CAUSES OF UNSOUNDNESS. 135 



in roaring. This is the commonest cause, and one 

 that comes on gradually. Morbid growths in the 

 nasal passage, and in parts in juxtaposition to the 

 upper portion of the respiratory tracts, are occa- 

 sional causes, and these may produce roaring in 

 a gradual manner, or they may give rise to it in- 

 stantaneously. It is important to bear this in mind, 

 should litigation be likely to arise. The sudden 

 development of '' roaring " may occur through 

 the displacement of a stalked morbid growth (poly- 

 poid tumour) over the glottal opening, thus inter- 

 fering with the normal supply of air into the 

 larynx. Intermittent forms of '' roaring " are, some- 

 times, induced in this manner, so that it is quite 

 compatible with pathological facts (of which 

 numerous instances have been recorded) that 

 a horse may be sound in his wind at the time of 

 examination, yet become a " roarer " immediately 

 afterwards. That this is an exceptional cause it 

 must be admitted. In lead-poisoning, and also 

 through feeding upon certain species of vetches, 

 " roaring " has been produced, but a little careful 

 discrimination usually leads one to the cause in this 

 case. From time immemorial it has been customary 

 to regard ''roaring" as a hereditary disease, but 

 whether this is correct has not — so far as the 



