ELEMENTS OF HIPPOLOGY. 163 



muscles of the cell walls lose their elasticity or become partially 

 paralyzed. 



Broken wind is easily distinguished from other lung 

 disease by the double effort to exhale air, usually accom- 

 panied by a hacking cough. The period of exhalation is longer 

 than the period of inhalation. Heaves, except in very mild, 

 recent cases, is incurable, and the horse is greatly disabled by it. 



Roaring is a disease that is characterized by a peculiar 

 noise made by the horse at inhalation. The noise called roaring 

 may be made by a sound horse when excited, or when suddenly 

 put to exertion after a period of idleness, or on account of a 

 cramped position of the head or neck. This noise is not accom- 

 panied, in the sound horse, by evidences of fatigue and ina- 

 bility to perform work, as is the case in the unsound horse. 

 Chronic roaring is the result of a paralysis of the muscles of the 

 larynx that control the vocal cords. This paralysis prevents 

 them from being opened sufficiently wide to admit air without 

 vibrating. Often a horse maybe affected by the disease — par- 

 alysis of the vocal cord — without the accompanying sound. 

 This can be detected by making a sudden motion towards the 

 flank with the hand or whip, when the unsound animal will 

 grunt or groan. Roaring is very disabling, and can be cured 

 only by a surgical operation. This operation consists in re- 

 removing the vocal cord that has become uncontrollable. 



Whistling is a variation of the sound made by a roarer. A 

 horse with a severe sore throat may make a whistling sound at 

 inhalation. This should not be considered as evidence that he 

 is a roarer until the sore throat is cured, when, if the horse is 

 sound, the whistling will cease. - 



A sound horse should breathe noiselessly and easily in all 

 emergencies. A horse that makes any noise or has any diffi- 

 culty in its breathing, no matter how slight, should not be 

 considered sound. 



