External Respiration. 97 



2. Bending the rib cartilages and lifting the chest. 



3. Stretching the lungs. 



Elastic Reactions of Expiration. 



1 . Elastic reaction of the abdominal walls and contents. 



2. Elastic reaction of the rib cartilages. 



3. Elastic reaction of the lungs. 



Forced Respiration. Thus far we have been speaking 

 of ordinary respiration. In forced respiration, as in shout- 

 ing, many muscles are brought into play to expel the air 

 rapidly and forcibly. In such an act as coughing there is 

 vigorous action of the abdominal muscles. 



Abdominal and Thoracic Respiration. The main part of 

 respiration is performed by the diaphragm, and is there- 

 fore called diaphragmatic or abdominal breathing. Breath- 

 ing by means of the chest walls is called thoracic, or costal 

 breathing. 



The Rate of Respiration. Adults breathe about seven- 

 teen or eighteen times a minute, or about one breath to 

 four heart beats. The rate is increased by exercise, tem- 

 perature, digestion, excitement, age, etc. 



Special Forms of Breathing. Coughing is a forcible 

 expiration, usually directed through the mouth, and for the 

 purpose of getting rid of some irritating substance. In 

 sneezing there is first a deep inspiration, and then the air 

 is forced out, chiefly through the nose. Sneezing may be 

 prevented by pressing firmly on the upper lip. Hiccuping 

 is sudden inspiration, produced by a jerky action of the 

 diaphragm, accompanied by a sudden closing of the en- 

 trance to the windpipe. In case of choking it is well to 

 hold the head well forward, and perhaps downward. A 

 smart slap between the shoulders sometimes helps dislodge 



