MECHANICAL PHENOMENA OF EXTERNAL RESPIRATION 23 z 



may be heard over the affected area. The bronchi themselves, how- 

 ever, must still be patent and contain air. The most commonly 

 accepted explanation is that the laryngeal sound is 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 

 seems probable that, in addition, the columns of air in the bronchi* 

 which are encased in solid tissue, may actually increase the intensity 

 of the transmitted laryngeal murmur by resonance. 



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 supported 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 overtones 

 (p. 304), 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, like the horse and ox, 

 dies out as an audible murmur before it reaches the remotest lobules, 

 and can only be distinguished over a portion of the pulmonary area. 

 When the glottic sound is eliminated by causing an animal to breathe 

 through a tracheal fistula, the vesicular murmur is still heard, and in 

 the horse is even somewhat sharper than normal, although in the dog 

 it is softer and weaker. The expiratory murmur does not seem to 

 contain a true vesicular element, but is exclusively due to the resonance 

 of the expiratory glottic sound (Marek). It is generally admitted, and 

 this is of great importance in practical medicine, that when the normal 

 vesicular sound is heard over any portion of the lung tissue, it may be 

 inferred that this portion is being properly distended, and that air is 

 freely entering its alveoli. 



Up to this point we have contented ourselves with a purely 

 qualitative description of the mechanical phenomena of respiration. 

 We have now to consider their quantitative relations, and the 

 methods by which these have been studied. 



The expansion of the lungs in inspiration may be easily demonstrated 

 in man, and even a rough estimate of its amount obtained, by the clinical 

 method of percussion. For example, the resonant note that is elicited 

 when a finger laid on the chest at a part where it overlies the Bright 

 lung is smartly struck can be followed down until it is lost in the ' liver 

 dulness.' If the lower limit of the resonant area be marked on the 

 chest-wall first in full inspiration, and then in full expiration, the mark 

 will be lower in the former than in the latter, and the difference will 

 represent the difference in the vertical length of the shrunken and dis- 

 tended lung. A similar enlargement in the transverse direction may 

 be demonstrated in the same way, the inner borders of the lungs coming 

 nearer to the middle line in inspiration, and receding from it in expira- 

 tion. The examination of the chest by the Rontgen rays has also 



