12 .Roaring in Horses. 



And in 1840 he shows that opinions were much divided as 

 to the principal cause. 



But, previous to this period, Youatt, in his lectures on 

 horses, when treating of Eoaring and its causes, remarks : 

 " In the far greater number of cases there is distortion, 

 rendering the muscles on one side useless, and therefore 

 causing them to waste away. . . . The wasting of the 

 muscles is, therefore, the efect, and not the cause, of that 

 which produces Roaring. "^ 



About this time Field observed that a frequent cause of 

 Eoaring, in cases of ulceration of the rima glottidis, was 

 spasm of the glottis. " While the horse is suffering great 

 pain from the passage of the air over these denuded 

 surfaces, the instinctive action of the muscles, more power- 

 ful than the will of the animal itself, partially closes the 

 air-tube, and thus lessens the irritation. I have seen many 

 cases of this kind, and by opening the trachea have 

 obtained immediate relief" 



This hypothesis, however, presumably did not satisfy 

 Mr. Field, for we find him repeating one of Dupuy's 

 experiments, by producing Roaring in a horse, and demon- 

 strating the cause of laryngeal muscular atroph}^ " Having 

 ascertained that the organs of respiration of a horse used 

 for farm work were sound, I cast him, and laid bare the 

 recurrent nerve of the off-side, and passed a ligature 

 loosely around it. He was then allowed to get up, and, 

 after a few minutes, galloped severely without evincing the 

 slightest defect in his breathing. The nerve was then 

 drawn out by the ligature, and one inch and a half excised; 

 and immediately on trotting the horse a short distance, 

 such a degree of roaring was occasioned that, had the 

 exertion been continued, he would soon have fallen. I kept 

 this horse four years, and though his breathing became 

 much better, he continued a sad roarer. At the end of that 

 time I destroyed him for the larynx, which exhibited the 



1 " The Veterinarian,", vol. vi., p. 183. 



