126 INIANUAL OF EQUINE MEDICINE. 



in close contact with the walls, a fairly resonant note is 

 heard in health, the sound depending on the vibration of 

 the air in the pulmonary tissue, and on the vibration of the 

 chest-walls themselves. 



General increase of resonance occurs in the chest in cases 

 of pulmonary emphysema. Partial increase may occur 

 over areas where the lung has become more functionally 

 active, and dilated in consequence, ■ from loss or impaired 

 function of the rest. Diminished resonance may occur 

 from any cause obstructing the entrance of air into the 

 vesicles of the lung. Loss of resonance may be due to 

 hepatization of the lung or to effusion into the pleural 

 cavity. 



AUSCULTATION. — By auscultation we mean listening 

 to the sounds of the interior, either directly, by application 

 of the ear to the surface, or indirectly, by means of a stetho- 

 scope. In the normal condition, auscultation of the 

 respiratory organs of the horse reveals at least three 

 typical sounds : 



1. Tracheal, Laryngeal or Nasal Breathing. 



This may be heard over the larger cavities of the head, 

 the larynx, and the trachea. 



It is a soft blowing murmur, audible during inspiration 

 and expiration, between which there is a short interval. 



2. Bronchial or Tubal Breathing. — This breathing is 

 harsher, and of shorter duration and less intensity, than the 

 tracheal. The interval, also, between inspiration and ex- 

 piration, is less marked. It is best heard at the bifurcation 

 of the trachea, at the anterior part of the chest. 



Over the superior and middle third of the chest it is less 

 characteristic, and is most distinct in the upper third. 



3. Pulmonary or Vesicular Breathing, or Respiratory 

 Murmur. — The respiratory murmur is due to the entrance 

 of air into the vesicles, or to conduction of the laryngeal 



