140 THE HUMAN HODY. 



QUESTIONS. 



SECTION I. 1. What is respiration ? 



2, What would air look like if we could see it? 



3, Is air a material substance? What is it composed of? 

 4 What is the use of the nitrogen in the air ? 



5, What is the use of carbonic-acid gas in the air? Does man 

 use it ? What is adding constantly to the carbonic-acid gas in the 

 air? What is adding constantly to the oxygen in the air? 



6, Name some characteristics of oxygen. 



SECTION II. 1. Does all of the air which we breathe in enter 

 the blood? 



2, What are the lungs? How does the oxygen pass through 

 them into the blood-vessels? 



3, How do frogs breathe under water? 



4, How do fishes breathe? 



5, In what are all breathing-organs alike ? 



6, Illustrate the structure of a human lung by a bunch of grapes. 



7, Illustrate the structure of a lung by a tree. 



8, Can this structure be seen with the naked eye? 



SECTION III. 1. Name the passages by which the air reaches 

 the lungs. 



2. What two parts does the nose consist of? With what other 

 cavities are the cavities of the nose connected? 



3, 4. Where are the nerves of smell, and how do the odorous 

 particles reach them? 



6. Give three reasons for breathing through the nose rather than 

 the mouth. 



6, What is a safeguard against taking cold when going from a 

 heated room into cold air? 



7. Where do the air-passage and the food-passage cross each 

 other? Why does not food enter the windpipe? 



8. What is the larynx? 



9, Describe the trachea. 



10, Into what does the trachea divide ? 



11. Describe the course and termination of the bronchial tubes. 



SECTION IV. 1. Does air enter the lungs of itself? 



2, What movements can we see when we watch a person breath- 



