i66 



Life and Health 



In health the two pleural surfaces of the lungs are always 

 in contact, and they secrete just enough serous fluid to allow 



the surfaces to 

 glide smoothly 

 upon each other. 



252. Minute 

 Structure of the 

 Lungs. If one of 

 the smallest bron- 

 chial tubes be 

 traced in its tree- 

 like ramifications, 

 it will be found to 

 end in an irregular 

 funnel-shaped pas- 

 sage, wider than 

 itself. Around this 



FIG. 87. The Lungs, with the Trachea, Bronchi, 

 and larger Bronchial Tubes exposed, 

 terior view.) 



A, division of left bronchus to upper lobe ; , left 

 branch of the pulmonary artery ; C, left bronchus ; 

 Z>, left superior pulmonary vein ; , left inferior 

 pulmonary vein ; F, left auricle ; A", inferior vena 

 cava ; Z,, division of right bronchus to lower lobe ; 

 M } right inferior pulmonary vein ; IV, right supe- 

 rior pulmonary vein ; O, right branch of the pul- 

 monary artery ; P, division of right bronchus to 

 upper lobe ; R, left ventricle ; S, right ventricle. 



(POS . passage is grouped 

 a number of cavities 

 with honeycomb- 

 like walls, the air 

 cells, 1 or air sacs, of 

 the lungs. These 

 communicate freely 

 with the passage, 



and through it with 

 the bronchial branches, but have no other openings.* The 

 whole arrangement of passages and air sacs springing from 

 the end of a bronchial tube is called an ultimate lobule. 



1 The word " cell " is not used in this connection in its technical signifi- 

 cation of a histological unit of the body (sec. 16), but merely in its primary 

 sense of a small cavity. It is better, however, to call these cavities "air 



