CHAPTER XVI. 

 THE OBJECT AND THE MECHANICS OF RESPIRATION. 



The Object of Respiration. Blood is renewed, so far as 

 ordinary food materials are concerned, by substances either 

 directly absorbed by the blood-vessels of the alimentary 

 canal, or taken up by the lymphatics of the digestive tract 

 and afterwards poured into the blood. But in order that 

 energy may be set free for use by the tissues of the body 

 (Chap. VIII.), oxidations must occur, and the continuance 

 of these vital oxidations depends on a constant supply of 

 oxygen. As their result, waste substances are produced, 

 which are no longer of use to the body, but detrimental to 

 it if present in large quantity. The most abundant of 

 these wastes is carbon dioxide gas. 



The function of respiration has for its objects (1) to 

 renew the supply of oxygen in the blood, and (2) to get rid 

 of the carbon dioxide produced in the different organs. 



The Respiratory Apparatus. This consists primarily of 

 two elastic bags, the lungs, placed in the thorax, filled with 

 air, and communicating by the air-passages with the sur- 



How is the blood renewed as regards ordinary food matters? 

 What must occur that energy be set free for use by the body ? What 

 is necessary that the oxidations may continue? What do the oxida- 

 tions produce? Which is the most abundant waste substance of the 

 body? 



What are the objects of respiration ? 



Qf what does the respiratory apparatus primarily consist ? 



