122 Roaring in Horses. 



undue blood-pressure attending such severe and abnormal 

 exertion, and become greatly distended — the greater pro- 

 portional increase in its circumference, and which Stahel 

 describes as " Spindelbildung," being probably in conse- 

 quence of a sudden change or twisting in its direction 

 during distension. This will impose a condition of alter- 

 nate extreme tension and relaxation on the nerve, which 

 must be highly unfavourable for its functions and histo- 

 logical arrangement in the almost embryonic state in which 

 it yet is in such juvenile creatures. In the course of a very 

 few generations we can reasonably infer that, in families 

 which may perhaps have some anatomical peculiarity in the 

 disposition of this nerve in the chest, the weakness induced 

 in this way will become inherited — as other defects often 

 are ; and the predisposition thus existing, Roaring is 

 developed when certain predisposing or exciting causes, be 

 they ever so slight, come into operation. Of course, this 

 line of reasoning can only apply to young race-horses, not 

 to other or adult horses. 



Chronic Roaring not unfrequently follows certain diseases, 

 chiefly those in which the respiratory apparatus in the 

 chest is involved, and particularly those parts of this 

 apparatus which are more or less closely related to the left 

 recurrent lung. Pleurisy, inflammation of the right lung or 

 the pericardium, or of the lymphatic glands in the vicinity 

 of the nerve, are often followed by Roaring, from the exten- 

 sion of the inflammation to it, or the pressure exercised on 

 it by inflammatory products. In this way it is often a 

 sequel of influenza, and similar febrile disorders in which 

 the chest is aff'ected. What are called " colds," which may 

 be bronchitis or pleuro-pneumonia, in addition to catarrh, 

 often have this result. The infectious fever known as 

 "Strangles," in which there is abscess formation in the 

 submaxillary lymphatic glands, is perhaps the most frequent 

 cause of Roaring met with among army horses, and prob- 

 ably also among others than these. The occurrence of this 



