730 Paralysis of the Recurrent Nerve. 



of causing degeneration of all the branches of the vagus, the 

 degeneration being most pronounced in the terminal portion 

 of the left recurrent nerve. The observations of Beckmann 

 and Schmidt yielded the same results; animals working in 

 the neighborhood of lead works are affected in large num- 

 bers. In rare cases the disease may be caused by long-con- 

 tinued feeding on certain foods, riga pea, chick pea, lucerne. 

 Whether the disease in these cases is due to a lesion of the 

 nucleus, as supposed by Leather and Cadeac, or to a peripheral 

 disease, is not definitely known. In view of the fact that the 

 foods mentioned are not generally responsible for any such 

 effect it must be supposed that they are capable of affecting the 

 nerve injuriously under certain circumstances only. Verrier 

 was able to demonstrate the toxic effect of the Lathyrus cicera 

 experimentally, while Agonigis' experiments were negative. 

 The cause of the suddenly occurring paralysis observed by 

 Friis and Miiller in a number of horses after feeding on mo- 

 lasses is quite unknown. 



Other causes play a small jjart in the production of the 

 disease. Diseases of this kind are observed more frequently in 

 the other species. Aneurism of the aortic arch may cause 

 pressure on the nerve, as may also tumors at the entrance to 

 the chest, in the neighborhood of the aortic arch, or the trachea, 

 and one branch is as likel}^ to be subjected to pressure as the 

 other. Enlarged lymphatic glands must be considered in this 

 connection and also malignant growths, suppurative inflamma- 

 tion, leucemia and pseudo-leucemia. It is only rarely that the 

 cause of the pressure is enlargement of the thyroid, dilatation 

 of the esophagus or abscess in the neck. 



The recurrent nerve rarely suffers traumatic injury, and 

 when this does happen it is generall}^ the more superficially 

 placed nerve on the left side ; for example in opening an abscess 

 (Kiihnert) or venesection (Giinther). Hutli explains the com- 

 mon occurrence of the disease among geldings on the supposi- 

 tion that the nerve on the left side is injured mechanically while 

 the animal is thrown for the operation of castration. This view, 

 however, is not in agreement with the manner in which the 

 disease develops and its course. 



In many cases rheumatism is supposed to be the cause, but 

 even in these cases the coincident effects of infective materials 

 are not excluded. 



Finally, bulbar paralysis is generally followed by paralysis 

 of the recurrent nerve. Supra-nuclear paralysis lias*not as yet 

 been observed in animals. 



Experience shows that in about 95 per cent of cases the 

 paralysis is on the left side. Attempts are made by many 

 authors to explain this by the peculiar anatomical disposition 

 of the left recurrent nerve. 



The nerve on the left side is considerably lontjer than that on the right. It 

 right into the thorax and turns round the arch of the aorta, while the right 



