178 RESPIRATION 



frequent sources of heart strain. They should be in- 

 dulged in but moderately and under medical advice, at 

 least until the heart is so far developed that its ability 

 safely to do work under conditions of strain has been 

 proved. 



As the perfection of the adjustment between circu- 

 lation and respiration is entirely automatic and beyond 

 the control of the will, the training necessary to attain 

 such perfection can only be gained by frequent active 

 work and exercise. For this reason, during the period of 

 growth and development, children should have much 

 physical activity, in order not only to perfect this con- 

 trol but also through it to attain full development of the 

 heart, lungs and blood-vessels. 



EXPERIMENTS AND DEMONSTRATIONS 

 Anatomy of the Respiratory Tract 



Materials: Sheep's lungs with wind-pipe and heart attached 

 (to prevent puncturing of lungs through careless removal of 

 heart) ; rabbit, cat, or rat; frog; normal salt solution; glass and 

 rubber tubing about ^ in. diameter, 12 in. long; some small 

 object, as a piece of cork or rubber ; microscope. 



1) Examine wind-pipe of sheep and trace its division into 

 bronchi. Notice in its wall rings of cartilage, so arranged that 

 dorsal aspect of tube (which lies against esophagus) has no 

 hard parts in it. 



2) Slip rubber tube on end of glass tube and insert other 

 end of glass tube into trachea; tie firmly; blow up lungs and 

 pinch rubber tube to keep distended. 



Note extensibility and elasticity of lungs ; their size and form 

 when distended; concavity of their lower (diaphragm) surface; 

 lobes; pleural membranes; and space occupied by heart. 



3) Trace one bronchus to its lung. 



a) Cut through lung tissue and follow branching bronchi. 

 Note cartilage rings, and lining mucous membrane. 



b) Wash surface of mucous membrane with normal salt 



