BODY MOVEMENTS. 227 



ticed only in forcible or increased respiration, and is then 

 characterized by a harsh, sharp inspiratory 

 noise or tone (wheezing, whistling, blowing, hum- 

 ming, roaring, snoring.) The respiratory noise is caused by 

 the fact that deep and rapid inspiration causes the air current 

 to force the paralyzed arytenoid cartilage and vocal cord into 

 the lumen of the larynx and thus obstructs its free passage. 

 Decreasing the volume of the ingoing current of air by com- 

 pressing the nostrils causes the noise to cease. Pressure on 

 the paralyzed arytenoid cartilage increases the noise. Pres- 

 sure on the right (unaffected) cartilage increases dyspnoea to 

 such an extent that inspiration is almost impossible, it ceases 

 entirely or continues with a sharp wheezing sound, because 

 the lumen of the larynx is now obstructed by both arytenoid 

 cartilages. 



In examining- for roaring the horse must be placed 

 under conditions that force it to make rapid and energetic respira- 

 tory movements, it must be "worked hard," pull heavy loads over 

 soft ground, or gallop. Exercising or riding are especially adapted 

 for this purpose because we can control the position of the head, 

 and thus influence respiration. Whether or not the animal is 

 accustomed to this sort of exercise has no effect on the general 

 result. 



If the head and neck of the animal are well checked up and 

 back, the points of insertion of the dorsal muscles are approxi- 

 mated and the action of the latter on the spinal column is reduced: 

 now, in order to fix the spinal column the longissimus dorsi, the 

 inspiratory and the abdominal muscles must be contracted with 

 unusual force; this can be done only at the moment of inspiration. 

 In expiration these muscles are relaxed and the animal loses, more 

 or less, the control over its spinal column. It therefore makes 

 an effort to reduce the expiratory period by rapidly and energetic- 

 ally following with the inspiratory movement. If only one aryte- 

 noid cartilage projects over the lumen of the larynx the inspiratory 

 current forces it in, produces a stenosis and causes the respiratory 

 sound. By turning the head toward the right the in-streaming 

 current of air is directed on the left arytenoid cartilage, and if the 

 paralysis is only an incomplete one the characteristic sound is pro- 

 duced just the same. 



This kind of treatment can never pro- 

 duce roaring in a healthy horse. 



In order to make a positive diagnosis of " r o a r i n g " it 

 is necessary to eliminate the possible presence of acute morbid 



