DISEASES OF THE EESPIKATORY ORGANS. 583 



intensity, thus marking or indicating tlie progress of the muscular 

 change, and inability to dilate the laryngeal opening. 



Causes. — Putting aside all exciting causes of alteration of the air 

 passages, to be hereafter mentioned as causes of roaring, I think 

 that laryngeal muscular atrophy is due to hereditary predisposi- 

 tion ; and it is a well-known fact that certain breeds, the produce 

 of certain sires, are nearly all roarers. I have repeatedly observed 

 this, not only in racers, but in other breeds of horses. Indeed, I 

 know one breed of Clydesdales which are nearly all roarers, both 

 mares and horses. Horses and geldings are, however, more 

 liable to become roarers than mares, which seldom, except where 

 the hereditary taint is very strong, become roarers. Small 

 ponies are scarcely ever affected, although they are subject to 

 colds, laryngitis, and pulmonary diseases. 



A horse predisposed to become a roarer generally suffers 

 from laryngeal irritation from trivial causes, and usually the 

 infirmity appears after repeated attacks of cold and sore throat. 



Other causes of Roaring. — Concluding that the majority only 

 of cases of roaring are due to the condition described, it is 

 necessary to mention that the sound may arise from other and 

 incidental conditions which, although not so frequent, are quite 

 as important. 



Koaring may be due to disease of the nose, nasal polypi, 

 depression of the nasal bones from previous fracture (see Prin- 

 ciipUs and Practice of Veterinary Surgery), osseous tumours in 

 the nostrils ; closing of one nasal chamber by false membrane 

 or disease of the bones ; tumours on the posterior nares, called 

 " bellones " by horse-coupers, falling into the glottidean opening, 

 causing intermitting roaring; constriction of the trachea ; tumours 

 in the thoracic cavity ; distension of the guttural pouches ; 

 disease of the pharyngeal and parotidean Ij^mphatic and salivary 

 glands ; tight reining ; fractures of the tracheal rings, or any 

 cause of distortion of the larynx. 



In addition to the sound emitted during inspiration, the roarer 

 generally has a cough which is diagnostic, being a loud, harsh, 

 dry sound, half roar, half cough ; and the generality of roarers 

 are also grunters. It will also be found that the sensibility of the 

 larynx is diminished in confirmed roarers, and that consequently 

 it is difficult to make them cough in the ordinary way by press- 

 ing the larynx. In testing a horse for its wind, it is usually the 



