138 



PEACTICAL PHYSIOLOGY 



beneath the tambour. Listen to the vesicular sounds with the binaural 

 stethoscope, and, by means of the key, signal the moment when the 

 sound begins and ends. Repeat the experiment for bronchial breathing, 



placing the stethoscope over the 

 7th cervical spine. Take a time 

 tracing with the seconds clock 

 beneath the respiratory tracing. 

 Count the pulse of the subject, 

 and determine the ratio of the 

 frequency of respiration to that of 

 the pulse. It is about 1 : 4. 



The Spirometer. The vital ca- 

 pacity is the greatest volume of 

 air that can be expired after the 

 deepest possible inspiration. The 

 tidal air is the volume of air 

 breathed at each respiration. 

 These measurements are made by 

 means of a spirometer. 



The spirometer is constructed as. 

 in Fig. 120. Open the tap, place 

 the spirometer at the mark 1000. 

 Then close the tap. Breathe in 

 and out through the mouthpiece, 

 holding the nose meanwhile. Di- 

 vert your thoughts, and let another 

 observe the volume of the 'tidal 

 air.' It will be about 200-250 c.c. 

 After breathing out the tidal air, 

 expire as deeply as possible. An additional 1500 to 2000 c.c. will 

 be expired. This is called the supplemental air. Breathe in as 

 deeply as possible. About 1500 to 2000 c.c. complemental air will 

 be inspired in addition to the tidal air. Place the spirometer at zero- 

 and take the deepest possible inspiration. Then make the deepest 

 possible expiration into the spirometer and thus measure the vital 

 capacity, i.e. tidal 250 c.c. + complemental 2000 c.c. + supplemental 

 2000 c.c. 



Fio. 120. Spirometer. T, Mouthpiece; M, 

 manometer ; Cp, counterpoise ; R, scale. 



