Causes of Chronic Roaring. 127 



Roarer, and remained so during the winter, but in July of 

 the same year it was passed sound by a veterinary surgeon, 

 the noise having disappeared." 



So far, then, there does not appear to be anything 

 mysterious in the constancy with which the immediate 

 cause of Roaring is found to be localised on the left side of 

 the larynx ; it is simply due to the fact that the left recur- 

 rent nerve in the chest is exposed to injurious influences 

 from which the right nerve is altogether exempt ; and that 

 these influences are many and diverse, we know full well. 

 When one or more of these influences act upon the nerve, 

 weakening of the muscles it supplies is soon manifested ; 

 and the first muscle to be affected being the left dilator, a 

 noise in respiration becomes evident, through imperfect 

 opening of the glottis. The rapidity with which the 

 inspiration becomes impeded, and the noise grows louder, 

 will depend upon the extent to which the conductibility of 

 the nerve is involved. Outside the chest, both nerves are 

 alike exposed to injury ; but as it is indeed rare to find the 

 right side muscles of the larynx wasted, the risk of damage 

 in the region of the neck must be infinitely small. 



