130 THE CANADIAN HOESE 



we believe it is also hereditary — as it is a well-known fact, 

 feotli in Canada and in Britain, that certain breeds of horses 

 are peculiarly liable to this disease. It may also be caused 

 by some lesion or derangement of some of the nerves. 

 " Percivall mentions the following experiment made by the 

 late Mr Field of London. Having ascertained that the organs 

 of respiration of a horse 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 of it excised ; and 

 immediately, on only trotting the horse a short distance, 

 such a degree of roaring was occasioned, that had the exer- 

 tion been continued he would 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 usual 

 condition of wasted muscles on the side deprived of the 

 influence of the recurrent nerve." 



Symptoms.^-'When the horse is not excited, and so long as 

 the air passes in a uniform rate through the larynx and 

 windpipe, the aniiial does not feel any inconvenience ; when- 

 ever he is excited or gaUoped, causing a rush of air, the 

 roaring noise is produced. The sound in ordinary circum- 

 stances is only produced on inspiration, but in very, severe 

 cases the sound is audible both on inspiration and expiration. 



In some horses roaring is difficult of detection. There 

 are several tests which can be resorted to with the 

 view of detecting it. It may often be readily detected by 

 taking the horse firmly by the head and striking him 

 suddenly on the side, causing him to start forward ; if a 

 grtmting noise is emitted it is always a suspicious circum- 



