THE INDIVIDUAL GROUPS OF PROTEINS 515 



(2) Expired Air. 



A balloon of thick gold beater's skin from 50-100 litres in capacity is 

 emptied by rolling it up to a scroll. It is then rinsed out with expired air 

 by blowing into it and again rolling it up. It is half-filled with expired air 

 by making a number of steady normal expirations into it, the inspired air 

 being taken in through the nose, or the inspired and expired air may be 

 separated by valves attached to an anaesthetic mask fitting over the mouth 

 and nose. A sample of the well- mixed expired air is drawn off from the 

 centre of the bag by a long glass tube which has been filled with expired air 

 just previously. The gas in the sample tube is drawn into the gas burette 

 of the apparatus, measured and analysed for carbon dioxide and oxygen. 



If the volume of expired air and the time taken to collect it have been 

 measured, the gaseous exchange per minute can be calculated. 



(3) Alveolar Air. 



Alveolar air is collected most easily by the method of Haldane and 

 Priestley : 



A piece of canvas-lined hosepipe 4 feet long and i inch in diameter 

 is fitted with a glass tube as mouthpiece, '75 to i inch in diameter, to which 

 is attached a side tube of narrow bore (1-2 mm.). The gas burette of the 

 analysis apparatus is fastened to the side tube by a piece of stout india- 

 rubber tubing. The levelling tube of the burette is placed at such a level 

 that the burette can be half-filled with the alveolar air when the tap is opened. 



The subject breathes quietly and at the end of a normal inspiration 

 applies his mouth to the mouthpiece and makes a very rapid and complete 

 forced expiration. At the end he closes the mouthpiece with his tongue 

 and at the same time opens the tap of the gas burette so that alveolar air (i.e. 

 supplemental air) is drawn into it and fills this space. The tap is closed 

 ind the levelling tube placed so that the mercury in the gas burette will fall 

 to the lowest graduation when the tap is open. The subject again breathes 

 quietly and steadily for some time; at the end of a normal expiration he 

 makes a second complete and forced expiration through the tube, closes the 

 mouthpiece with his tongue and opens the tap of the gas burette. The alveolar 

 air is drawn in and fills the burette. The mixture of the two samples of alveolar 

 air will have a composition intermediate between that at inspiration and ex- 

 piration. The gas is analysed. The single analysis carried out in this way 

 obviates the necessity of performing two analyses and taking the mean. 



In the same way the composition of alveolar air (a) after taking 20 deep 

 rapid breaths, (b) after holding the breath for 30 seconds and (c) immediately 

 after severe exercise can be determined. 



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