

RESPIRATION. 



diaphragm descends, and thus the cavity of the chest is en- 

 larged in every direction. This expansion, like that of a 

 bellows, causes a vacuum, and as the lungs are passive, the 

 air consequently rushes in through the mouth and nostrils 

 to fill it, and this influx of air continues until the density of 

 the internal, is equal to that of the external air, when the 

 act of inspiration is at an end. Again, the intercostal 

 muscles relax, and the ribs, by their elasticity, are restored 

 to their natural position, while, at the same moment, the dia- 

 phragm relaxes, and allows the abdominal muscles to con- 

 tract and thrust it up into the chest. Thus the lungs being 

 pressed upon in every direction, below by the diaphragm, 

 before by the sternum and ribs, and behind by the spine and 

 ribs, the air within them is pressed out! Such is the beau- 

 tiful and complicated mechanism of respiration. 



Fig. 8. 



The cut upon the left represents the natural shape of the chest, and 

 that upon the right, the contracted state of it, owing to tight lacing. 



16. Now we can easily understand how tight-lacing alters 

 the shape and diminishes the capacity of the chest. By 

 looking at the cut, we see that the figure of the chest is that 

 of an irregular cone, with a convex projection on each side, 

 and flattened before and behind. I By compressing it, how. 

 ever, by corsets, it is changed into' a cylinder, its lower part 

 being forced in, so that its transverse diameter is diminished 



