WHISTLING AND ROARING. 451 



ration, is possible ; but that even such destructive treatment 

 will account in full for the origin of these unnatural sounds Ave 

 scarcely believe. Neither is the explanation which is usually 

 given of the greater liability of the laryngeal muscles of the 

 left side to become diseased likely to carry Avith it universal 

 conviction. This latter fact is attempted to be explained from 

 the peculiarity of the thoracic origin of the left recurrent nerve, 

 from which these muscles receive their motor-poAver. 



Its origin being more posterior than that of the right, it has 

 been suggested that in this way it is more readily and more 

 largely influenced by morbid actions Avhich occur in the cavity 

 of the thorax. Noav, although roaring is often a sequel of 

 diseases of the respiratory organs, it is certainly more liable to 

 folloAV an attack of inflammatory action in the upper than the 

 loAver air-passages, in the larjaix than in the lungs. This result 

 Ave should not expect to find if it were perfectly true that the 

 existence of pulmonary inflammation Avas largely to deA^elop 

 laryngeal disease through any influence determined to the 

 recurrent nerve. From its being somcAvhat more superficially 

 situated than the right nerve, pressure exercised from Avithout 

 has also been regarded as actively operating in the induction 

 of this defective nutrition Avith its consequent results. If, 

 hoAvcA'er, pressure does operate in the production of this dis- 

 turbance of nerve force and sequences, it seems more likely 

 to do so by acting from Avithin, through textural changes, than 

 by violence from Avithout. 



In estimating the agencies at Avork in the production of 

 this structural change and functional disturbance, there is one 

 Avhich facts and observation teach us is Avidely distributed and 

 constantly prevailing, viz., hereditary predisposition. The fact 

 that both sta,llions and mares, themselves roarers, have begotten 

 and bred animals Avhich ultimately became roarers, is acknoAV- 

 ledged by the more intelligent breeders of horses of all classes. 

 In my oAvn experience I have met with particular sires, roarers, 

 Avhose produce from different mares have in large proportion, at 

 an early period of life, and apart from any apparent cause, as 

 disease of the respiratory organs, shoAvn unmistakable evidence 

 of defective respiration ; also, I am aAvare of mares, themselves 

 roarers, Avhose produce by difl'erent sires, not sufferers from 

 this disease, Avere similarly affected to their dams, 



29—2 



