HOW WE BREATHE 



153 



INSPIRATION 



SUMMAEY. 



External intercostal! contract. 



Raise the ribs. 

 Chest enlarged Make the chest wider. 

 Diaphragm depressed. 

 V. Chest made deeper. 

 Lungs expand with the chest. 



Air rushes in through the trachea, rilling the en- 

 larged lungs. 



( Elastic -walls of the thorax recoil. 

 Elastic lungs recoil. 

 Internal inter cost als con--, 



tract. 



Ribs depressed. 

 Chest becomes nar- 



Forced 

 -expira- 

 tion. 



Chest made I rower, 

 smaller | Diaphragm raised. 



Chest made shallower. 

 Abdominal muscles con- 

 EXPIRATION . . \ tract. 



Abdominal organs press 

 on under side of dia- 

 phragm. 

 \ Air forced out through the trachea. 



QUESTIONS ON LESSON XXVI. 



1. Describe the structure of the walls of the chest. 



2. Describe the arrangement of the organs of the thorax, and the arrange- 



ment and nature of the membranes which surround the lungs. 



3. What would be the effect of an opening through the wall of the chest ? 



Explain the cause. 



4. Would it be possible for a person to breathe while the wall of the chest is 



perforated ? Give reasons for your answer. 



5. How do the walls of the chest move during respiration ? 



6. In what way do the ribs move ? By what mechanism are they moved ? 



7. How does the contraction of the diaphragm produce inspiration ? 



8. Through what passages does the air move in breathing ? 



9. Describe fully the manner in which the intercostal muscles move the ribs. 



10. What are the forces which expel the air from the lungs in expiration ? 



1 1 . Describe the course of the air and the movements which take place 



during coughing, sneezing, and sniffing. 



12. What is a sigh ? How does it differ from an ordinary inspiration? 



LESSON XXVII. 

 THE LIVER. 



The liver is the largest gland in the body. In the adult it weighs 

 from 50 to 60 ounces, and forms about one-fortieth the weight of 

 the entire body. 



It is situated at the top of the abdomen, with its upper and 



