THE MECHANICS OF THE RESPIRATORY MOVEMENTS 



459 



Practically the same result has been obtained by connecting a mano- 

 meter with the intrapleural space by means of a hollow tube which is in- 

 serted through an intercostal space (Fig. 235) . On piercing the parietal 

 pleura, the visceral layer is pushed ahead of the probe (P) so that its free 

 end comes to lie in a recess of the intrapleural cavity, and is directly 

 exposed to the elastic recoil of the lung. In this particular case, the 

 mercury in the manometer (M) is drawn toward the chest causing its ' 

 proximal limb to rise and its distal limb to fall until the negativity 

 in the thorax has been counterbalanced exactly. The manometer 

 therefore, measures, the traction which is brought to bear upon the 

 internal surface of the chest wall by the recoiling pulmonary tissue 

 and the force with which it opposes the pressure in the respiratory 



Fig, 235. — Diagram Illustrating the Manner of Insertion of a Cannula into 



THE Intrapleural Space. 

 T, trachea; L, lungs; H, heart; A, abd. cavity ;P, a probe is pushed through the inter- 

 costal space forcing the lung away from the chest wall and thus creating an artificial 

 space; M, the manometer then indicates the elastic pull of the lungs; S, stopcock to 

 prevent ingress of air before manometer is in place; K, kymograph for recording the 

 intrapleural pressure. 



passage. Hutchinson^ has attempted to measure the elastic force of 

 freshly excised human lungs by distending them with known amounts 

 of air. Upon these figures Heynsins^ bases his conclusion that the 

 intrapleural pressure during the static phase of the thorax amounts to 



— 4.5 mm. Hg. For dogs and rabbits the values of —3.9 mm. and 



— 2.5 mm. Hg respectively have been found. 



It must be evident that the term intrathoracic pressure indicates 

 the pressure prevailing elsewhere in the thoracic cavity outside the 

 pulmonary passage. Consequently, the terms intrapleural and intror 



1 Hermann's Handb. der Physiol., iv, 225 

 . 2 Pfluger's Archiv, xxix, 1882, 265. 



