METHOD FOR DETERMINING RESPIRATORY EXCHANGE IN MAN 561 



equal weight of water. The mark (13) on the stem of the bulb indi- 

 cates the level at which the solutions should stand. Enough pyrogallate 

 solution is introduced through tube 15 to fill bulbs 12 and 14 two-thirds 

 full. Then pyrogallate solution is poured into tube 16 until the differ- 

 ence in level of the fluids is sufficient to produce enough pressure to 

 raise the level of the pyrogallate solution in 12 to the level 13 on the 

 stem. Stopcock 8 must be open during this procedure. It may be neces- 

 sary to add or take away a little pyrogallate solution through 15 to at- 

 tain the above level. 



Care must be taken to allow for complete absorption of oxygen from 

 the air that is entrapped between 14 and 16 before an analysis is made ; 

 otherwise changes will be produced in the level of the pyrogallate solu- 

 tion. The air in the capillary tubing connecting the burettes with the 

 absorption bulbs must also be freed of C0 2 and 2 . This can be accom- 

 plished by making a dummy analysis of atmospheric air before the real 

 analysis. Great care must be taken to have atmospheric pressure in all 

 the tubes at the start of the analysis. This is accomplished by opening 

 the stopcock in the burette first to atmospheric air and then to the ab- 

 sorption bulbs, until no further change in the level of the fluids in the 

 stems of the absorption bulbs occurs. This level is then marked and 

 used as the standard. A small amount of water in the burette over the 

 mercury assures saturation of the air with water vapor. Time for drain- 

 age must be allowed before making readings. 



A very serviceable sampling tube for the transfer of air can be made 

 from a 30 c.c. ground-glass syringe, to which is attached a two-way 

 stopcock. 'A cut of this is shown in Fig. 181. The dead space in these 

 syringes is washed out by working the piston back and forth several 

 times. A thin coating of vaseline prevents leakage of the gas. We have 

 found that these sampling tubes will retain a sample of expired air with- 

 out change up to eight hours. 



MANIPULATION OF APPARATUS. The sampling syringe (20) is attached 

 to opening .2 of the burette, and its stopcock (17) opened to atmospheric air. 

 The level of the mercury is raised to the level of the stopcock of the syringe 

 and is then turned so that syringe and burette are in communication. The 

 bulb of mercury is lowered so that the mercury falls in the burette. This 

 draws the piston of the syringe with it, and fills the burette with air 

 from the syringe. It is advisable to put a little positive pressure on the 

 piston of the syringe in the maneuver to prevent possible leakage. When 

 all of the air is in the burette a slight positive pressure is produced in 

 the burette by gently pressing on the piston, and immediately there- 

 after the stopcock on the syringe (17) is again turned to the original 

 position. This allows the pressure of air in the burette to come to that 



