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RESPIRATION 



If the ear be placed in contact with the wall of the chest or be separated 

 from it only by a good conductor of sound or a stethoscope, a faint respiratory 

 murmur is heard during inspiration. This sound varies somewhat in dif- 

 ferent parts, being loudest or coarsest in the neighborhood of the trachea and 

 large bronchi (tracheal and bronchial breathing), and fading off into a faint 

 sighing as the ear is placed at a distance from these (vesicular breathing). 

 It is heard best in children. In them a faint murmur is heard in expiration 

 also. The cause of the vesicular murmur has received various explanations. 

 Most observers hold that the sound is produced in the glottis and larger 



FIG. 234. Tracing of the Normal Diaphragm Respirations of the Rabbit, a, With 

 quick movement of drum; b, with slow movement; /, inspiration; E, expiration. To be 

 read from left to right. (Marckwald.) 



bronchial tubes, but that it is modified in its passage to the pulmonary 

 alveoli. In disease of the lungs the vesicular murmur undergoes various 

 modifications, for a description of which one must consult text-books on 

 physical diagnosis. 



The Quantity of Air Breathed. Tidal air is the quantity of air 

 which is habitually and almost uniformly changed in each act of breathing. 

 In a healthy adult man it is about 30 cubic inches, or about 500 c.c. or half 

 a liter. In college students the tidal air is somewhat less, varying from 300 

 to 400 c.c. 



The complemental air is the quantity of air which can be drawn into the 

 lungs by the deepest inspiration over and above that which is in the lungs 

 at the end of an ordinary inspiration. Its amount varies, but may be reck- 

 oned as 100 cubic inches, or about 1,600 c.c. 



