Respiration 



341 



with the nose, pharynx, larynx, trachea, and bronchial tubes, or 

 bronchi, make up the respiratory system of man. 



The Diaphragm and the Ribs. The diaphragm is a dome- 

 shaped muscle attached to the ribs. It forms the floor of the 

 chest. When the diaphragm 

 contracts it flattens and thus 

 deepens the chest. At the same 

 time the muscles connected with 

 the ribs contract, pulling them 

 outward and upward, thus 

 broadening the chest. The air 

 then rushes into the lungs. This 

 action is called inspiration. The 

 return of the muscles to their 

 former position lessens the ca- 

 pacity of the chest, and forces 

 the air from the lungs. This 

 is called expiration. TuBES AND AlR SACS OF THE LuNGS 



The Lungs. The lungs are two sponge-like organs com- 

 posed of minute air tubes, air sacs, and capillaries. They are 

 located in the chest and are protected by the ribs and the breast 

 bone. Each lung is covered with a membrane called the pleura, 

 which also lines the chest cavity. 



Red Corpuscles. The blood is composed of red and of white 

 corpuscles floating in a liquid called plasma. The red corpuscles 



are exceedingly small cells 

 consisting largely of a sub- 

 stance called hemoglobin. This 

 substance is the important 

 part of these corpuscles be- 

 cause it contains iron which 

 has a strong attraction for 

 oxygen with which it unites 

 readily. When the blood cir- 

 culates through the lungs, the 



BLOOD CORPUSCLES 



red corpuscles take up oxygen from the air in the lungs and 

 rapidly convey it to the cells in all parts of the body. The 



