METHOD FOB DETERMINING RESPIRATORY EXCHANGE IN MAN 



593 



to the water displaced by the bell to flow from the spirometer cylinder into a counter- 

 poise cylinder as the bell ascended out of the water. The bell, being heavier out of 

 water than when it is immersed, is accordingly counterpoised in any position, although 

 Carpenter has shown that this refinement is unnecessary. An opening in the top of 

 the spirometer permits the insertion of a rubber stopper, through which are passed a 

 thermometer, a water manometer, and a stopcock with tube for drawing the sample 

 of air. A scale on the side of the instrument gives the volume of the air. 



During an observation the subject sits in a reclining position or lies upon a couch. 

 When the bell of the spirometer is placed at zero, the mouthpiece adjusted in the 



A. B. 



Fig. 181. Haldane gas apparatus (A) and Pearce sampling tube (B). 



mouth, and the nose clamped, respiration is started, the expirations being passed 

 through the stopcock, which is so turned as to allow them to pass to the outside air. 

 After a few minutes the stopcock is turned so that the expirations are passed into 

 the spirometer for a definite length of time. At the end of the period the cock is 

 again turned, and after the barometric pressure, temperature, and volume of air have 

 been noted, the composition of the air is determined in the Haldane gas analysis ap- 

 paratus. 



4. THE DOUGLAS BAG. The Douglas bag is made of rubber-lined cloth, and is 

 capable of holding from 50 to 100 liters. It is especially useful for investigations 

 during exercise, since it is fitted with straps so that the bag can be fastened to the 



