216 A MANUAL OF PHYSIOLOGY 



ments may occur. In young persons it may be directly observed 

 with the bronchoscope, an instrument used by laryngologists 

 for exploring the larger bronchi, that these dilate in inspiration 

 and constrict in expiration (Ingalls). In part at least these 

 movements are passively produced by the changes of intra- 

 thoracic pressure, but it has not been definitely determined 

 whether they are not in part caused by alternate contraction 

 and relaxation of the circular bronchial muscles. To these muscles 

 has sometimes been attributed the function of regulating the flow 

 of air into and out of the infundibula, as the muscle of the 

 arterioles regulates the distribution of the blood in the organs. 



As regards the respiratory sounds, all that is necessary to 

 be said here is that when we listen over the greater portion of 

 the lungs with the ear, or, much better, with a stethoscope, 

 a soft breezy murmur, that has been compared to the rustling 

 of the wind through distant trees, is heard. This has been 

 called the vesicular murmur. It is only heard in health during 

 inspiration and the very beginning of expiration, and is louder 

 in children than in adults. Around the larger bronchi and the 

 trachea a blowing sound is heard, which certainly originates at 

 the glottis, and is strengthened by the resonance of the air-tubes. 

 In health this is not recognised over the greater portion of the 

 lung. But in certain diseases in which the alveoli are filled up 

 with exudation, this bronchial or tubular breathing may be heard 

 over a large area, the vesicular sound being now suppressed and 

 the bronchial sound being better conducted through the smaller 

 bronchi towards the surface of the lungs when their walls have 

 been rendered more rigid by the solidification of the parenchyma, 

 in spite of the fact that the consolidated tissue as such does not 

 conduct the sound so well as the air-containing alveoli. 



It has been much debated whether the vesicular murmur also 

 arises at the glottis, and is modified by transmission through the 

 pulmonary tissue, or whether it arises somewhere in the terminal 

 bronchi, the infundibula or the alveoli. Both views may be sup- 

 ported by certain arguments, and to both some objections may 

 be raised. The fact appears to be that there are two elements 

 in the inspiratory murmur a true vesicular sound, produced 

 about the place where the terminal bronchioles give off the 

 infundibula, and a resonance sound set up in the trachea and 

 bronchi by the glottic murmur. This resonance sound as heard 

 over portions of the lung containing only small bronchi has a 

 different character from that heard over large bronchi, inasmuch 

 as the fundamental note, and to a still greater extent the over- 

 tones (p. 280), are much weakened in those small and easily- 

 distensible tubes. The true vesicular element is heard all over 

 the lungs, but the resonant laryngeal element in large animals, 



