TECHNIQUE FOR METABOLISM DURING REST. 85 



bottle, C, where the water-vapor from the lungs is removed. It then 

 passes through a soda-lime bottle, D, in which the carbon dioxide is 

 absorbed, and next to a second calcium-chloride bottle, E, where the 

 water vapor from the soda hme is absorbed. The air, thus freed from 

 both carbon dioxide and water vapor, is conducted through the tube 

 TF to a 3-way valve (F, figure 2) leading to the lungs of the subject. 



Unless the volume of respiration is wholly abnormal, the rate of 

 ventilation produced by the blower is sufficient to deliver enough 

 purified air at the junction of the 3-way valve and the main air pipe to 

 supply all that is needed, i. e., approximately 30 liters per minute. 

 If there is unusually rapid and deep inspiration, so that air is, for a 

 moment, drawn back from the spirometer, the extra wide tube, G, pro- 

 vides a minimum resistance between mouthpiece and spirometer. 



TEST FOR RATE OF VENTILATION. 



The spirometer, when filled, holds about 7 liters. The rate of venti- 

 lation may be approximately determined by opening the system at the 

 coupling, S (fig. 3), and pinching the tube, W, thus closing the intake 

 tube. Air from the spirometer is then discharged by the blower at 

 the open coupling, and the time in seconds is noted for the spirometer 

 to fall completely (350 mm.). If 15 seconds is required for the spirom- 

 eter to fall, the ventilation rate is approximately 28 liters per minute. 



ABSORBING SYSTEM. 



The calcium-chloride and soda-lime bottles are of simple form and, 

 for convenience, are placed upon a shelf attached to the base of the 

 apparatus. The soda lime is made by the formula of Haldane.^ It 

 has a distinct yellowish tint which changes to a chalky whiteness as the 

 carbon dioxide is absorbed by the reagent. The efficiency of the 

 reagent and the time for renewal may be judged by the progress of this 

 change in color. When a determination of the oxygen consumption 

 only is desired, as is usually the case, the calcium-chloride bottles may 

 be dispensed with. A greater efficiency of soda lime is thus obtained, 

 for it has been found that the moister the soda lime is, the greater is the 

 absorption of carbon dioxide. Indeed, the expired air may be passed 

 directly through the soda lime if care is taken that the excessive absorp- 

 tion of water does not make the absorbent so pasty as to interfere with 

 the free passage of air. As this is a very important point, the ventila- 

 tion rate should be frequently tested. 



If the reagent becomes exhausted the physiological effect is a some- 

 what labored respiration due to the unabsorbed carbon dioxide acting 

 as a stimulus to the respiratory center. This is not a serious defect and 



' Haldane, Journ. Physiol., 1892, 13, p. 422. The prepared soda lime may be purchased from 

 Stanley Jordan & Co., 93 Water Street, New York City. 



