100 



THE VITAL PROCESSES 



the thoracic space, air is made to pass between the outside 

 atmosphere and the interior of the lungs. Finding its 

 way into the smallest divisions of the lungs, called the 

 alveoli, the air comes very near a large surface of blood. 

 By this means the carbon dioxide diffuses out of the 

 blood, and the free oxygen enters. Through the com- 

 bined action of the organs of respiration and the organs 



that move the blood and the 

 lymph, the cells in all parts of 

 the body are enabled to exchange 

 certain gaseous materials with 

 the outside atmosphere. 



FIG. 49. Model for demonstrat- 

 ing the lungs. 



Exercises. I. How does air en- 

 tering the lungs differ in composition 

 from air leaving the lungs ? What 

 purposes of respiration are indicated by 

 these differences ? 



2. Name the divisions of the lungs. 



3. Trace air from the outside at- 

 mosphere into the alveoli. Trace the blood from the right ventricle to 

 the alveoli and back again to the left auricle. 



4. How does the movement of air into and from the lungs differ 

 from that of the blood through the lungs with respect to (a) the direc- 

 tion of the motion. (<) the causes of the motion, and (V) the tubes 

 through which the motion takes place ? 



5. How are the air passages kept clean and open ? 



6. Describe the pleura. Into what divisions does it separate the 

 thoracic cavity ? 



7. Describe and name uses of the diaphragm. 



8. If 30 cubic inches of air are passed into the lungs at each 

 inspiration and .05 of this is retained as oxygen, calculate the number 

 of cubic feet of oxygen consumed each day, if the number of inspira- 

 tions be 1 8 per minute. 



9. Find the weight of a day's supply of oxygen, as found in the 

 above problem, allowing 1.3 ounces as the weight of a cubic foot. 



10. Make a study of the hygienic ventilation of the schoolroom. 



