CHAPTER VIII. 

 RESPIRATION. 



Object. The object of respiration is to furnish oxygen to 

 the tissues and remove carbon dioxide from them. The in- 

 tervention of the lungs and blood is necessary to accom- 

 plish this end. At each inspiration a certain volume of air 

 is taken into the lungs, and from it, while in these organs, is 

 removed a certain amount of oxygen which enters the blood 

 of the pulmonary capillaries. At each expiration there is re- 

 moved from the lungs a certain volume of air, and it con- 

 tains a proportion of carbon dioxide over and above that 

 contained in the ordinary atmosphere, i. e., in the inspired 

 air ; this carbon dioxide is removed from the blood of the pul- 

 monary capillaries and enters the air in the lungs. The en- 

 trance and exit of air to and from the lungs, in obedience to 

 movements to be noticed later, constitutes what is commonly 

 called respiration; but the mere tide of the air inward and 

 outward is of no significance unless the interchange of oxy- 

 gen and carbon dioxide takes place. 



Internal Respiration. Nor is this interchange of value 

 unless another occurs in the tissues. The oxygen which has 

 entered the pulmonary blood is conveyed by the circulation 

 to a point where the fluid is brought into very close relation- 

 ship with the tissues (namely, in the capillaries), and is here 

 given up to the cells; furthermore, at. the same place the 

 cells give up carbon dioxide to the capillary blood. It is only 

 for the purpose of effecting this last interchange that there 

 is any respiration, or any respiratory apparatus. Inspira- 

 tion and expiration, the pulmonary interchange of gases, the 

 transportation of oxygen and carbon dioxide to and away 

 from the. cells, are all equally immaterial except as being 

 means to the accomplishment of this end. It would make no 

 difference whether pulmonary respiration were kept up or 



