580 



METABOLISM 



The growing importance in clinical investigations of measurements of 

 the respiratory exchange and the necessity for having methods that are as 

 simple as is consistent with accuracy, have led to the introduction of 

 several other forms of apparatus, of which those of F. G. Benedict and of 

 Tissot are the most important. In these methods no calorimeter is em- 

 ployed but the energy exchange is calculated from the amount of 2 

 inspired in a given time. In Benedict's method a tightly fitting mask is 

 applied over the nose and mouth and connected, by a short T-piece, with 

 the same tubing as that used in the respiration calorimeter. The patient 



Fig. 176. Diagram of Atwater-Benedict respiration calorimeter. As the animal uses up the Q z , 

 the total volume of air shrinks. This shrinkage is indicated by the meter, and a corresponding 

 amount of O 2 is delivered from the weighed O 2 -cylinder. The increase in weight of bottles 

 II and III gives the CO 2 ; that of I, the water vapor. 



thus breathes in and out of the air stream that is passing along the tubing 

 without any of the obstruction experienced when the breathing has to be 

 performed through valves, as in the older (Zuntz) forms of portable 

 respiratory apparatus. It is particularly for studies on man that this 

 apparatus has been devised. The Tissot and Douglas methods are de- 

 scribed in Chapter LXIV, where the method used for calculating the re- 

 sults is also outlined. 



This is called the method of indirect calorimetry, and it has been clearly 

 established by numerous observations that the results agree exactly with 

 those secured by the method of direct calorimetry described above. For 



