Causes of Chronic Roaring. 115 



The noise heard in expiration in these cases is caused 

 by the air pushing past, and lifting to one side, the ob- 

 structing cord and cartilage. 



It has been denied that the immobile Tocal cord has 

 anything to do with the production of the noise in Roaring; 

 but that it must have a large share in this, might be inferred 

 from the anatomical and physiological facts which I have 

 given, as well as those of a pathological kind, derived from 

 observation of morbid conditions of the vocal cords in man 

 and animals. 



The distension of the ventricle with air would alone pro- 

 duce noisy respiration. Falconioi describes a case of sub- 

 mucous emphysema of this ventricle in a horse, through air 

 obtaining access to the cellular tissue ; this condition caused 

 a whistling sound in breathing. Such an accident may be 

 more frequent than might be supposed, judging from the 

 extreme rarity of the recorded instances ; as stalks of 

 fodder may readily wound the mucous membrane at this 

 part. Giinther reports the case of a horse in which the 

 ventricle was filled with pus, and which caused a noise in 

 breathing ; the sound disappeared when the pus escaped. 

 Moller had a similar case. 



The difference in the dimensions of the air-passage 

 during deep inspiration in the healthy larynx, and in that 

 of a horse affected with Roaring, will be better realised, per- 

 haps, by comparing fig. 6 (p. 91) with fig. 7 (p. 113). 



Pathological. Causes. 



Having considered the mechanical causes of Roaring, we 

 will now inquire into the pathological conditions which lead 

 to these impediments. 



Beginning with the fully ascertained fact, that debility or 

 atrophy of the left dilator muscle is the causa proxima of 

 chronic Roaring, the questions to be . answered are : why 



' " Griornale di Anatomia, Fisiologia," etc., 1886. 



8—2 



