THE MECHANICS OF RESPIRATION 343 



by the fact that, in the region immediately surrounding a localized con- 

 solidation, a fluid has increased resonance, which would not be the case 

 if the relaxation produced was equally distributed throughout the lung. 

 The root of the lung, which has generally been regarded as more or 

 less fixed, undergoes in normal breathing a definite forward, downward 

 and outward movement, and the heart shares in this movement (Keith). 

 The movements of .the lower ribs and diaphragm are responsible for the 

 expansion of the lower lobes and dorsal portion of the upper lobes of the 

 lungs, whereas the movement of the upper five ribs expands the anterior 

 portion of the upper lobes. The relative infrequency of pleuritic fric- 

 tion-sounds and pain over the upper lobes as compared with their fre- 

 quency over the lower lobes is explained by the fact that the expansion 

 of the upper lobes is accomplished with little displacement of the pleural 

 surfaces, whereas in the lower lobes expansion is accompanied by a glid- 

 ing of the lungs across the ribs. 



