A uscultation . 173 



the sound has been attributed to the passage of air through the 

 thick mucus in the smallest bronchial tubes or more plausibly to 

 the separation of the walls of the air sacs and cells during inspir- 

 ation, they having been previously adherent by reason of the se- 

 cretions. 



Crepitation is not heard in all pulmonary inflammations. In 

 weak animals with a low type of inflammation tending to gangrene, 

 and in those cases of broncho-pneumonia in which a viscid mucus 

 blocks up the bronchial tubes passing to the affected lobes, it may 

 \>t altogether absent. 



Crepitation may further occur without inflammation. Thus in 

 pulmonary oedema (dropsy of the lung) and capillary hemorrhage 

 in which liquids are effused in the smaller bronchial tubes and air 

 sacs a crepitation is sometimes heard. 



A niDdified crepitation (dry crepitant rale of Delafond) is 

 usually heard over an emphysematous lung. The noise in this 

 cas^ has been compared to that induced by handling a sheet of 

 paper. 



The subcrepitant rile is another modification holding a place 

 intermediate between the crepitant and the mucous rales. It has 

 been likened to the sound of a moderate effervesence in beer or other 

 liquid. It is referable to the presence of mucus in the smaller 

 bronchial tubes and indicates bronchitis or broncho-pneumonia. 



Still other sounds are heard in diseased conditions of the pleurae. 

 These are friction sound, creaking, metallic tinkling, and 

 gurgling or splashing. 



A friction sound is heard in the early stages of pleurisy and is 

 caused by the dryness of the pleural surfaces from the absence of 

 the halitus or vapor which normally moistens them and the depo- 

 sition of layers of lymph by which the surfaces are rendered rough 

 and uneven. An approximate sound may be observed by placing 

 the palm of the left hand on the right ear and drawing a finger 

 of the right softly over its back. The sound is quick and jerking, 

 one or a few jerks only being heard with each inspiration as the 

 act is cut short on account of the pain attending the friction. It 

 is rarely heard in expiration. It is chiefly heard at the lowest 

 part of the chest where the lungs have the greatest freedom of 

 movement. The thinness of the walls of the chest above the breast 

 bone in cattle and dogs permits the friction sound to be heard more 



