CHAPTER VIII. 



CAUSES OF CHRONIC ROAKIKG. 



The causes of Chronic Roaring may be considered as 

 " mechanical " and " pathological ;" the first being related 

 to the impediment in respiration which occasions the noise, 

 and the second to the morbid changes to which the impedi- 

 ment is due. We will study the causes in this order. 



Mechanical Causes. 



It has been already stated that the abnormal sound heard 

 in respiration is coincident with the act of inspiration — at 

 least it is loudest then ; for in advanced stages there is a 

 more or less audible noise also during expiration. The way 

 in which the noise or stridor is produced, and the parts 

 which produce it, has afforded matter for discussion for a 

 long time ; but remembering the physiology of respiration, 

 and the share the larynx takes in this function, there should 

 not be much doubt as to the origin of the noise. 



We have seen that, during breathing, the aryttenoid carti- 

 lages, and the vocal cords attached to them, are moved out- 

 wards and upwards in inspiration, so as to widen the glottis 

 and allow the necessary volume of air to pass through to 

 the lungs, the degree of movement depending upon the 

 physiological requirements of the body. In tranquil respira- 

 tion the movement is only trifling, as the space existing 

 between the vocal cords {pars vocalis) and their movable 

 cartilages (pars respiratoria), when they are at rest in the 

 living animal, is almost sufficient for the admission of the 



