108 



GENERAL ANALYSIS. 



394. WHEN THE BOX is ENLARGED the pressure of the 

 air, 15, is removed from the external surface of the Lung, 

 and the internal pressure of the air, 15, correspondingly 

 distends the Lung, overcoming its elasticity, 10; and 

 when the box is being restored to its former size the 

 external, 15, balancing the internal, 15, the elasticity, 10, 

 of the Lung as surely drives out the air, and the inner 

 surface of the box and the outer surface of the Lung will 

 be in the gentlest contact with each other all the while 

 that the box is enlarging and diminishing, and only by 

 closing the pipe leading into the Lung can the box be 

 made to press upon the Lung. 



395. EACH CHEST is such a box, most readily en- 

 larged and diminished by means of the muscles and car- 



FIG. 96. 



Fig. 9G 

 represents 

 the Hearts, 

 3, 4, be- 

 tween the 

 lungs, dis- 

 tended as in 

 life with the 

 front parts 

 cut away, to 

 show the di- 

 visions of 

 veins, arte- 

 ries,and 12, 

 the wind- 

 pipe ; 6,sys- 

 teinic arte- 

 ry; 7, sys- 

 ic vein ; 

 , 2, right 

 and left au- 

 ricles. 



394. What effect ? 895. What ? Describe Fig. 96. Is the Heart in the 

 centre of the chest ? 



