582 sroKADic diseases. 



It is very true that division or ligature of either of the reciir- 

 reuts will be succeeded by roaring, and tumours involving the 

 riecurrents may cause the same symptom ; and Dr. Warburton 

 Begbie says that "no more interesting variety of local paralysis 

 exists than that which is due to the interference with the 

 recurrent or motor laryngeal nerve, produced by an aneurism of 

 the arch of the aorta, or by a cancerous mediastinal tumour. 

 AVell-marked atrophy of the muscles of one side of tlie larynx 

 has, under such circumstances, been found." But in the form 

 of disease involving the laryngeal muscles, which commonly 

 causes roaring, there is no change in the nerve itself, nor can 

 the loss of motor power be traced to pressure upon the nerve 

 trunk by any tumour, aneurism, or adventitious substance. 



The disease of the muscles is, however, essentially nervous in 

 its origin, and may, I think, be classified as a form of wasting 

 palsy — paralysis attophica-^originating in the laryngeal muscles 

 themselves. Wasting palsy is defined by Dr. William Koberts, 

 in Eeynolds' System of Medicine, to be " an atrophic degenera- 

 tion of certain groups of muscles, independent of any antecedent 

 loss of mobility, or of any metallic poisoning." 



I have already stated that the atrophic change is usually seen 

 on the left side of the larynx. It, however, by no means follows 

 that the muscles of the right side are entirely free from disease ; 

 indeed, in many instances, they distinctly partake of the atrophic 

 change, though to a less extent. 



Why the change is greater on the left than on the right side, 

 is one of those things for which no more satisfactory explanation 

 can be given, than why the ulcers of glanders are oftener seen 

 in the left than in the right nostril. 



Eoaring is generally gradually developed. At first, the sound 

 may be intermitting, and days or even weeks may elapse during 

 which the animal may make no noise, although put to severe 

 exertion, as if the muscles had, at the time the sound was 

 emitted, been debilitated from some ephemeral disturbance of 

 nutrition. As the loss of muscular substance progresses, there 

 is a corresponding and permanent loss of power, and what at first 

 was intermitting is now a permanent infirmity. This intermis- 

 sion of the sound is not, however, the ordinary method by which 

 the disease manifests itself. More commonly the noise or roar, 

 slight at first, gradually, but often very slowly, increases in 



