102 



The paralysis of the muscles is due to derangement of the nerve that 

 supplies them with energy. The muscles of both sides are not supplied 

 by the same nerve; there is a right and a left nerve, each supplying its 

 respective side. The reason why the muscles on the left side are the 

 ones usually paralyzed is owing to the difference in the anatomical 

 arrangement of the nerves. The left nerve is much longer and more 

 exposed to interference than the right nerve. This pair of nerves is 

 given off from its parent trunks (the pneumogastrics) after the latter 

 enter the chest, and consequently they are called the recurrent laryngeal 

 nerves, on account of having to recur to the laryux. 



In chronic roaring there is no evidence of any disease of the larynx, 

 other than the wasted condition of the muscles in question. The dis- 

 ease of the nerve is generally located far from the larynx. Disease of 

 parts contiguous to the nerve along any part of its course may interfere 

 with its proper function. It is not really necessary for the nerve itself 

 to be the seat of disease ; pressure upon it is sufScient; the pressure of 

 a tumor on the nerve is a common cause. Disease of lymphatic glands 

 within the chest through which the nerve passes on its way back to the 

 larynx is the most frequent interruption of nervous supply, and conse- 

 quently roaring. When roaring becomes confirmed medical treatment 

 is entirely useless, as it is imjiossible to restore the wasted muscle and 

 at the same time remove the cause of the interruption of the nervous 

 supply. Before the disease becomes permanent it may be benefited by 

 a course of iodide of potassium, when it is caused by disease of the 

 lymphatic glands. Electricity has been used with indifferent success. 

 Blistering or firing over the larynx is of course not worthy of trial if 

 the disease is due to interference with the nerve supply. The adminis- 

 tration of strychnia (nux vomica) on the ground that it is a nerve tonic, 

 with the view of stimulating the affected muscles, is treating only the 

 result of the disease without considering the cause, "and is therefore use- 

 less. The operation of extirpating the collapsed cartilage and vocal cord 

 is believed to be the only relief, and as this operation is critical and can 

 only be performed by the skillful veterinarian, it will not be described 

 here. 



From the foregoing description of the disease it Avill be seen that the 

 name "roaring," by which the disease is generally known, is only a 

 symptom and not the disease. Chronic roaring is also in many cases 

 accompanied by a cough. The best way to test whether a horse is a 

 "roarer" is to either make him pull a load rapidly up a hill or over a 

 sandy road or soft ground; or if he is a saddle horse gallop him up a 

 hill. The object is to make him exert himself. Some horses require a 

 great deal more exertion than others before the characteristic sound is 

 emitted. The greater the distance he is forced the more he will appear 

 exhausted if he is a roarer; in bad cases the animal becomes utterly 

 exhausted, the breathing is rapid and difficult, the nostrils dilate to the 

 fullest extent, and the animal appears as if suffocation was iuimineut. 



