NORMAL PROCESSES OF ENERGY METABOLISM 525 



sure and temperature changes a compensating device in the form of a 

 spirometer is inserted (see Figs. 7 and 8). 



The approximate amount of water vapor coming from the subject's 

 hody and the amount of carbon dioxid exhaled from his lungs is found 

 by direct weighing of the absorbers. Likewise weighing of the oxygen 

 cylinder gives within a small margin the amount of oxygen absorbed by 

 the subject. These amounts would be absolutely correct if there were no 

 change in barometric pressure or temperature of the confined air, and if 

 the composition of the air at the end of an observation period were exactly 

 the same as at the beginning. 



Barometric pressure and temperature are readily determined from ac- 

 curate instruments and corresponding corrections in the volume of the 

 contained air are readily made. For detecting alterations in the composi- 

 tion of the air resulting from inefficiency of an absorber or from unusual 

 production of COj or water vapor, known volumes of the circulating cur- 

 rent are diverted from the main pipe and are made to pass through a 

 smaller channel over sulphuric acid and soda lime and sulphuric acid again 

 (exactly as in the main circuit) contained in TJ tubes which can be weighed 

 to a high accuracy on a sensitive balance (Fig. 8). 



As an illustration of a compact form of this apparatus constructed for 

 determination of the respiratory exchange alone (without direct measure- 

 ment of the heat) either in laboratory animals or in infants, the design 

 of Benedict and Talbot may be described. 



This apparatus was originally described by the authors in a preliminary 

 publication in 1912. Later it was somewhat modified and was employed 

 in most of their observations on the infant in the form shown in Fig. 7. 

 In this form it was capable of determining the oxygen directly, exactly on 

 the same principle as that described above for the respiration calorimeter. 



The chamber C, in which the infant reposes, is provided with a water 

 jacket, W. W. for temperature control. The air leaves the chamber (Fig. 

 7) near the right hand end at O, and is drawn by the rotary blower over a 

 wet and dry bulb psychrometer, Z, which gives the amount of moisture in 

 the air of the chamber. A can, 1ST, filled with dry cotton batting is also 

 placed in the air-current between the blower and the chamber to act as a 

 muffler. After leaving the exhaust side of the blower, P, the air is forced 

 through an empty glass bottle, A, which serves as a trap should any back- 

 pressure take place and sulphuric acid be forced back from the water-ab- 

 sorbing vessels, B and C. These latter vessels are of peculiar construction. 

 They were designed by Williams for the small respiration calorimeter at 

 Cornell Medical College. The air passes along a pipe to a 2-way valve, V, 

 where it may be deflected through either of the soda lime bottles D t or D 2 

 in which the carbon dioxid is absorbed. Since the reagent must be some- 

 what moist to facilitate the absorption it gives up water-vapor to the dry 

 air-current, which must in time be absorbed by suh nuric acid in the Wil- 



