132 RESPIRATION 



no difference whether pulmonary respiration were kept up or not 

 if oxygen could be introduced into the blood and carbon dioxide 

 removed from it in some other equally efficient way. So far as 

 the cell is dependent on the acquisition of oxygen and the re- 

 moval of carbon dioxide, it would make no difference if there 

 were no respiration and no circulation if these materials could 

 be acquired and removed in some other equally efficient way. 



On the other hand, it were useless to keep up artificial respira- 

 tion or to inject oxygen into the lungs if the cells, through some 

 disability, cannot take up the oxygen furnished, or if the circu- 

 lation cannot absorb or convey the oxygen. 



It is seen that, from the standpoint of the blood, the interchange 

 of gases in the lungs is exactly opposite to that in the tissues; 

 that is to say, in the lungs it loses carbon dioxide and gains oxygen, 

 while in the tissues it loses oxygen and gains carbon dioxide. 

 The pulmonary interchange is properly termed external res- 

 piration in contradistinction to that in the tissues which is 

 termed internal respiration. 



It is needless to comment upon the universal necessity of oxy- 

 gen to the life of cells. Its appropriation is to be looked upon 

 as a part of the nutritive process; and, indeed, while in the long 

 run, cells are certainly dependent upon the nutriment furnished 

 by the ordinary aliments, they will retain their vital activity for 

 a longer time when deprived of any or all of these than when 

 deprived of oxygen alone. This gas is more immediately 

 necessary to the maintenance of life than is any other substance. 



Since, in order to bring about internal respiration in the human 

 being, the lungs and circulation happen to be necessary, attention 

 will have to be directed to the respiratory phenomena taking 

 place in both. 



ANATOMY OF THE RESPIRATORY ORGANS. 



It will be considered that the air has passed through the pos- 

 terior nares into the pharynx and is ready to enter the larynx. 



