APPLICATIONS OF GAS ANALYSIS. 
VI. THE RESPIRATORY EXCHANGE AND INDIRECT 
. CALORIMETRY. 
_ By YANDELL HENDERSON. 
(From the Physiological Laboratory, Yale Medical School, New Haven.) 
(Received for publication, October 30, 1917.) 
The analysis of 10 cc. of expired air to determine its percentage 
of oxygen and COz is not appreciably more difficult than the de- 
termination of the nitrogen in 10 cc. of urine by the Kjeldahl 
method. The nitrogen found in the sample multiplied by the 
total volume of the urine from which it was taken gives us the 
nitrogen metabolism of the body. In the same way the oxygen 
(deficit) and the CO, found in the sample of expired air multi- 
plied by the total volume of the air expired in a given time 
afford the oxygen and carbon metabolism, and, by indirect 
calorimetry, the total energy exchange of the body. 
Certainly a knowledge of the oxygen, carbon, and energy ex- 
changes is quite as important in a wide range of problems as is 
the nitrogen exchange. Each should be equally a matter of 
routine in every well equipped biochemical and clinical labora- 
tory. In fact however the means and habit of determining 
nitrogen are universal, while determinations of the respiratory 
exchange are confined to a very few highly specialized laboratories. 
‘The reason for this anomaly lies in the fact that it is generally 
‘assumed that the elaborate and expensive apparatus of the 
“closed circuit’? method used by Benedict, Lusk, and their col- 
laborators is necessary. This is far from the truth. In fact, ina 
thorough comparative study and critique of all available methods 
Carpenter (1), although he does not say so explicitly, has shown 
implicitly that the (Tissot) “open circuit’ method of collecting 
the expired air in a graduated spirometer and analyzing a sample 
is equal in accuracy and superior in simplicity to the closed circuit 
method. r 
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