TECHNIQUE FOR METABOLISM DURING REST. 117 



The ratios found for the several disks are as follows: 16-min. disk, 21.21 

 per cent of air passing through absorbers; 22-mm. disk, 14.37 per cent; 

 29-mm. disk, 10.00 per cent; 40-nim. disk, 5.60 per cent; 60-nun. disk, 

 2.54 per cent. The ratio for the main discharge opening (97 mm.) 

 was 1.14 per cent. 



The carbon-dioxide tests with the subsidiary chamber were primarily 

 made to estabhsh the several factors. They were then in a sense re- 

 versed in that the factors thus established were employed in determin- 

 ing the known amounts of carbon dioxide admitted into the large 

 respiration chamber; the agreement of these checks is all that could be 

 desired. 



RESIDUAL ANALYSIS. 



In observations on domestic animals, or with a group of men, ex- 

 tending over a considerable period of time, small changes in the actual 

 amount of carbon-dioxide residual in the chamber at any given time 

 are practically without influence upon the final results. When, how- 

 ever, the experimental period is shortened to such an extent that vari- 

 ations in the residual amount inside the chamber may become a meas- 

 urable proportion of the total amount withdrawn during the period, 

 the necessity of a careful determination of the residual amounts is 

 obvious. This feature of the apparatus, which plays no role in experi- 

 menting with domesticated animals when long experimental periods 

 are employed, requires the use of a gas-analysis apparatus for short 

 experimental periods with humans. Practically all of our work was 

 carried out by using a Sonden-Pettersson gas-analysis apparatus,^ 

 which made it possible to determine the carbon dioxide to approxi- 

 mately 0.001 per cent. Since the total volume of the chamber was not 

 far from 44,000 liters, it will be seen that each one thousandth of 1 per 

 cent carbon dioxide corresponded, roughly speaking, to 0.9 gram of 

 carbon dioxide; hence the accuracy was all that could be desired. 



In the latter part of our experimenting during the season of 1917-18 

 we were much attracted by the accuracy of the small Haldane appa- 

 ratus for carbon dioxide alone.^ This gives an accuracy for carbon- 

 dioxide measurements that for the great majority of experiments is 

 perfectly satisfactory. The apparatus is simple, relatively easy to 

 manipulate, very rapid, sufficiently compact to be portable and has 

 none of the fragile parts so essential to the Sonden apparatus. Our 

 experience with the various types of Pettersson apparatus which have 

 been put upon the market has been upon the whole rather unsatis- 

 factory. 



While in the large majority of our observations on Squad A, correc- 

 tions for the residual air were not only unnecessary but at times, owing 

 to errors of gas analysis, positively disadvantageous, we have in practi- 



1 Benedict, Carnegie Inst. Wash. Pub. No. 166, 1912. 



2 Haldane, Methods of air analysis, 1912, p. 62. 



