QUANTITY OF AIR BREATHED 



259 



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 different 

 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 



Tambour. 

 Ivory button. 



Tube to commu- 

 nicate with re- 

 cording tam- 

 bour, 



Ball to fill appa- 

 ratus -With air. 



FIG. 233. Stethometer. (Burdon- Sanderson.) 



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

 tubes, but that it is modified in its passage to the pulmonary alveoli. In 

 disease of the lungs the vesicular murmur undergoes various modifica- 

 tions, 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 draw r n into the 

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



