34 DISEASES OF THE LARYNX 



It seems as if heredity played a part in that stalhons and 

 mares which are roarers transmit the tendency to their 

 progeny. The condition usually does not develop until 

 about the fourth to sixth year. As a rule, only the left 

 side is affected, although exceptions are noted. 



Secondarily, recurrent paralysis may be a sequel to 

 influenza, strangles, and dourine, or it may follow an attack 

 of forage poisoning or poisoning with lead or, more rarely, 

 goitre or direct injury to the nerve itself. 



Symptoms. — ^Usually in primary cases the disease comes 

 on gradually. It is at first but slightly developed, the 

 patient only emitting a noisy sound when exercising. As a 

 rule, if the horse be at rest no signs of the disorder are 

 noticed. If the upper rings of the trachea be pinched a 

 prolonged, hoarse throat cough is heard. In many instances, 

 however, cough is absent. It is sometimes possible to 

 cause the patient to emit a peculiar grunt if it is struck a 

 sudden, unexpected blow with the hand on the side of the 

 chest. The principal symptom of roaring, however, is the 

 audible laryngeal sound emitted during and increased by 

 exercise. The quality of the sound suffers many modifica- 

 tions from a whistle to a pronounced roar, which in some 

 animals can be heard a distance of several yards. Pressing 

 the left or right arytenoid cartilage with the index finger 

 increases the sound. In well-developed cases sufiicient 

 exercise can produce apnea. By compressing the nostrils 

 to one-half their normal dilatation the sound is temporarily 

 diminished. Generally the roaring sound ceases after five 

 to ten minutes' rest but returns again during exercise. In 

 mild cases it stops as soon as the animal is "pulled up" 

 after a hard gallop. In bad cases the dyspnea is both ex- 

 piratory and inspiratory. 



Diagnosis. — ^The examination of the patient should be 

 made under motion. The horse may be ridden, galloped on 

 a lunging line or led behind a buggy. In some mild cases 

 the animal may suppress the sound by extending the head. 

 To avoid this the head should be drawn in, the neck held 

 well arched. The use of the laryngoscope which shows the 

 asymmetry of action of the arytenoids is of great value in 

 diagnosis. 



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