Chemical Changes in Animal Organism. 275 



volume of the air in the closed circuit, and this is made 

 good by the supply of fresh oxygen. This principle has 

 been adopted in an apparatus devised by Benedict which 

 can be employed for clinical purposes, the construction of 

 which is indicated in the accompanying diagram (Fig. 24). 



Fig. 24. 



A tension equalizer is placed in the circuit which serves 

 to keep the volume of the air constant. The amount of 

 oxygen consumed is ascertained by weighing the cylinder 

 of the gas in which it is contained at the beginning and 

 the end of the experiment. The subject of the experiment 

 breathes through a nose-piece into a wide metal tube 

 which forms part of the closed circuit, the mouth being 

 kept closed. 



The apparatus employed for the determination of the 

 gaseous exchanges is usually somewhat complex, and only 

 an indication of the principles employed has here been 

 attempted. A few words are necessary to indicate the 

 value of the results obtained by such determinations. If 

 the equation representing the complete combustion of 

 dextrose is given 



C 6 H 12 6 + 60 2 = 6H 2 + 6C0 2 

 it will be observed that the volume of oxygen consumed is 



