280 



RESPIRATION 



gas tubing with the proximal limb of the mercury manometer and provide 

 it with a glass mouthpiece. Insert this mouthpiece well back into the 

 cavity of the mouth, closing the lips firmly about it, leaving the pharyngeal 

 muscles relaxed. Note the variations in pressure at the height of ordinary 

 inspiration and expiration, with the nasal passages open. Repeat with 

 forced inspiration and expiration, close the nasal passages, and make the 

 maximal expiratory and inspiratory effort. The manometer may be ad- 

 justed to write on the smoked paper, or one may read the variations directly 

 from the manometer schedule, in which case it facilitates the reading if one 

 clamps the rubber tube at the moment the reading is desired. 



7. Demonstration of Carbon Dioxide in Expired Air. Arrange 

 two flasks, as in figure 244, filling each one-third full of baryta water, or 



FIG. 244. Apparatus for Demonstrating Excess of CO 2 in Expired Air. Flasks filled with 



lime-water. 



lime-water. Close the lips around the mouthpiece of the apparatus and 

 inhale and exhale the air through it; close the nostrils if necessary. The 

 inspired air will come through a, the expired air out through b. The baryta 

 water in b will quietly become clouded with a white precipitate, while that 

 in a will remain clear or only very slightly clouded, showing the excess of 

 carbon dioxide in expired air. 



8. Quantitative Determination of Carbon Dioxide and Oxygen in 

 Inspired Air and in Expired Air, by HempePs Method. Inspired 

 Air. Fill a gas buret, see figure 236, with water and close the pinch- 

 cock. Fill it with air taken outside the laboratory. Measure the vol- 

 ume of gas contained at the ordinary temperature and barometric pressure 

 of the laboratory. Connect with a potash pipet, drive the air over into the 

 bulb of the pipet, shake it up until all the carbon dioxide is absorbed. Draw 

 the air back into the buret and measure. The amount of carbon dioxide 

 in the external air is usually so small that it is difficult to measure by this 

 method. Now connect the buret with a pipet containing pyrogallic acid, 

 run the air over into the pyrogallic-acid bulb and shake up thoroughly until 

 no further excess is absorbed, then remeasure the excess in the buret. The 

 loss in volume is due to the absorption of oxygen; the air remaining in the 



