44 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



contents of the bag can be taken through a Haldane set of vessels for 

 absorbing water vapour and carbon dioxide and the total carbon di- 

 oxide determined by weighing. 



In the method of Zuntz and his colleagues (Geppert [1887], Magnus- 

 Levy [i 894]) the expired air is measured by passing through a gas meter 

 and an average sample taken for analysis (fig. 18). This method has 

 been used in a large number of researches of the highest importance 

 since it was published by Geppert and must therefore be described in 



FIG. 18. Gas meter, air sampling and analysing arrangement. After Zuntz. 

 Tigerstedt's " Handbuch," vol. i. 



some detail, though simpler and quite as effective arrangements are 

 now taking its place. 



The expired air is measured by passing through a gas meter which 

 it enters through (P). A narrow tube (L) leads from P to the gas 

 sampling tube (part of a Zuntz gas-analysis apparatus) filled with 

 mercury or acidulated water. As the gas meter revolves during 

 each expiration, the weight (F) is lowered correspondingly and with 

 it the tube (H) connected with the gas sampling tube. Some mercury 

 (or water) flows out from (J) and a corresponding quantity of the ex- 

 pired air is drawn into the sampling tube. The apparatus (R, D, G, E) 

 is a so-called thermo-barometer. 100 c.c. dry air at 760 mm. pressure 



