APPARATUS AND METHODS USED IN THIS RESEARCH. 65 



quotient for the whole sojourn inside the chamber as an index of the 

 character of the combustion. It is thus perfectly logical to compute 

 the indirect calorimetry from the measurements of the carbon dioxide 

 and the calorific value of carbon dioxide for the particular respiratory 

 quotient determined at the time. 



This is the exact reverse of the method employed by Zuntz, who 

 measures the oxygen consumption with great accuracy and computes 

 the heat-output by indirect calorimetry, using the calorific value of 

 oxygen with the various respiratory quotients. Theoretically either 

 method gives reliable results and is without criticism. On the other 

 hand, in experiments made with the respiration chamber, a rapid 

 change in the value of the respiratory quotient is always possible. 

 This is particularly true after feeding, since there may be a considerable 

 rise in the respiratory quotient immediately after the food is taken, 

 followed by a relatively rapid fall, thus materially affecting the indirect 

 determination of the heat-output. Strictly speaking, therefore, the 

 respiratory quotient should be determined for each individual period. 

 As a matter of fact, in observations made a considerable time after the 

 food had been taken, the respiratory quotient would remain relatively 

 constant throughout the whole period of an hour or an hour and a half. 

 In most of our observations the measurements of oxygen did not begin 

 until some time after food was taken, and the preliminary period is not 

 considered in our discussion of the respiratory quotient. While a 

 gradual falling of the quotient would be expected as the time increased 

 after food was taken, we have every reason to believe that, with the 

 conditions obtaining in our observations, the actual fall in the quotient 

 was very slight and could but rarely, if at all, affect the calculation of 

 the indirect calorimetry. In this series of observations we have com- 

 puted the indirect calorimetry from the direct measurements of the 

 carbon dioxide, using the calorific values of carbon dioxide 1 for the 

 respiratory quotients obtained during the experimental period. 



The fact should again be emphasized here that tests for tightness 

 and efficiency preceded every individual observation and check tests 

 for determining the respiratory quotient with alcohol were made once 

 a week. 



The later method for determining the absolute amount of alcohol 

 burned and the respiratory quotients for short periods approximating 

 the periods of observation with infants was not perfected until the 

 fall of 1913; nevertheless we feel confident that the number of control 

 tests made with the older method in connection with these researches 

 is fully justified in order to secure absolute accuracy in this, the first 

 extensive use of the apparatus for studying infant metabolism. 



^ee table 15, p. 29. 



