PHYSICAL SIGXS DRAWX FROM AUSCULTATIOX. 433 



There arc doubts, however, that this exphination is wholly 

 coiTect, some considering that, hke the tubal, the vesicular 

 sound may originate in the larynx, and as heard over the chest, 

 is the result of conduction and modification. 



The character of the sound is that of a soft diffuse murmur, 

 and has been compared to the rustling of a gentle breeze 

 amongst green leaves ; it is better detected, as well as more pro- 

 longed, during inspiration; in expiration it is when heard — which 

 is not always possible — more readily accomplished, and feebler, 

 without the diffuse breezy character. It is heard in its purity 

 at a distance from the greater air-tubes, and Avhere the paren- 

 chyma of the lungs is most abundant. The characters of this 

 sound are, in health, subject to variations which require to be 

 noted that they may not be confounded with disease. It is 

 most distinct in well-bred horses with deep rather than round 

 chests, and where the walls of the cavity are not loaded with 

 soft tissue, also when the animal's stomach and intestines are 

 not distended with food, by which, through pressure on the 

 diaphragm, the thoracic cavity is confined. 



It is louder or stronger in the young than in aged animals, 

 from the air-cells being more numerous and smaller, and the 

 entire pulmonary tissue being more elastic in nature; this 

 condition of 'juvenile' respiration gradually, with years, gives 

 place probably to a dilatation of air-sacs and weakening of 

 lung-tissue, until the so-called ' senile ' respiration is estab- 

 Hshed. 



In the horse this murmur is distinctly enough heard over the 

 greater portion of the chest — about two thirds — which is 

 exposed for auscultation. 



Over both sides of the chest it may be detected fi-om behind 

 the scapuhe, or elbows, slightly increasing in force to the tenth 

 or twelfth rib, thence becoming diminished. On the left 

 side in the lower third the pulsations of the heart interfere with 

 its detection. 



B. Changes in the Health Sounds over the Respiratory Tract due 

 to Disease. 1. Anterior Air Passages. — In such conditions as 

 engorgement of the pituitary membrane, or where adventi- 

 tious growths occupy the air-cavities of the head, a more or less 

 blowing or interrupted sound is given out. When the obstruc- 

 tion is very considerable, cither from morbid growths or general 



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