118 Roaring in Horses. 



up the neck will give rise to precisely the same symptoms 

 and the same morbid alterations on the right side of 

 the larynx as when this is performed on the left nerve. 

 External injury, or alterations in the nerve-structure, 

 due to changes in its histological elements, will modify 

 or altogether abolish the conductibility of a nerve. Such 

 are in operation in the development of chronic Koar- 

 ing. Pressure upon, or disease of the nerve, in any part of 

 ics course, from its origin close to the heart up lo its arrival 

 at the larynx, will impair or destroy its function, and in 

 time alter its structure. 



How is this pressure or disease brought about ? Any 

 change affecting other organs or tissues in immediate 

 proximity to the nerve will affect it. Aneurism of the aorta, 

 tumours, inflammation or disease of any portion of the 

 pleura with which the nerve is in contact ; inflammation, 

 hypertrophy, and induration of the lymphatic glands in any 

 part of its course, or any other morbid conditions in which 

 it may be involved either directly or indirectly, will impair 

 its use either partially or wholly, temporarily or per- 

 manently. 



Perhaps, of all causes, the pressure or disturbance exercised 

 by diseased intra-thoracic lymphatic glands — chiefly the 

 bronchial — is the most frequently observed. So long ago 

 as 1838, Ferguson, when examining the body of a horse 

 which had been a Roarer for a long time, found the left 

 recurrent nerve enveloped and compressed by a voluminous 

 indurated bronchial lymphatic gland, while the remainder 

 of the nerve between this gland and the larynx was quite 

 different to that on the opposite side, it being greatly 

 wasted and its flbres scarcely distinguishable. All the 

 laryngeal muscles which received filaments from it were so 

 completely atrophied, that it was diflicult to perceive their 

 structures, while the glottal opening was twisted and the 

 borders of the aryta^noid cartilage partly obstructed it.^ 

 1 " The Veterinarian," 1838. 



