198 CLINICAL BACTERIOLOGY AND 



mucosae acting as an excellent medium upon which a 

 rich bacterial growth is taking place. Consequent upon 

 this growth the whole surface is bathed with endotoxins 

 and exotoxins derived from the pathogenic bacteria. 



Absorption of these takes place into the deeper 

 structures, including the muscular elements of the larynx 

 extending to the nerve endings, the nerve fibres, and nerve 

 trunks themselves, and, according to the structures 

 involved, we now find a specific mucositis, cellulitis, 

 myositis, and neuritis set up. This is followed by 

 degenerative changes ; the trophic functions of the re- 

 current nerve are soon interfered with, and muscular 

 atrophy is the result. These conditions are aggravated by 

 the strain placed upon the already depressed set of 

 muscles, and the degenerative changes which have already 

 taken place in the nerve are increased by the jerking of 

 the aorta round which the nerve passes. 



The muscles on the right side of the larynx are subject 

 to the same degenerative causes, and no doubt temporary 

 atrophic changes take place, but owing to the different 

 disposition of the nerve-supply, the trophic interference is 

 not called into play. 



Undoubtedly there are cases where the mildness of the 

 attack has only been capable of producing slight degenera- 

 tive and organic changes both in the muscles and the 

 nerve, and, given time, a complete recovery follows. This 

 may explain a very common fact we see in practice — 

 namely, an animal recently recovered from a catarrh, etc., 

 may be a pronounced whistler, and even a roarer, and, in 

 time, with exercise, good food, and conditioning, may be- 

 come quite sound in his wind, the obvious conclusion being 

 the retrogressive changes were so slight that Nature was 

 able to bring about a complete restoration before hopeless 

 organic chaos took place. 



If these foregoing conclusions are correct, it is obvious, 

 if we succeeded in preventing bacterial invasions to the 

 upper air passages, we should hear very little of roaring 

 and whistling in horses, but such a task, of course, would 

 scarcely be practicable. We can, however, reduce the 

 severity of a bacterial attack, and in many cases even 

 prevent its development altogether by sero- vaccine therapy. 



It may be pointed out heredity plays an important part 

 in the production of roarers and whistlers, and with this, 

 in a limited sense, we agree. Conformation is undoubtedly 



