FREQUENCY AND CHARACTER OF RESPIRATORY MOVEMENTS 477 



must be sought in the sudden distention of the air vesicles and the flow 

 of the air through the fine bronchioles into the enlarged infundibula. 

 The coincidence that this murmur is especially distinct in children, 

 is referable to the smaller caliber of their infundibular spaces. 

 Furthermore, the quaUty of this sound is generally modified by the 

 noises which are set up by the air as it rushes through the trachea and 

 bronchi. They are transmitted from here to other regions of the pul- 

 monary parenchyma. F6r this reason, the general vesicular murmur 

 is usually regarded as being due to two causes, namely, to the true 

 vesicular sound produced in the infundibula, and the glottic sound, 

 generated by the current of air as it traverses this aperture. Conse- 

 quently, the more remote regions of the lung give rise to a vesicular 

 sound of purer quality than those situated nearer the larynx. In 

 large animals, in fact, this resonant element fails to be transmitted 

 to the more distant pulmonary tissue and can only be heard in the 

 regions adjacent to the bronchioles. It is possible to destroy the 

 glottic element of the murmur entirely by permitting the animal to 

 breathe through an opening in the trachea. 



On listening over the larynx, trachea or bronchi, either with the 

 unaided ear or with a stethoscope, a loud blowing noise is heard dur- 

 ing inspiration as well as during expiration. It is called the bronchial 

 murmur. During health this sound is not audible over the outlying 

 districts of the lung, but is propagated into these regions if the alveoli 

 are deficient in air. A condition of this kind arises quite commonly 

 from compression of the pulmonary parenchyma or in consequence 

 of exudations of inflammatory material (pneumonia) and hence, 

 bronchial breathing over any part of the lung other than that adjoin- 

 ing the larger air-tubes is always indicative of consolidation of this 

 tissue. It might also be mentioned that the absence of these sounds 

 does not necessarily imply that the underlying lung tissue is not being 

 expanded, because the sounds may be prevented from reaching the 

 ear by fluid effused into the pleural cavity (pleurisy). 



The Changes in the Intrathoracic, Intrapulmonic and Intra- 

 abdominal Pressures. — It has previously been shown that the recoil 

 of the stretched tissue of the lungs sets up a pressure in the intrapleural 

 and mediastinal spaces which is negative to that inside the respiratory 

 passage. Knowing its cause, it may justly be assumed that the in- 

 spiratory enlargement of the chest increases this negativity still 

 further, because the lungs are subjected to a somewhat greater elastic 

 tension during this period. The expiratory movement, on the other 

 hand, diminishes the elastic pull of these organs, and hence, also the 

 intrathoracic pressure, i.e., it permits the pressure to approach that of 

 the atmospheric air or zero-line. These changes may be followed 

 more closely by connecting the intrapleural space with a water man- 

 ometer in the manner previously described. With the chest in the 

 static position the intrapleural pressure amounts to about —5 mm. 

 Hg, i.e., to 760 mm. Hg atmospheric pressure minus 5 mm. Hg produced 



