Paralysis of the Recurrent Nerve. 729 



6. Paralysis of the Recurrent Nerve. 



{Roaring, Laryngeal Hemiplegia.) 



Historical. The connection between roaring and paralysis of the 

 recurrent nerve was first demonstrated by Dupuy (1830) and Youatt 

 (1833) showed that the paralysis of the nerve is followed by atrophy 

 of the muscles supplied by it. The true nature of the disease was 

 first explained fully by Giinther (1834). Within recent years 

 (1902) the experiments of Thomassen and the histological investiga- 

 tions of Llihrs (1904) have added considerably to our exact knowledge 

 of the condition; and the clinical observations of Dieckerhoff (1900), 

 and the work of Schindelka and Polansky (1889), and of Malkmus 

 (1897) have also added greatly to our knowledge of the subject. 



Occurrence. Roaring is exceedingly common in horses in 

 England, France, Hanover, Holstein, Austria and Hungary and 

 in countries in which horses, and especially thoroughbreds, are 

 bred in conjunction with intensive agriculture. In the Argen- 

 tine Republic and in South America generally, in Egypt, India, 

 Arabia and Australia the disease is rarely met wdth (Nocard, 

 Fleming). Isolated cases occur in the other species. 



Etiology. Recent investigations appear to support the 

 view that in the immense majority of cases infectious diseases 

 are to blame for the causation of recurrent paralysis. Experi- 

 ence shows that the disease is a common sequel to strangles, 

 pneumonia or infectious sore throat, and it is worthy of notice 

 that in all these three diseases the streptococcus equi is more 

 or less concerned. The effect of strangles is shown clearly in 

 that in the Argentine Republic, wdiere strangles and pneumonia 

 are not of common occurrence, paralysis of the recurrent nerve 

 is only exceptionally observed (Nocard), while the part played 

 by pneumonia is showm by the records of the Prussian army in 

 wdiich 0.4 to 2.8 per cent of the animals affected w4th pneumonia 

 afterw^ards become roarers. In these cases the paralysis is 

 principally due to inflammation caused by bacterial toxins cir- 

 culating in the blood. In a case recorded by Frohner there w^as 

 paralysis of the nerve due to dourine. 



It was shown ])y the histological investigatious of Thomassen that there was 

 a degeneration of the nerve fibers which reached a maximum in the immediate neigh- 

 borhood of the larynx and that the alterations gradually became less pronounced 

 in the central direction until they had entirely disappeared in the nerve in the 

 lower portion of the neck or in the chest cavity. There were no changes in the 

 fibers running in company with the vagus itself. Apparently the toxin tends to 

 affect the distal portion of the nerve. In many cases of pneumonia the paralysis 

 may be produced by extension of inflammation in the left thoracic cavity to the 

 nerve lying in the subpleural connective tissue. 



In a proportion of cases a causal connection can be traced 

 betw^een the disease and certain poisons. Thomassen proved 

 experimentally beyond a doubt that in the horse lead is capable 



