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EXPERIMENTAL PHYSIOLOGY 



Next, let the subject abstain from breathing (after an ordinary 

 expiration) for the space of half a minute, and record the respiratory 

 movements which succeed the abstention (dyspnoea). 



Lastly, allow the subject to respire a mixture of air and CO 2 

 (10 per cent.) contained in an oil-silk bag or a gasometer, and again 

 record the movements of the chest wall. 



FIG. 83. Prone-pressure method of artificial respiration. A, Pressure 

 being applied ; B, pressure removed. 



Measurement of tidal air passing into and out of lungs. Using 

 either an airtight mask or a mouth-tube provided with valves (in 

 this case the nostrils must be closed by a clip) allow the subject to 

 breathe during one minute into a carefully balanced spirometer (see 

 diagram, Fig. 82). Count the number of respirations in a given time, 

 and note the amount of air which has been breathed in that time. 

 From these results calculate the tidal air passing through the lungs 

 with each respiration. The observation should not be begun until the 

 subject is breathing regularly and unconsciously, and he must not be 

 permitted to see the movements of the spirometer. 



