and inelastic. 2d. When that portion of lung in- 

 tervening between one of the larger tubes and the surface of the 

 chest is solid (hepatised) and thus proves a better conductor of 

 sound than in the normal condition. 



Superadded abnormal sounds. The bronchial sounds may 

 be altered in their character so as to become cavernous, am- 

 phoric or mucous (ratthng). The cavernous sound is usually 

 caused by the presence in the lung of the cavity left after the 

 discharge of an abscess or softened tubercle into a bronchial 

 tube. It is thus preceded by cough and white, creamy discharge 

 from the nose. If the discharge is fetid and grumous there has 

 probably been circumscribed gangrene of the lung. An approxi- 

 mation to the sound may be produced by blowing into a wide- 

 mouthed glass or porcelain vessel. The sound of amphoric 

 respiration on the contrary is like that made.by blowing into a 

 narrow-necked bottle. It is due to a similar cavity with a small 

 orifice or to the existence of pneumo-thorax communicating by a 

 narrow canal with a bronchial tube. It is rare in the lower ani- 

 mals, but Delafond mentions one case in the horse and two in 

 dogs. 



Rales. The remaining morbid sounds are known as rciIes, or 

 rattles. They may either be referable to the bronchial tubes or 

 the lung tissue. They are called dry or humid, according as 

 they convey the idea of air drawn through a dry tube or one 

 containing liquid. 



The dry rales are due to narrowing of the bronchial tubes 

 from the pressure of adjacent tumors, the thickening of the 

 mucous membrane or the deposition on the surface of layers 

 of tenacious mucus. The greater the narrowing the shriller the 

 sound, and hence the distinction of bronchial rales into sonorous 

 and sibilant (whistling). 



The sonorous rale has been variously exemplified by the hum- 

 ming of a gnat, the cooing of a wood pigeon or the bass notes of 

 a violin. It commonly bespeaks the onset of bronchitis and tes- 

 tifies to the thickened, dry and rigid character of the tubes, but 

 may give place in as short a time as three hours to a mucous rale 

 from the occurrence of a free secretion. It rarely extends over 

 two or three days. Sometimes when caused by a piece of tena- 

 cious mucus obstructing a tube, it is very transient disappearing 



