122 PRACTICE OP EQUINE MEDICINE. 



What is understood by the term "roaring"? 



It is a symptom of a diseased condition of part of tlie respira- 

 tory tract, cliaracterized by an abnormal sound heard during tlie 

 act of respiration, and at a variable distance from the patient. 



Give the causes. 



In the majority of cases it is caused by an atrophy and a 

 degeneration of the dilator muscles of the glottis — the posterior 

 crico-arytenoid muscles. All these muscles are innervated by the 

 inferior laryngeal nerve, which is a branch of the pneumogastric. 

 One of these nerves often loses its influence, becoming paralyzed 

 and undergoing fatty degeneration. 



The left recurrent laryngeal nerve runs through a bunch of 

 lymphatic glands, which often become enlarged and press on the 

 nerve. The left recurrent laryngeal nerve, being more superficial, 

 is thus more liable to injuries; other than this, it is hard to tell 

 why the left side is more frequently affected. The dilators undergo 

 fatty degeneration, and, the air striking the vocal cords, causes 

 vibration of them, and thus produces the sound. Some authors 

 claim the healthy cord is thrown into vibration, thus causing the 

 sound. 



It may depend on tumors in the nose, a thickening of the 

 mucous membrane, fracture of the cartilage of the trachea. In 

 some cases fibrous bands have been found; tumors in the chest 

 also produce this sound; alteration in the shape of the trachea, 

 the result of high checking, or traumatisms. 



Hereditary tendency comes into play; the horses with Roman 

 noses and long, thin necks seem to be more predisposed than the 

 others; also, those of a lymphatic disposition, which are liable to 

 lymphatic disorders, and in this way causing pressure on the nerve. 



How is roaring diagnosed ? 



There are two degrees of the sound produced, which differ in 

 tone and quality. When it is liigh pitched it is called wliistUng, and 

 the animal is known as a whistler; when it is of a loiu pitch it is 

 called roaring, and the animal is called a roarer. Percival experi- 

 mented on these cases, and found that the greater the constriction 

 the more high-pitched the sound. 



The best way to detect these cases is to give the animal a 

 sharp gallop, and especially up grade (as up a hill), and then, having 

 the animal stop suddenly, listen to his breathing; or back the 



