190 THE MECHANISM OF 



a definite movement. In the normal mixed inspiration, where 

 diaphragm and ribs co-operate equally or almost equally, the 

 lung expands in three directions downwards, forwards, and out- 

 wards, the root sharing in the combined movements. When the 

 abdominal breathing is well marked, the trachea can be felt de- 

 scending in the neck as the epigastrium comes forwards. By the 

 use of X-rays the heart, and therefore the roots of the lungs, for 

 the heart is bound firmly to them, can be seen to follow the move- 

 ments of the chest wall ; with a thoracic breath, the heart follows 

 the movement of the sternum ; with a diaphragmatic breath, it 

 descends with the diaphragm. The great muscular crura of the 

 diaphragm, forming one-third of that muscle, can act directly on 

 the roots of the lung through the pericardium and heart. In cases 

 where the roots of the lungs are bound to the posterior or stationary 

 wall of the thorax through adhesions set up by mediastinitis, 

 Wenckebach observed that both the respiratory and circulatory 

 movements were abnormal in character. 



It is usually said that the division of the lungs into lobes has 

 no functional significance. This opinion is founded on the fact 

 that they may be only partially developed or completely oblite- 

 rated by disease without altering the functional capacity of the 

 lung. The obliteration of the pleural cavity by adhesions has so 

 little apparent effect on the respiratory movements that their 

 presence cannot be detected during life. In one case, where 

 the lungs were completely adherent, Hutchinson found the vital 

 capacity to be 680 cc. above the average amount. This method 

 of reasoning is liable to lead one into great error, for there are 

 many functional organs in the body which may be removed with- 

 out any marked disturbance of the bodily economy. When the 

 normal respiratory movements of the lung are fully understood 

 it will be found that the great fissure, which divides the upper 

 from the lower lobe, is functional in its significance. The upper 

 lobe is normally expanded by one mechanism, the lower by 

 another. When the lung is removed from the body and slightly 

 inflated there will be seen marked out on the lateral and anterior 

 aspects of the upper lobe especially in the lungs of women 



