VITAL CAPACITIES 



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respiration, and the average number of respirations per minute, determined 

 in experiment i, calculate the amount of air breathed per hour and per day. 

 5. Vital Capacities. Using the spirometer as in the preceding 

 experiment, set the instrument at zero and exhale into it: a, Begin with the 

 fullest possible inspiration and exhale the greatest possible amount of air 

 from the lungs. This is known as the vital capacity. 



b, Beginning at the end of an ordinary expiration exhale into the instru- 

 ment the greatest possible amount. This is called the reserve air. 



c, Following ordinary inspiration exhale into the instrument until you 

 reach the ordinary state of expiration. This involves the conscious fixing 

 of two points in the respiratory act, namely, the summit of inspiration and 

 expiration, which are ordinarily automatically adjusted by the body. The 

 error of the determination is therefore great. It is better to make this measure- 

 ment in sets of ten, as in the preceding experiment, and take the average. 



FIG. 243. The Chest Pantograph for Recording the Outlines of the Chest. The fixed point 

 in the instrument is /; the points a, b, x, y, are movable joints; when point t is made to trace 

 the outline of the chest, point r will give a corresponding movement and can be made to trace this 

 movement on recording paper. (Hall.) 



This reduces the error. This quantity of air is known as the tidal air. One 

 can measure the tidal air and the reserve air together, check them against 

 the sum of the tw r o, as in a and b separately. 



The sum of the tidal and reserve air taken from the vital air will leave 

 the amount which one may inspire over and above that in the chest at the end 

 of ordinary inspiration. This is called complemental. The complemental 

 can be measured by inspiring the air from the spirometer, but this is not 

 good hygiene where large numbers are using the same instrument, unless 

 the instrument be thoroughly cleaned before the inspiration is taken. 



6. The Respiratory Pressure in Man. Measure the respiratory 

 pressure, the pressure of the air in the air- passages, by means of the mercury 

 manometer, or by a graduated Marey's tambour. Connect the piece of 



