4iZ DISEASES OF THE AIR-PASSAGES. 



deformity, or want of elasticity in it ; or by actual obstruc- 

 tion within it : and this difference of causation, together 

 with the part or place in which it exists, will serve stiil 

 further to account for the various kinds of — or rather sounds 

 emitted in — roaring. 



The kind or nature of the sound, therefore, will be 

 found to be referable — first, to the nature of the impedi- 

 ment or obstruction; secondly, to the degree or extent to 

 which it exists ; thirdly, to the situation of it. To illustrate 

 this by example, we may expect a different sound from 

 thickening of the membrane, ov general diminished caliber of 

 the passage, from what either ulceration, or ossification, or 

 partial diminution or impediment, would produce; this 

 sound will vary again, according to the degree of thickening, 

 or contraction, or ulceration, or ossification; and, thirdly, it 

 will undergo modification, according to the part whose 

 lining membrane is thickened, or ulcerated, or ossified : 

 according, in fact, as its seat happens to be the nasal cham- 

 bers, the larynx, the windpipe, or the bronchial tubes. I 

 do not mean to assert that all this can be realised in prac- 

 tice. Unfortunately for us, I am afraid we shall find our 

 art not sufficiently advanced to connect the sound, in most 

 cases, with the seat and nature of the cause ; but I mean 

 to contend, that, if we would set about the investigation as 

 men of science, all these considerations must of necessity 

 enter into our theorification. 



Under what circumstances is the sound emitted ? — 

 When any sudden effort or exertion is made, or any hard or 

 fast work performed — whenever, in fact, the breathing is so 

 disturbed that the current of air through the windpipe is 

 rendered rapid and voluminous. So long as the air passes 

 in a slow and uniform stream through the pipe, as in ordinary 

 breathing, no noise is heard, nor is any inconvenience felt by 

 the animal ; but the moment any rush of air is made, the 

 contraction or impediment, whatever it be, opposing this 

 augmentation of speed and volume, roaring is produced by 

 the vibration of the air against the obstructing body. So 

 long as a horse continues at rest, or goes but at a foot's 



