RESPIRATORY APPARATUS. 117 



the horse is usually held in the position of "middle inspiration " 

 It IS necessary to induce forced inspiration and expiration To 

 do this the thorax is encircled with a girth which is slowly 

 and gently drawn tight and relaxed, alternately, imitating 

 forced breathing. The larynx in the meantime is watched 

 through the mstrument. At each inspiration the healthy car- 

 tilage IS seen to move outwardly, while at each expiration it 

 approaches the middle line. The diseased cartilage, on the 

 other hand, either remains completely at rest (paralysis) or its 

 movements are very tardily performed (paresis). 



In bilateral paralysis (paraplegia) of the larynx the 

 patient may show dyspnea when at rest— at any rate, slight 

 excitement will induce it. In such cases one will note that 

 both arytenoids protrude into the lumen of the larynx at inspi- 

 ration ; at expiration they are suddenly forced laterally and set 

 in vibration. The paralysis can be complete or incomplete; 

 It may not be developed to the same degree on both sides. 



Palpation. When we determine the seat of the en- 

 largements by palpation we ma^ at the same time note 

 their temperature, sensitiveness, and the ease with which 

 cough can be induced by pressing upon them. Where much 

 exudation is found in the larynx, infiltration of the vocal cords 

 or other folds of mucous membrane, a trembling of the organ 

 may be felt {laryngeal fremitus). 



In examining the trachea we should look out for scars 

 resulting from tracheotomy wounds. The 

 form of the trachea should also be noted. In chronic trachei- 

 tis of the ox the trachea may be shaped like a saber scabbard. 

 Flattening of the trachea in horses is probably due to a 

 paralysis of the transverse muscle. 



On auscultation of the larynx or trachea, nor- 

 mally a stenotic sound is heard [Hke a German "ch"]. It is 

 due to a vibration of the vocal cords and laryngeal walls which 

 is produced by the air forced through the organ. It is heard 

 best at expiration. When the mucous membrane of the lar- 

 ynx is swollen and firm, this sound becomes very pronounced 



