432 DISEASES OF THE llESl'IRATORY ORGANS. 



air-tube. By either mediate or immediate auscultation the 

 sound conveyed to the ear over the greater portion of these 

 different sections of the great air-tube during rest is wonder- 

 fully alike, consisting of a slight murmur of a soft character, 

 of equal intensity and pitch on both sides of the face, audible 

 during both inspiration and exjDiration, there being an appreci- 

 able interval betvveen these parts of the respiratory act, the 

 latter probably the higher pitched and longer continued. At 

 the inferior portion of the trachea a slight modification of the 

 sound is heard, known as the ' tracheo-bronchial ' sound or 

 respiration, caused by the passage of the air to and from the 

 bronchi; it is most distinct during expiration, and augmented 

 by exertion. 



2. Bronchial or Tubal. — This sound is heard in its purity as 

 the tracheo-bronchial respiration referred to as existing at 

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

 As detected over the superior and middle third of the chest it 

 is less characteristic, and in health is apt to be mixed up with 

 the vesicular sound ; in disease there is much less danger of 

 this. 



In character it is harsher, not so loud, and of shorter dura- 

 tion and intensity than the tracheal; while the interval 

 between the inspiratory and expiratory acts, although still 

 appreciable, is less marked. 



These tubal sounds are most distinct in the upper third of 

 the chest, least so at the superior part of the lower third where 

 the vesicular sound is loudest. The nearer we get to the root 

 of the lungs, and the divisions of the bronchi, the better is 

 this sound recognised. 



3. Pulmonic or Vesicular. — This sound, otherwise known as 

 the respiratory murmur, is the impression of disturbance con- 

 veyed to the ear in the act of auscultation during both inspira- 

 tion and expiration, between which no interval is appreciable. 

 It may be heard when the horse is at rest, particularly if the 

 walls of the chest are not heavily clad with muscular tissue or 

 loaded with fat, and is intensified by exertion or whatever 

 tends to accelerate the respiration. It is believed to be the 

 result of the entrance into and exit from the air-sacs of the 

 respired air, together with the dilatation of these, and the 

 pecuharity of their form in relation to the terminal bronchi. 



