METHODS OF MEASURING RESPIRATORY EXCHANGE 15 



Several improved models of this arrangement have been described in 

 later publications from the Nutrition Laboratory. 



When muscular movements and tone must be absolutely excluded 

 during a definite series of measurements the use of an anaesthetic or 

 of curari becomes necessary. Tangl has introduced the regular use 

 of curari for respiratory exchange purposes, and the results fully bear 

 out the importance of this step in improving the definition of conditions 



FIG. 2. The recording cage. After Benedict and Romans. " Amer. J. Physiol.," 28, 33. 



Recently Raeder [1915] has substituted a prolonged urethane nar- 

 cosis instead of curari for experiments on mammals. By putting off 

 the experiment proper until a number of hours after the narcotiza- 

 tion he obtains results of wonderful regularity. 



For ordinary experiments involving the determination of the 

 metabolism under "normal" conditions the rule initiated by Seegen 

 and Nowak [1879] : never to begin an experiment just after the intro- 



