90 GENERAL SCIENCE 



to its normal position and forces air from the lungs by 

 reducing the size of the chest cavity. 



A conscious effort should be made occasionally to take 

 an increased amount of air into the lungs, " deep breath," 



since by so doing a larger portion of 



the lungs will be used. 



Experiment 25. Tie a rubber bag par- 

 tially filled with air to one end of a glass tube 

 and arrange the tube in a bell jar as shown in 

 Figure 89. A diaphragm for the bell jar may 

 be made by gluing a piece of leather with a 

 string through it to a piece of sheet rubber. 

 As the diaphragm is pulled down, the rubber 

 bag inside the bell jar will increase in size. 

 Why? Does it return to its former size when 

 the diaphragm is allowed to go back to its 

 FIG. 89. normal position? 



Mouth Breathing. - - The proper passage for the air 

 to the lungs in breathing is through the nose. When air 

 is inhaled through the nose, it is warmed before it reaches 

 the delicate tissues of the throat and lungs. The moist- 

 ened hairs of the nose also remove dust particles and 

 disease germs before they reach places where serious 

 injury may be done. 



The habit of mouth breathing is a bad one for a num- 

 ber of reasons, (a) The dust and germs are not removed 

 in the mouth as in the nose by the hairs and folds of 

 mucous membrane. (6) The air reaches the lungs before 

 it is properly warmed, (c) Mouth breathing hinders 

 the normal development of the upper jaw and destroys 

 the natural beauty of the face. 



With practice we can acquire the habit of nose breath- 

 ing even when exercising violently. Trainers of athletes 

 are careful to cultivate this habit, since mouth breathing 



