22O RESPIRATION. 



i 



consumption. A like process occurs in the blood itself, 

 independently of the decay of the tissues; for on the 

 continuance of such chemical processes depend, directly 

 or indirectly, not only the temperature of the body, but 

 all the forces, the nervous, the muscular, and others, 

 manifested by the living organism. 



The venous blood, containing the new-formed carbonic 

 acid, returns to the lungs, where a portion of the carbonic 

 acid is exhaled, and a fresh supply of oxygen is again 

 taken in. 



Mechanism of Various Respiratory Actions. 



It will be well here, perhaps, to explain some respiratory 

 acts, which appear at first sight somewhat complicated, 

 but cease to be so when the mechanism by which they 

 are performed is clearly understood. The accompanying 

 diagram (fig. 65) shows that the cavity of the chest is 

 separated from that of the abdomen by the diaphragm, 

 which, when acting, will lessen its curve, and thus de- 

 scending, will push downwards and forwards the abdominal 

 viscera; while the abdominal muscles have the opposite 

 effect, and in acting will push the viscera upwards and 

 backward, and with them the diaphragm, supposing its 

 ascent to be not from any cause interfered with. From 

 the same diagram it will be seen that the lungs communi- 

 cate with the exterior of the body through the glottis, and 

 further on through the mouth and nostrils through 

 either of them separately, or through both at the same 

 time, according to the position of the soft palate. The 

 stomach communicates with the exterior of the body 

 through the oesophagus, pharynx, and mouth; while 

 below, the rectum opens at the anus, and the bladder 

 through the urethra. All these openings, through which 

 the hollow viscera communicate with the exterior of the 

 body, are guarded by muscles, called sphincters, which can 



