DISEASES OF THE RESPIRATORY ORGANS. 581 



ing of the mucous membrane, distortion of the neck by tight 

 reining, the presence of an immoveable tumour in the tracliea, 

 or by any cause which diminishes the area of the passage of 

 the air to and from the lungs. AVhistling, although loudest 

 during the inspiratory movement, is by no means always absent 

 during the expiratory act ; careful auscultation is, however, 

 necessary to detect it. If entirely absent during expira- 

 tion, the seat of the lesion causing it is to be looked for 

 in the larynx or upper part of the windpipe. Whistling, like 

 roaring is often traceable to hereditary taint, and is an un- 

 soundness. 



3. Roaring. — This symptom of disease consists in a loud un- 

 natural sound emitted during the inspiratory act. Roaring is 

 sometimes symptomatic of acute laryngitis, and then only indi- 

 cates a condition of temporary unsoundness. 



The cause of roaring is, however, generally found to be due 

 in the majority of cases to atrophy and fatty degeneration of the 

 muscles of the larynx. The origin of the paralysis is involved 

 in some mystery; but it is generally accepted by veterinarians 

 that, inasmuch as it is generally confined to the left laryngeal 

 muscles, the explanation is to be found in the fact that the 

 recurrent or ascending laryngeal nerve on the left side leaves 

 the pneumogastric further back than on the right, and winds 

 round the posterior aorta; whereas the right is given otf 

 opposite the first rib, winding round the dorsal artery, and 

 consequently the left nerve is more apt to be implicated in any 

 disease of the chest than the right. This explanation is unsatis- 

 factory on many accounts. Is^. Eoaring is not a common sequel 

 to pulmonary disease : 2cl. It is not an accompaniment of thoracic 

 disease, which would most certainly be the case if the nerve 

 were implicated in an inflammatory affection : 2>d. Many roarers 

 whose history has been known from their birth have never 

 suffered from any chest affection, nor indeed from any disease 

 beyond a common cold, and sometimes not even from that slight 

 ailment: 4:th. Mares and ponies are less often affected with 

 roaring than large geldings and stallions, but are quite as sus- 

 ceptible to chest diseases ; and lastly, dissections have failed to 

 discover any change in the nerve trunk itself, although the 

 animals dissected have been confirmed roarers for yen rs previous 

 to their death. 



